A Disk Galaxy of Old Stars at z ~ 2.5
60second-science(60秒科学)2014.6月 听力原文
Cool Kids Get Schooled With Age Kids deemed cool in early adolescence have a poor chance to keep that status by their early twenties, because their behavior gets old. Erika Beras reports.Here‟s something you might have figured out at your high school r eunion or by Facebook-stalking your old classmates: being one of the cool kids does not necessarily mean being cool for life. And now, a study in the journal Child Development confirms that suspicion. [Joseph P. Allen et al, What Ever Happened To The …Cool‟ Kids? Long-Term Sequelae Of Early Adolescent Pseudomature Behavior]Researchers followed ethnically and racially diverse suburban and urban kids from early adolescence to early adulthood. The kids who were deemed cool at a young age were high-status individuals with romantic relationships who broke rules and laws.But they were no longer viewed that way by peers by the time they were in their early 20‟s. The pseudo-mature behavior that seemed so admirable at a young age lost cache as the other kids gained actual maturity.Meanwhile, as the young James Deans and Miley Cyruses aged they had to engage in ever-riskier behavior to keep thinking of themselves as cool.By their early twenties, they were more likely to have drug and alcohol problems, relationship issues and criminal involvement. Turns out being a cool kid has a really short shelf life.—Erika Beras(The above text is a transcript of this podcast)White Bread May Actually Build Strong Bodies 1 WayThe guts of white bread eaters appear to contain more lactobacillus, a type of bacteria that wards off digestive disorders. Karen Hopkin reportsJun 20, 2014 |By Karen Hopkin[Audio of vintage Wonder Bread commercial]You can beat on Wonder Bread all you want. [Audio of columnist James Norton: “You can make a completely credible pillow out of this stuff.”]But it just keeps bouncing back—because despite its nutritional bad reputation, white bread appears to boost the growth of good gut bacteria. That‟s according to a pap er in the Journal of Agricultural and Food Chemistry. [Adriana Cuervo et al, Pilot Study of Diet and Microbiota: Interactive Associations of Fibers and Polyphenols with Human Intestinal Bacteria]In recent years, white bread has been shunned as a glutenous slab that lacks the health benefits of whole wheat. But this new study suggests there‟s more to the story.The researchers were looking at the effects of foods on the types of microbes that live in our intestines. They gathered data on the diets of 38 healthy adults and then analyzed the bacteria present in the subjects‟ stool samples. Hey, it‟s for science.Turns out that volunteers who ate white bread had more lactobacillus, a type of bacteria that wards off digestive disorders. Seems the starch and fibers in this sandwich staple are good for these germs.But before you make your lunch, another recent study showed that eating white bread is associated with obesity. So you should take all these findings with a pinch of salt. But not too much salt—especially if you have high blood pressure.—Karen Hopkin [The above text is a transcript of this podcast.]Plant Spores Hitch Long-Distance Feather RidesTiny spores from mosses, algae and lichens can stick in bird feathers, travel from the Arctic to the bottom of South America and grow into whole new specimens. Erika Beras reportsJun 18, 2014 |By Erika BerasYou could be in the Arctic and spot some moss. And then you could be at the tip of South America and spot the same kind of moss—and never find it in between. So how did this particular plant get so well-traveled? Turns out it flew.We‟ve long known that birds spread seeds. But new research says migrating birds also spread microscopic spores.The birds harbor tiny parts of plants and lichens in their feathers, setting up similar colonies thousands of miles apart. That‟s according to a study in the journal PeerJ. [Lily R. Lewis et al, First evidence of bryophyte diaspores in the plumage of transequatorial migrant birds]Scientists inspected feathers from birds in the Arctic that were about to leave for South America. Fragments from mosses, algae, lichens and liverworts were trapped in the feathers. All of which can grow into new whole organisms.The researchers think that long-distance fliers such as the American golden-plover and the white-rumped sandpiper picked up the spores while lining their nests. Then when the birds arrive in new places they molt, leaving behind the feathers and their precious cargo—to start growing again at the other end of the world.—Erika Beras [The above text is a transcript of this podcast.]Jellyfish Galaxies Get Guts Ripped OutRecently discovered galaxies shaped like jellyfish leave a long trail of hot gas and dust, victims of even hotter gas from their surrounding cluster of galaxiesJun 17, 2014 |By Ken Croswell and Steve MirskyA recently discovered breed of galaxies really caught astronomers‟ attention. Because they look like jellyfish.Astronomers found the first jellyfish galaxy a decade ago. Such a galaxy has a disk of stars, like our Milky Way—plus long blue tendrils. A jellyfish galaxy was once a spiral like the Milky Way, spawning new stars from its gas and dust. But unlike the Milky Way, a jellyfish belongs to a cluster of galaxies.A recent analysis of Hubble telescope images led to the conclusion that extremely hot gas from the cluster is behind the formation of jellyfish. That study is in the Astrophysical Journal Letters. [H. Ebeling, L. N. Stephenson, and A. C. Edge, Jellyfish: Evidence of extreme ram-pressure stripping in massive galaxy clusters]As the galaxy plows through space, this hot gas rips out the galaxy's own gas and dust, forming the long streamers behind the galaxy. This torn-out gas still gives birth to new stars. The brightest of these newborn stars shine blue. So the former disc-shaped galaxy metamorphosizes into a celestial jellyfish sporting long blue tendrils.The galaxy will eventually literally run out of gas, and thus lose the ability to create any more new stars. Jellyfish in the sea can be deadly. But in space, the mortally wounded victim is the jellyfish galaxy itself.—written by Ken Croswell, voiced by Steve Mirsky [The above text is a transcript of this podcast.]2-Face Moon Tells How It Got That WayA new analysis says that the asymmetry between the two faces of the moon is due to crust thickness differences that resulted from variable cooling rates after the molten formation of our companion. Karen Hopkin reportsJun 13, 2014 |By Karen HopkinThe dark side of the moon. It‟s remote and mysterious. And not just because we can‟t see it from Earth. When viewed from space, th e moon‟s back side looks totally different from its front. Now, researchers think they have a solution to the mystery, which they share in the Astrophysical Journal Letters. [Arpita Roy, Jason T. Wright, and Steinn Sigurðsson, Earthshine on a Young Moon: Explaining the Lunar Farside Highlands]You may have wondered about the "man in the moon," that facelike image made by the large flat plains on the lunar surface that faces us. But scientists wonder why the far side doesn‟t have comparable features.According to the new analysis, this asymmetry has to do with how the moon was made. Not long after the Earth formed, a Mars-sized hunk of intergalactic debris smacked into our baby planet, flinging off material that then became the moon. The crash left both bodies boiling hot. But the smaller moon cooled down more quickly than the molten Earth… especially the part that faced the other way.The minerals on the moon‟s cooler side started to p recipitate sooner. That head start gave the far side a thicker crust, which is more resistant to the weathering seen on the familiar side: weathering that gives a face character. Even on the moon.—Karen Hopkin [The above text is a transcript of this podcast.]Classroom Decorations Can Distract Young StudentsFive-year-olds in highly decorated classrooms were less able to hold their focus, spent more time off-task and had smaller learning gains than kids in bare rooms. Erika Beras reportsJun 11, 2014 |By Erika BerasRemember your kindergarten classroom? The maps on the wall, the charts of the seasons on bulletin boards, the alphabet over the blackboard? I know I spent hours staring at the brightly colored decorations—and not listening to what my teacher was saying. Maybe you did, too. And it looks like we‟re not alone.The more decorations in a classroom, the more distracted students may be. So finds a study in the journal Psychological Science. [Anna K. Fisher, Karrie E. Godwin and Howard Seltman, Visual Environment, Attention Allocation, and Learning in Young Children: When Too Much of a Good Thing May Be Bad]Researchers observed five-year-olds in highly decorated classrooms and in classrooms that were relatively bare. And the kids were less able to hold their focus, spent more time off-task and had smaller learning gains in the busy rooms than in the bare rooms.At that young age, attention regulation skills aren‟t fully formed. And yet it‟s at that stage of development that children find themselves surrounded by decorations irrelevant to what t hey‟re learning at any given time.The researchers are not prescribing a change from busy to bare rooms. They say there is more research to be done. But this study, along with previous work, suggests that the visual environment can affect how young childr en learn their reading, writing and …rithmetic.—Erika Beras[The above text is a transcript of this podcast.]Kid Scientist Finds Sweet Pest ControlEleven-year-old Simon Kaschock-Marenda's science fair project led to a publication about the insecticidal effects of the sweetener Truvia. Karen Hopkin reportsJun 10, 2014 |By Karen HopkinYou can catch more flies with honey than with vinegar. But if you want to kill them, you might try Truvia. Because a new study shows that the active ingredient in this popular sweetener can act as an insecticide.The study began as a sixth-grade science-fair project. Eleven-year-old Simon Kaschock-Marenda noticed that his parents had stopped using sugar. So he decided to see how different sweeteners affect the health of fruit flies. He and his dad, a card-carrying biologist, offered the flies food spiked with a variety of no-cal sweeteners. Six days into the experiment all the Truvia-fed flies were dead, while those stuck with Sweet-n-low, Splenda or Equal lived five to seven weeks.Why Truvia makes flies drop like flies is still a mystery. Back in the lab, the researchers confirmed that the bugs weren‟t starving: they all continued to eat. Mos t actually seemed to prefer Truvia to real sugar when offered a choice, findings published in the journal PLoS One. [Kaitlin M. Baudier et al, Erythritol, a Non-Nutritive Sugar Alcohol Sweetener and the Main Component of Truvia®, Is a Palatable Ingested Insecticide]Next, the researchers will see if the sweetener kills other bugs, like cockroaches or ants. Until then, try tossing a little Truvia in your coffee, and on the counter.—Karen Hopkin [The above text is a transcript of this podcast.]Light Colors Become Fashion Rage for Northern Europe's InsectsAs northern Europe warms, the light-colored butterflies and dragonflies typically found in the Mediterranean are moving north, and outcompeting their darker-colored rivals. Erika Beras reportsJun 9, 2014 |By Erika BerasFor insects in Europe, climate change has led to habitat change. In the past couple of decades, for example, Mediterranean butterfly and dragonfly species have been found flying around places previously off limits to them—new new northern climes such as Germany.Now a study in Nature Communications finds a colorful reason for the northern expansion. As northern Europe warms, the light-colored butterflies and dragonflies typically found in the Mediterranean find themselves able to survive in the newly warmer north, and to even outcompete their darker-colored rivals. [Dirk Zeuss et al, Global warming favours light-coloured insects in Europe]Lighter colors reflect sunlight while dark colors absorb it and heat up. Hence chocolate ice cream melts in the sun faster than vanilla. Lighter-colored insects thus function well in warmer climates. They don‟t overheat as easily and can stay active longer, giving them a leg up—well, six legs up—in our warming world.The researchers say this migrat ion of insects shows that climate change isn‟t something that‟s coming—it‟s already happening. And it could drastically affect which insects up end up where. Which will in turn affect us.—Erika Beras[The above text is a transcript of this podcast.][Scientific American is part of Nature Publishing Group.]London Fish Chip Away atHistorical UnknownsIsotope composition within fish tails found in London archaeological digs shows that the city began importing cod from northern Scandinavia some 800 years ago. Cynthia Graber reportsJun 6, 2014 |By Cynthia GraberLondoners love their fish. And according to a new study, in the early 13th Century they suddenly started importing it from as far away as the Arctic near Norway. The research is in the journal Antiquity. [David C. Orton et al, Fish for the city: meta-analysis of archaeological cod remains and the growth of London's northern trade]About the year 1000, sea fishing increased significantly in northern Europe. To see how that increase influenced urban growth, researchers looked at 95 excavation sites in London. Which included about 3,000 bones from cod fish.Cod are decapitated before being dried for transport. So finding heads meant the fish were local. And the researchers found that as fish heads appear to decrease in the early 1200s, fish tails dramatically increased—a sign of importation.Examination of the chemical isotopes in the tails matched those for fish in waters far to the north, probably off Norway close to the Arctic, more evidence of import.The scientists do not know if the rapid switch from local to imported cod happened because local fish were n‟t as plentiful as the population increased, or if the market became flooded with dried imports from the north. But these fish tails tell a story of London becoming a growing economic center, and part of a globalizing fish trade.—Cynthia Graber [The above text is a transcript of this podcast.]Meteor Storm Went from Sizzle to FizzleThe May Camelopardalids meteor outburst turned out to be a dud, because meteor storm prediction is not a sure thing, unlike, for example, calculating the next eclipseJun 4, 2014 |By Ken Croswell and Steve MirskyWhat if they held a meteor storm and no meteors came? That's what many people are asking after the well-hyped May Camelopardalids meteor outburst turned out to be a dud.Most meteors arise from mere dust grains and pebbles in space. When Earth passes through a stream of this debris shed by a comet, the particles burn up in our atmosphere, and we see a meteor shower.Some astronomers had predicted that on the night of May 23, particles from a comet called LINEAR would bring many meteors to the night sky. North America had the best seats for the event.And so a lot of people watched and waited. But no one saw much.Meteor showers are common, and the best produce about a hundred meteors per hour. But meteor storms, which can send out thousands of meteors per hour, are rare and notoriously unreliable.Not only can predicted storms go bust, but great storms can erupt without warning. In November 1966, the normally weak Leonids surprised everyone and roared back to life, producing more than 100,000 shooting stars in a single hour.You can still count on astronomers to tell you exactly when the next eclipse will be. But if they ever promise you a meteor storm, you should take it with a grain of, well, meteor dust.—written by Ken Croswell, voiced by Steve Mirsky [The above text is a transcript of this podcast.]。
黑洞的由来的英语作文
黑洞的由来的英语作文The Origin of Black Holes: A Journey into Cosmic Mysteries。
Introduction。
Black holes, enigmatic entities lurking in the depthsof space, have captivated the imagination of scientists and laypersons alike. Their origins, shrouded in cosmic mystery, have been the subject of intense study and speculation. In this essay, we embark on a journey to unravel the secretsof black holes, exploring their formation, properties, and significance in the universe.Formation of Black Holes。
The genesis of black holes begins with the demise of massive stars. When a massive star exhausts its nuclear fuel, it undergoes a cataclysmic event known as a supernova explosion. During this explosive phase, the outer layers ofthe star are ejected into space, while its core undergoes gravitational collapse. If the core's mass exceeds acritical threshold, it collapses into a singularity—a point of infinite density—giving birth to a black hole.The process of black hole formation can also occur through the gravitational collapse of dense stellar remnants, such as neutron stars, or through the merger of two compact objects, such as neutron stars or black holes. These pathways lead to the creation of different types of black holes, ranging from stellar-mass black holes to supermassive black holes found at the centers of galaxies.Properties of Black Holes。
红移z≈2极亮红外星系的研究进展
红移z≈2极亮红外星系的研究进展方官文;林泽森;孔旭【摘要】极亮红外星系(ULIRGs)是指红外(IR,8～1 000 μm)光度LIR＞1012 L☉的一类星系.研究表明,红移z≈2处极亮红外星系是大质量(M*＞1011 M☉)、富尘埃和强恒星形成(大于100 M☉·a-1)的特殊星系.极亮红外星系可分成活动星系核起主导作用的源和恒星形成占主导的星系.恒星形成主导的源,中红外光谱有明显的多环芳香烃辐射;而活动星系核主导的星系,光谱呈现出幂律形式并有很强的硅线吸收.极亮红外星系的静止光学波段形态存在多样化,既有并合结构特征,又有椭圆形态.这类星系很可能是近邻大质量宁静星系的前身星系.介绍了红移z=2附近极亮红外星系的各种物理性质的研究进展,如形态和结构、光谱特征、成团性、尘埃分布和形成机制等,以及阐述了该领域未来的研究方向.%UltraLuminous InfraRed Galaxies (ULIRGs) are galaxies defined to have extremely high infrared (IR) luminosities (LIR ＞1012 L☉).Observations have shown that high-redshift ULIRGs are massive galaxies (M* ＞1011 M☉),with extremely high ratio of infrared to optical flux density (F24 μm/FR ＞ 1 000) and intensive star formation (100 ～1 000 M☉ · a-1).These objects are relatively rare at z ≈ 0,but their space density rapidly increase with look-back time and apparently peaks around z =2 ～ 3.Upon it's discovery,ULIRGs were suggested to be a feasible evolutionary phase towards the formation of local massive early-type galaxies.Their rest-frame optical morphologies show that high-redshift ULIRGs are a mixture of mergers or interacting systems,irregular galaxies,disks,and ellipticals.The morphological diversities of ULIRGs suggest that there are different formation processes for thesegalaxies.Merger processes between galaxies and disk instabilities play an important role in the formation and evolution of ULIRGs at high redshift.Mid-infrared (MIR) spectra of ULIRGs are observed with the Spitzer/IRS (InfraRed Spectrograph) instrument.For ULIRGs at z ≈ 2,major spectral features including the PAH (Polycyclic Aromatic Hydrocarbon) emission features at 7.7,8.6,and 11.3 μm and silicate absorption from 8 to 13 μm (peaking at 9.7 μm) fall in the observable wavelength range.ULIRGs can be divided into two types according to their MIR spectra.Objects with strong power-law continua are powered mainly by active galactic nuclei (AGNs),while those with a strong PAH emission are powered by intensive star formation.The clustering signal of ULIRGs roughly corresponds to a correlation length of r0 =7.40 h-1.Mpc for the full F24 μm ＞ 0.3 mJy sample.The clustering strength increases with luminosity,up to r0 =12.97 h-1.Mpc for F24 μm ＞ 0.6 mJy ULIRGs.Moreover,observations demonstrate that a median dust temperature is about 40 K for ULIRGs at z ≈ 2.【期刊名称】《天文学进展》【年(卷),期】2017(035)001【总页数】19页(P16-34)【关键词】高红移星系;星系观测;星系形态;星系光谱;星系成团性【作者】方官文;林泽森;孔旭【作者单位】大理大学天文与科技史研究所,大理671003;中国科学技术大学天文学系,合肥230026;中国科学院星系与宇宙学重点实验室,合肥230026;中国科学技术大学天文学系,合肥230026;中国科学院星系与宇宙学重点实验室,合肥230026【正文语种】中文【中图分类】P157.1相对于近邻星系，高红移 (特别是红移 z=2 附近)大质量星系的形成和演化研究也有着非常重要的意义。
银河系的结构和演化
1920年H. Shapley（美）发现球状星团均匀 地分布在银河的两侧，并且有向人马座聚集的 倾向。 Shapley利用球状星团内的天琴RR型变星测 量星团距离，并给出球状星团的空间分布。
The Creater Milky Way
Shapley认为球状星团是银 河系的子系统，并以银心为 分布中心。 Shapley估计太阳系到银心 的距离为16 kpc. 在Shapley的模型中，银河 系的结构是扁盘状的，直径 为100 kpc. 1kpc=3.262光年
厚盘的形成和演化成为天体物理研 究的新热点
随着银河系厚盘的发现，原来关于银河系恒星分 布的3成分(核球+银盘+银晕)模型，应代之以4 成分(核球+薄盘+厚盘+银晕)模型。 今天，银河系厚盘的存在，已经为天文界所普遍 接受。不仅如此，在一些河外旋涡星系中也发现 了存在厚盘的观测证据。 因此，至少对一部分星系来说，厚盘很可能是星 系结构中普遍存在的一种成分，它的形成和性质 必然与星系演化过程密切相关。
利用实测资料确定函数的具体形式(D0和h的值)，便成为 研究银河系结构和恒星分布的主要内容之一。 自赫歇尔时代以来，天文学家一直认为银盘中恒星只具 有单一的指数分布结构——银盘，仅此而已。
厚盘的发现
1 9 8 3 年， 两位英国天文学家吉尔莫(N.Gilmore) 和莱德(G.Reid)经过详细的研究后首次明确提出， 银盘中的恒星可以分属于薄盘和厚盘两种形态不 同的结构。 他们发现，恒星在垂直银道面方向上的分布需要 用2个指数成分来表述：在银面距z≤1000pc内，银 盘恒星可以用一个指数分布来描述，标高约为 300pc, 这就是薄盘，也就是原来意义上的银盘。 另一方面，在银面距z=1000〜5000pc范围内的恒 星主要属于第二个指数成分，标高约为1450pc, 称 为厚盘。
高一年级英语天文知识单选题40题
高一年级英语天文知识单选题40题1. Which planet is known as the "Red Planet" because of its reddish appearance?A. EarthB. MarsC. JupiterD. Venus答案：B。
解析：在太阳系中，火星（Mars）因为其表面呈现出红色的外观而被称为“Red Planet（ 红色星球）”。
地球（Earth）是我们居住的蓝色星球；木星（Jupiter）是一个巨大的气态行星，外观不是红色；金星 Venus）表面被浓厚的大气层覆盖，不是以红色外观著称。
2. Which planet has the most moons in the solar system?A. EarthB. MarsC. JupiterD. Mercury答案：C。
解析：木星（Jupiter）是太阳系中拥有最多卫星（moons）的行星。
地球（Earth）只有一颗卫星；火星（Mars）有两颗卫星；水星 Mercury）没有卫星。
3. The planet with the shortest orbit around the Sun is _.A. MercuryB. VenusC. EarthD. Mars答案：A。
解析：水星（Mercury）是距离太阳最近的行星，它的公转轨道是最短的。
金星 Venus）、地球 Earth）、火星 Mars）距离太阳比水星远，它们的公转轨道都比水星长。
4. Which planet has a thick atmosphere mainly composed of carbon dioxide?A. EarthB. MarsC. VenusD. Jupiter答案：C。
解析：金星（Venus）有一层非常厚的大气层，其主要成分是二氧化碳 carbon dioxide）。
地球 Earth）的大气层主要由氮气和氧气等组成；火星（Mars）大气层很稀薄，主要成分虽然有二氧化碳但比例和金星不同；木星（Jupiter）的大气层主要由氢和氦等组成。
大学里令人印象深刻的事情英语作文
大学里令人印象深刻的事情英语作文全文共3篇示例，供读者参考篇1The Most Amazing Day at My Big Sister's CollegeMy big sister Emily is in her third year of college, and I went to visit her campus last weekend. It was the coolest experience ever! I'm only 10 years old, but I learned so many incredible things that I can't wait to go to college myself someday.Emily goes to a huge university with over 30,000 students! Can you imagine having class with that many kids? Their campus is like its own little city, with dorms, cafeterias, libraries, labs, gyms, and everything you could ever need. It's way bigger than my elementary school.On Saturday morning, Emily took me on a tour around the main parts of campus. We saw the iconic old stone buildings where a lot of the classes happen. Emily says some of them are over 100 years old! They have these giant lecture halls that can fit hundreds of students at once. The biggest one we peeked into had stadium-style seating and could probably hold my entire elementary school. So wild!After the classroom buildings, we walked through the residential areas where all the dorms are. Emily lives in a big dorm called Briggs Hall with her friends Sarah and Jess. Their room is kind of small but they decorate it with tapestries, string lights, and photos to make it cozy. We got to meet Sarah and Jess and they were really nice to me.Then Emily showed me the best part of campus - the Student Union! This awesome four-story building has a food court, lounge areas, a game room, workout facilities, and more. We had chicken tenders and fries at the food court and they were delicious. In the game room, there were pool tables, video games, and even VR headsets to try. A bunch of students were hanging out playing games and watching TV together. It looked like such a fun place to hang out with friends between classes.But the absolute coolest thing we did was attend Emily's biology lab in the afternoon. I had never been inside a real science lab before! Everyone had to wear special goggles and coats to stay safe. There were all these crazy machines, beakers, test tubes, and tiny tools I had never seen.Emily's lab professor is studying genetics and DNA. For their experiment that day, they were extracting DNA from strawberries! The professor showed us how to blend up thestrawberries, mix in some chemicals, and then slowly pull out the strands of strawberry DNA. It looked like a tangle of slimy white strings. So gross but fascinating! I got to do it myself and now have a little tube of strawberry DNA to keep. Who knew you could extract the building blocks of life from fruit?After the lab, Emily's friend Raj gave us a tour of the engineering lab where he works on robotics projects. They are trying to build robots that can rescue people after natural disasters happen. Raj showed me how they use coding to program the robots' movements and decision making. I even got to control one of the simple robots and make it move around! I had so much fun.The engineering students then showed me their 3D printers which can print out 3D objects from a computer design. They let me design a little 3D figure of myself online and then printed it out right in front of me. I got to take the 3D printed me home as a souvenir!By the time we left campus, my head was spinning from all the incredible things I had seen and done that day. College is a place where students get to explore so many fascinating subjects, try out future careers, and immerse themselves in anenvironment of learning and discovery. They have freedoms and resources that kids in elementary school can only dream about.I already can't wait to go to college and have experiences like Emily. Maybe I'll study robotics like her friend Raj, or genetics like her biology professor. Or maybe I'll find a calling in something I haven't even heard of yet! The possibilities seem endless.College looks like a place where you can follow your biggest passions and turn them into a career that helps make the world better. You get to learn directly from experts, not just read about things in textbooks. And you're constantly surrounded by people who love learning as much as you do.While elementary school is fun, it will be amazing to one day have that level of independence. To live on your own, create your own schedule, and decide how to spend your days. No more raising your hand to go to the bathroom or asking for a hall pass. Just freedom to explore and grow.I hope that when I'm Emily's age, colleges still have amazing facilities like the ones I saw. With technology always evolving, who knows what else they'll have? Maybe they'll be teaching us how to build spaceships or edit DNA to cure diseases. Or download information directly into our brains like in the movieThe Matrix! As mindblowing as Emily's college already is, I can only imagine howmuch more advanced it will all be in 10 more years.If this visit showed me anything, it's that the world is full of endless learning opportunities, especially at the college level. There is so much left to discover and understand, not just about science and technology, but about the world around us.While I'm proud of the things I've learned in elementary school so far, I can't wait to one day trade in my times tables and reading groups for physics and philosophy lectures. To go from arts and crafts to genetic experiments. From simple coding games to programming rescue robots. That's the kind of education that can open up an entire universe of knowledge and potential.College is the first step towards an amazing career and becoming an adult who never stops exploring. People often say that college will be the best four years of your life. But after seeing Emily's campus, classes, and lab work, I think those four years are just the beginning of an incredible life full of discovery and growth. Elementary school better get ready, because in a few years, this curious kid is coming for that college experience!篇2The Most Amazing Thing in CollegeHi there! My name is Tommy and I'm going to tell you about the most awesome thing that happened to me in college. Are you ready? Okay, here we go!It was my first year and I was really nervous because everything was so new and different from elementary school. The buildings were huge, the classes had hundreds of students, and I felt so small. But I was also excited to learn all sorts of new things and make friends from all over.In my first semester, I had this really cool class called "Introduction to Astronomy." Can you guess what it was about? That's right - stars, planets, galaxies, and the whole universe! I've always loved looking up at the night sky and wondering what's out there.Our professor was this older guy with crazy white hair who looked like Albert Einstein. His name was Dr. Hubble, just like the famous telescope! On the first day, he said, "Astronomy will change how you see the world and your place in it." I wasn't sure what he meant, but I couldn't wait to find out.In the first few weeks, we learned about the solar system, how the planets orbit the sun, and why we have seasons on Earth. It was all really interesting, but nothing too mind-blowing yet. Then one day, Dr. Hubble rolled in this huge fancy telescope and said we were going to learn how to use it!That night, we all went up to the observatory on the roof of the science building. It was a circular room with a massive telescope pointing up at the sky through an open dome. The telescope was as tall as a giraffe and had all these knobs, dials, and computers attached to it. I felt like I was in a spaceship!Dr. Hubble showed us how to calibrate the telescope to focus on different objects in the sky. First, we looked at the moon. Can you believe that the moon is around 238,000 miles away? But through that powerful telescope, it looked so close and clear that I could see all the craters and mountains. It was awesome!But as cool as the moon was, nothing could have prepared me for what came next. Dr. Hubble aimed the telescope at a tiny smudge in the sky that didn't look like much to my naked eye. But when I looked through that viewfinder...my jaw just dropped.What I saw was a spiral galaxy - a giant spinning disk of billions of stars, with bright arms curling around a glowing center! The spiral was so clear and colorful, almost like seeing a picturefrom the Hubble Space Telescope itself. Except this wasn't a picture - this was real. A galaxy hanging there in the vastness of space, light years away!Dr. Hubble explained that this galaxy is called the Whirlpool Galaxy, and its light has traveled over 30 million years to reach us.30 million years! I was seeing light that left that galaxy when dinosaurs still roamed the Earth. My mind was completely blown.Over the next few weeks, we looked at more galaxies, nebulae full of glowing clouds of gas and dust, and even a couple of distant quasars from the early universe. Each sight was more mind-bending than the last.But you know what the wildest thing was? Dr. Hubble told us that there are over 100 billion galaxies in the observable universe, each one a massive Island Universe with billions or even trillions of stars. Our own galaxy, the Milky Way, has over 200 billion stars in it! And our solar system, our sun and planets, are just one tiny speck orbiting one of those stars.It's just...incredible to think about how vast and ancient the universe is. That we are living on a planet circling one star out of 200 billion in our galaxy, which is just one of 100 billion galaxies. Space is so huge and filled with so much...stuff! Stars being born, galaxies colliding, black holes devouring everything aroundthem. The more I learned in that astronomy class, the smaller I felt.But in a good way, you know? Like, realizing that I'm a little speck in this incomprehensibly enormous cosmos made me feel amazed, not insignificant. There are all these incredible things happening every second across the universe, on scales of size and time that I can barely even imagine. And with that awesome telescope, I got to see just a tiny fraction of it with my own eyes.That astronomy class gave me a deeper perspective on my place in the universe than I could have ever gotten from just reading about it. Actually seeing those distant galaxies and nebulae was one of the most humbling, awe-inspiring, incredible experiences of my life so far.And that's why it left such a big impression on me. Sure, doing well on a test or joining a club is cool and all. But getting that direct window into the vast, amazing, ancient universe we live in? Having my mind blown like that as I stared through the eyepiece at sights no human had ever seen before? That's the type of experience that shakes you to your core and gives you a new appreciation for how astounding the cosmos truly is.I don't know about you, but experiences like that are why I love learning and can't wait to see what other amazing things arein store for me at college. If an introductory astronomy class could be so incredible, I can only imagine what othermind-bending revelations await! The universe is full of untold wonders, and I'm going to spend my college years trying to understand as many of them as I possibly can.Anyway, that's my story of the most amazing, impressive thing that's happened to me so far at university. I hope it inspires you to look up at the night sky with a new sense of wonder and curiosity. Who knows - maybe you'll grow up to be an astronaut or make the next big discovery about our universe! The cosmos is a vast, fantastic, mind-boggling place full of mysteries just waiting to be unraveled. What an exciting thought!Thanks for reading, and safe travels amongst the stars! Talk to you next time!篇3The Most Amazing Thing I Saw at UniversityWow, you'll never believe what happened to me last week! I got to go visit my big sister Sarah at her university and it was the coolest experience ever. I'm only 10 years old, but I already can't wait to go to university myself one day.Sarah is studying science at a really big school a few hours away from our house. She's super smart and always getting good grades. I was so excited when Mom and Dad said I could skip school for a day and go see where Sarah learns and lives. We took the train to get there, which was already a fun adventure for me.When we arrived on campus, I was amazed by how huge it was! There were buildings everywhere, some old and fancy looking, others modern and sleek. Zillions of students were walking around between classes, chatting with friends or studying outside on the lawns. The grassy areas had tons of trees and flowerbeds too, making it feel like a park sprawled across the whole place.After meeting up with Sarah, we walked over to the science part of campus. That's when I saw the most mind-blowing thing of all - the nuclear reactor building! I couldn't believe an actual university would have something like that. Sarah explained that it's a really small, safe reactor that students use to learn about nuclear physics and run experiments. Still, just knowing there was a real nuclear reactor on campus made me feel like I was in some kind of secret science lab!We didn't get to go inside the reactor area for safety reasons, but Sarah's professor gave us an awesome tour of the rest of the science facilities. I got to see lasers being used to study molecules, a room full of powerful microscopes, and a huge machine that simulates different planetary environments. We even visited a clean room where students make computer chips and build small satellites to launch into space!All the equipment and technology everywhere looked like something out of a sci-fi movie. I just couldn't wrap my10-year-old brain around how advanced it all was. Like some kind of crazy futuristic wonderland! It made me want to learn as much as possible so maybe I could operate all those incredible machines myself one day.After the tour, we attended one of Sarah's chemistry lectures in this giant auditorium classroom. I wasn't able to follow most of what the professor was saying since it was pretty advanced stuff. But I loved watching him do exciting experiments right there in front of us, like making brightly colored firework-looking reactions in glass beakers. He even had a small explosion at one point that made me jump in my seat!The professor was really funny too, joking around in between all the serious science. I could tell Sarah and herclassmates really enjoyed and respected him. It seemed like such an engaging way to learn compared to regular school lectures where we just sit quietly taking notes as the teacher drones on and on.After the thrilling chemistry show was over, we stopped for lunch at one of the dining halls. I've never seen a bigger restaurant in my life! It was like a cafeteria the size of a football stadium with dozens of different food stations selling everything from pizza to stir-fry. Students could drink as much soda and milk as they wanted, which seemed like the wildest dream for a kid like me who has to beg Mom for just one small juice box as a treat.While we were noshing on our mountain of french fries, a bunch of engineering students wheeled what looked like ago-kart type vehicle right through the dining area! Apparently it was just a regular old science project for one of their classes and they were transporting it across campus. At a university, no one even bats an eye at stuff like that. Sarah said we're also likely to see students carrying rocket parts or metal sculptures to their workspace on any given day. Just another Tuesday there!The last stop on our tour was Sarah's dorm where she lives with her friends. I was immediately jealous that she gets her ownbedroom instead of having to share one with our annoying little brother. The dorm was pretty basic, but still huge compared to our rooms at home. And they have a gym, rec room with TVs and video games, and even a dining hall just for kids living there. Definitely an upgrade from our house!As we were leaving, Sarah pointed out a group of students lying out in their bathing suits on the grass, getting some sun. I guess at university you can tan and relax between classes if you want! Some kids were also shooting hoops at the outdoor basketball courts and playing frisbee in the quads. I couldn't imagine having that kind of free time and independence during a regular school day.On the train ride home, Mom asked me what I thought the most impressive part of the university was. At first, I was going to say the nuclear reactor for sure. But then I realized the most amazing thing wasn't any specific lab or piece of equipment or facility. It was the entire environment and experience of being at a university.It's just such a vibrant, free place full of passionate people dedicated to learning and making new discoveries every day. Students and professors seem way more enthusiastic about their studies than kids are at regular schools too. I mean, where elsedo you see people building satellites and driving go-karts around as part of their homework?University seems like this wondrous mix of work and play, seriousness and creativity, all smushed together in the coolest way possible. You get to learn mind-expanding things using incredible technology and resources. But you also get the freedom to study whatever bizarre topics interest you most, ask endless questions, and just enjoy being young and making friends at the same time.I'm still just a little kid who can barely multiply fractions. But visiting Sarah's university gave me the most fantastic glimpse at the kind of amazing opportunities that lie ahead if I keep working hard. Instead of dreading more boring years at my regular elementary school, I can't wait to grow up and experience that entire vibrant world of higher learning myself one day. University is definitely going to be the best time of my life!。
河外星系的认识和分类
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Disk Component: stars of all ages, many gas clouds
Spheroidal Component: bulge & halo, old stars, few gas clouds
Blue-white color indicates ongoing star formation
Hubble Deep Field
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Hubble Ultra Deep Field
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Hubble Ultra Deep Field
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Hubble Ultra Deep Field
第六章 河外星系
研究历史
星系分类 星系测量 特殊星系 星系团 星系演化
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研究历史
公元前5世纪，希腊哲学家德谟克利特：银 河是由无数恒星所构成，太暗而不能区分
公元前3世纪，希腊哲学家亚里士多德 ： 银河是纯粹的大气现象，是地球发出的水 蒸汽
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第六章 河外星系
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研究历史 星系分类 星系测量 特殊星系 星系团 星系演化
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What are the three major types of galaxies?
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满天星的英语作文要从远到近的英语作文
满天星的英语作文要从远到近的英语作文全文共3篇示例，供读者参考篇1The Vast Expanse: My Journey Through the Milky WayAs I gaze up at the twinkling stars that adorn the night sky, I can't help but feel a sense of wonder and curiosity about the vastness of our universe. Tonight, I embark on a literary journey, exploring the Milky Way galaxy from the farthest reaches to our cosmic backyard, unraveling the mysteries that have captivated stargazers for centuries.Part I: The Edge of the Observable UniverseLet us begin our adventure at the very limits of what our telescopes can detect, where the faint whispers of ancient galaxies beckon us. Here, we encounter the cosmic microwave background radiation, a faint glow that permeates the cosmos –a relic of the Big Bang itself. This primordial sea of light serves as a snapshot of the universe's infancy, a mere 380,000 years after its birth.Billions of light-years away, quasi-stellar radio sources, or quasars, blaze with the intensity of a trillion suns. Theseenigmatic objects, powered by supermassive black holes at the cores of distant galaxies, offer tantalizing glimpses into the earliest epochs of the universe's history. Their brilliant beacons serve as cosmic lighthouses, guiding our exploration ever deeper into the cosmos.Part II: The Realm of GalaxiesAs we journey inward, we encounter a vast tapestry of galaxies – cosmic cities teeming with billions of stars, each with its own story to tell. From the majestic spiral arms of the Andromeda Galaxy, our nearest galactic neighbor, to the elegant elliptical galaxies that grace the celestial canvas, these celestial metropolises showcase the incredible diversity of structures that populate the universe.Deep within these galactic realms, we witness the births and deaths of stars, cosmic crucibles where the elements that make up our world are forged. Nebulae, glowing clouds of gas and dust, serve as stellar nurseries, nurturing the next generation of suns. Simultaneously, the explosive finales of dying stars seed the cosmos with the building blocks of life, enriching the interstellar medium with the heavy elements that will one day form planets and, perhaps, life itself.Part III: Our Galactic HomeCloser still, we find ourselves within the embrace of our own celestial abode, the Milky Way Galaxy. This majestic spiral, a vast cosmic pinwheel spanning over 100,000 light-years, is our cosmic address – a place we call home.At the heart of our galaxy lies a supermassive black hole, a gravitational behemoth that exerts its influence over the entire system. Around this cosmic anchor, hundreds of billions of stars dance in a graceful cosmic ballet, tracing intricate orbits through the galactic disk.Among these countless stellar companions, we find our own sun, a humble yet vital star that sustains life on Earth. From our vantage point within the Milky Way's spiral arms, we can marvel at the rich tapestry of star clusters, nebulae, and even other galaxies that grace our celestial neighborhood.Part IV: Our Cosmic BackyardFinally, we arrive at our cosmic backyard, the solar system – a tiny corner of the universe that we have come to know and love. Here, we witness the intricate dance of planets, moons, and countless other celestial bodies, each with its own unique character and mysteries to unravel.From the scorching furnace of Mercury to the icy realms of the dwarf planets that dwell in the Kuiper Belt, our solar system is a microcosm of the universe itself. We stand in awe of the breathtaking vistas of the gas giants, Jupiter and Saturn, with their intricate systems of moons and rings. And closer to home, we find our own blue marble, Earth – a living, breathing world teeming with life and wonder.As I conclude my journey through the Milky Way, from the farthest reaches of the observable universe to our own cosmic backyard, I am filled with a profound sense of awe and humility. The vastness of the cosmos reminds us of our insignificance, yet the intricate dance of celestial bodies reminds us of the beauty and complexity that permeates the universe.This exploration has only scratched the surface of the wonders that lie beyond our planet, and I am filled with a renewed sense of curiosity and a thirst for knowledge. The universe is a vast tapestry of mysteries waiting to be unraveled, and I am eager to embark on further journeys of discovery, uncovering the secrets that lie hidden among the stars.篇2The Wonders of the Stars: A Journey from the Cosmic to the TerrestrialAs I gaze up at the twinkling lights adorning the night sky, I am filled with a profound sense of wonder and humility. The stars, those celestial beacons that have captivated humanity since the dawn of time, hold within them a myriad of secrets waiting to be unraveled. Let us embark on a journey, one that spans the vast expanse of the cosmos, traversing the uncharted realms of the universe before returning to our terrestrial abode.Across the Cosmic ExpanseAt the heart of our exploration lies the enigmatic nature of galaxies, those colossal assemblages of stars, gas, and dust that populate the observable universe. The Milky Way, our celestial home, is but a single entity among billions of galaxies that stretch across the cosmic tapestry. Each galaxy harbors its own unique story, forged from the intricate interplay of gravitational forces, stellar evolution, and the relentless passage of time.As we peer deeper into the cosmic abyss, we encounter quasars – the brightest and most energetic celestial objects known to us. These enigmatic entities, powered by supermassive black holes at the cores of distant galaxies, shine with a brilliance that outshines entire galaxies. Their existence challenges ourunderstanding of the fundamental laws of physics and pushes the boundaries of our scientific knowledge.Closer to Home: Our Solar SystemVenturing inward, we find ourselves within the confines of our solar system, a cosmic oasis teeming with wonders. At its center lies the Sun, a brilliant sphere of plasma that sustains life on our planet and governs the intricate dance of the planets and moons that orbit it. The Sun's radiant energy, a product of thermonuclear fusion reactions, has shaped the celestial landscape we observe from Earth.Each planet in our solar system bears its unique characteristics, from the scorching temperatures of Mercury to the mesmerizing rings of Saturn. Jupiter, the gas giant, captivates us with its swirling storms, while Mars tantalizes our curiosity with its rusty hues and potential for harboring life. These celestial bodies serve as a testament to the diversity and complexity of our cosmic neighborhood.The Moon: Our Closest Celestial CompanionTurning our gaze skyward, we find the Moon, our closest celestial companion and a constant source of fascination. This natural satellite, forever locked in a gravitational embrace withEarth, has been a guiding light for sailors, a muse for poets, and a canvas for humanity's dreams of exploration.The Moon's cratered surface, etched by eons of cosmic bombardment, holds clues to the violent history of our solar system's formation. Its waxing and waning phases, governed by its intricate dance with Earth and the Sun, have shaped the tides and influenced countless cultural and religious traditions throughout human history.The Stars: Beacons in the NightFinally, we return to the stars, those brilliant points of light that have inspired awe and wonder since the dawn of humanity. Each star is a furnace of nuclear fusion, burning with an intensity that defies comprehension. From the scorching blue giants to the cool, red dwarfs, these celestial bodies represent the building blocks of the cosmos, forging the elements that make up our planet and ourselves.As we gaze upward, we are greeted by constellations, those celestial patterns that have guided travelers, sparked mythologies, and captured the imagination of cultures across the globe. The Big Dipper, Orion the Hunter, and countless others adorn the night sky, serving as celestial signposts in our cosmic journey.The stars hold within them the secrets of stellar evolution, from their birth in the dense clouds of interstellar gas and dust, to their eventual transformation into white dwarfs, neutron stars, or even the enigmatic black holes that lurk at the heart of galaxies.ConclusionAs we conclude our cosmic odyssey, we are reminded of the profound interconnectedness that binds us to the universe. The stars, galaxies, and celestial bodies that dot the night sky are not mere decorations but rather the manifestations of the fundamental laws that govern our existence.Through the tireless efforts of astronomers, astrophysicists, and space explorers, we inch ever closer to unraveling the mysteries that lie beyond our terrestrial confines. The celestial wonders that adorn the night sky serve as a constant reminder of the vastness of the cosmos and the boundless potential for discovery that awaits us.So, let us gaze upward, with wonder and curiosity, for in the stars, we find not only the answers to the deepest questions of our existence but also the inspiration to push the boundaries of human knowledge and exploration ever further.篇3The Brilliance of the Cosmos: A Journey Through the StarsAs I gaze up at the inky blackness of the night sky, a tapestry of twinkling lights unfolds before my eyes. These celestial beacons, scattered across the vast expanse of the cosmos, have captivated humanity since the dawn of time. From the most distant galaxies to the celestial bodies that grace our own cosmic neighborhood, the stars offer a gateway into the mysteries of the universe, igniting our curiosity and fueling our thirst for knowledge.Far Beyond Our Cosmic BackyardLet us embark on a journey that transcends the boundaries of our own Milky Way galaxy, venturing into the farthest reaches of the observable universe. Here, we encounter galaxies so distant that their light has traveled for billions of years before reaching our eyes. These cosmic metropolises, teeming with billions of stars, are but mere specks in the grand canvas of the cosmos.The Hubble Deep Field, a region of the sky no larger than a grain of rice held at arm's length, unveils a breathtaking tapestry of galaxies, each one a unique tapestry of stars woven togetherby the invisible threads of gravity. Some appear as elegant spirals, their arms gracefully unfurling into the void, while others take on the form of elliptical or irregular shapes, each a testament to the diversity of the universe.Quasars, the brilliant beacons powered by supermassive black holes at the hearts of distant galaxies, shine with an intensity that defies comprehension. Their light, emitted billions of years ago, serves as a cosmic lighthouse, guiding our understanding of the universe's earliest epochs and the processes that shaped the cosmos as we know it today.The Cosmic Web and the Birth of StarsAs we draw closer to our cosmic home, we encounter the intricate cosmic web – a vast, interconnected network of filaments composed of dark matter and gas. Within this web, matter accumulates, forming the seeds from which galaxies are born and stars ignite their brilliant fires.It is within these dense regions of the cosmic web that we witness the birth of stars, a process that unfolds over millions of years. Vast clouds of gas and dust, drawn together by gravity, collapse under their own weight, igniting nuclear fusion at their cores and giving birth to brilliant stellar furnaces that will illuminate the cosmos for billions of years.The stellar nurseries within our own Milky Way galaxy offer a glimpse into this celestial genesis. The Orion Nebula, a vast cloud of gas and dust visible to the naked eye, is a celestial nursery where thousands of stars are being born. Here, we can witness the raw materials of star formation – the swirling eddies of gas and dust, sculpted by the fierce winds and radiation from newly formed stars, painting a vivid picture of the cosmic cycle of birth and renewal.Our Galactic NeighborhoodAs we draw ever closer to our cosmic home, we encounter the stars that grace our own galactic neighborhood. The Milky Way, a vast spiral galaxy containing hundreds of billions of stars, stretches across the night sky like a celestial river, its misty band of light a testament to the countless stars that call it home.Within this cosmic city, we find a diverse array of stellar residents. The brilliant, blue-white stars burn with a ferocity that belies their relatively short lifespans, while the cooler, reddish stars smolder for billions of years, their steady glow a beacon of stability in the ever-changing cosmos.Among these stellar citizens, we find the familiar faces of our celestial neighbors. The North Star, Polaris, has guided travelers and explorers for millennia, its unwavering position a celestialcompass in the night sky. Sirius, the brightest star in the night sky, shines with a brilliance that outshines all others, its blue-white hue a testament to its searing temperatures.The Celestial Companions in Our Cosmic BackyardAs we draw ever nearer to our cosmic home, we encounter the celestial bodies that grace our own celestial backyard. The planets, those wandering worlds that have captivated our imaginations for centuries, offer a glimpse into the diversity of our solar system.From the scorched and cratered surface of Mercury to the gentle azure skies of Neptune, each planet is a unique world unto itself, shaped by the interplay of gravity, geology, and the relentless forces of the cosmos. We marvel at the towering storms of Jupiter, the rings of Saturn, and the icy mysteries of the outer solar system, each a testament to the incredible diversity that exists within our cosmic neighborhood.Yet, it is our closest celestial companion, the Moon, that holds a special place in our hearts. This ever-present orb, waxing and waning in the night sky, has been a constant companion to humanity throughout our existence. Its phases have guided our calendars, its movements have shaped our tides, and its crateredsurface bears witness to the cosmic impacts that have sculpted its landscape over billions of years.As we gaze upon the Moon's familiar face, we are reminded of our cosmic roots – born from the same primordial clouds of gas and dust that gave rise to the stars and planets. We are humbled by the realization that we are but tiny specks in the vast expanse of the cosmos, yet we are inextricably linked to the celestial tapestry that surrounds us.The Journey ContinuesAs I stand beneath the brilliant tapestry of the night sky, my journey through the stars has only just begun. With each new discovery, each new revelation, our understanding of the cosmos deepens, and our sense of wonder grows. The stars, those celestial beacons that have guided humanity for millennia, continue to beckon us, inviting us to explore the mysteries that lie beyond the boundaries of our cosmic backyard.It is a journey that transcends time and space, a quest to unravel the secrets of the universe and to understand our place within the grand cosmic tapestry. And as we gaze upon the stars, we are reminded that we are all travelers on this cosmic journey, united by our shared sense of awe and our unquenchable thirst for knowledge.。
Unit_1(1)
地理专业英语
教材参考
作/译者：余中元 出版社：西南交通 大学出版社 出版日 期：2008年12月
http://www.physical /
Physical Geography
自然地理篇
Human Geography 人文地理篇 Physical Geography 自然地理篇 Human Geography Technology Geography 技术地理篇
Unit 1 The Earth and the Universe Text: The Jovian Planets
Jupiter, Saturn, Uranus, and Neptune are known as the Jovian (Jupiter-like) planets, because they are all gigantic compared with Earth，and they have a gaseous nature like Jupiter’s. The Jovian planets are also referred to as the gas giants, although some or all of them might have small solid cores.
Unit 1 The Earth and the Universe Text: The Terrestrial Planets
The terrestrial planets are the four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrials because they have a compact, rocky surface like the Earth’s. The planets, Venus, Earth and Mars have significant atmospheres while Mercury has almost none.
托福阅读真题第17套
第17套Determining the Ages of the Planets and the UniverseParagraph1The planets of our solar system all revolve around the Sun in the same direction and in orbits that lie in nearly the same plane.This is strong evidence that the planets formed simultaneously from a single disk of material that rotated in the same direction as the modern planets.Paragraph2Precisely when the planets came into being has been a difficult issue to resolve.While Earth’s water is necessary for life,its abundance near the planet’s surface makes rapid erosion inevitable.Continuous alteration of the crust by erosion and also by igneous (volcanic)and metamorphic(pressure and heat within Earth)processes makes unlikely any discovery of rocks nearly as old as Earth.Thus geologists have had to look beyond this planet in their efforts to date Earth’s origin.Fortunately,we do have samples of rock that appear to represent the primitive material of the solar system. These samples are meteorites,which originate as extraterrestrial objects,called meteors,that have been captured in Earth’s gravitational field and have then crashed into our planet.1.According to paragraphs1and2,what evidence leads astronomers to believe thatall the planets formed at approximately the same time?Samples of rocks from all the planets are the same age.All the planets orbit the Sun in the same direction and in about the same plane.All planets have the same igneous and metamorphic processes.The gravitational field of each planet is about the same strength. Paragraphs1and2are marked with arrows[→]2.The word”inevitable”in the passage is closet in meaning tocontinuousobviouscertaineasy3.Which of the following is NOT mentioned in paragraph2as a cause of constantchange to Earth’s crust?WaterIgneous processesMetamorphic processesMeteoritesParagraph2is marked with an arrow[→]Paragraph3Some meteorites consist of rocky material and,accordingly,are called stony meteorites.Others are metallic and have been designated iron meteorites even though they contain lesser amounts of elements other than iron.Still others consist of mixtures of rocky and metallic material and thus are called stony-iron meteorites. Meteors come in all sizes,from small particles to the small planets known as asteroids; no asteroid,however,has struck Earth during recorded human history.Many meteorites appear to be fragments of larger bodies that have undergone collisions and broken into pieces.Iron meteorites are fragments of the interiors of these bodies, comparable to Earth’s core,and stony meteorites are from outer portions of these bodies,comparable to Earth’s mantle(the layer between the core and outer crust).4.The word”accordingly”in the passage is closet in meaning tocorrespondinglyfrequentlyinterestinglyinformally5.Which of the following can be inferred from paragraph3about meteorites?Their composition can help determine the part of the larger body from which they broke off.They are difficult to distinguish from rocks in Earth’s mantle.Their collisions with Earth have become more frequent than in the past.They are older than the rest of the solar system.Paragraph3is marked with an arrow[→]6.According to paragraph3,which of the following is a characteristic of asteroids? They are the largest meteors.They are made mostly of iron and other metals.They often collide with Earth.They are the oldest meteors.Paragraph3is marked with an arrow[→]Paragraph4Meteorites have been radiometrically dated by means of several decay systems, including rubidium-strontium,potassium-argon,and uranium-thorium.The dates thus derived tend to cluster around4.6billion years,which suggests that this is the approximate age of the solar system.After many meteorites had been dated,it was gratifying to find that the oldest ages obtained for rocks gathered on the surface of the Moon also were approximately4.6billion years.This must,indeed,be the age of the solar system.Ancient rocks can be found on the Moon because the lunar surface, unlike that of Earth,has no water to weather and erode rocks and is characterized by only weak movements of its crust.7.Which of the following can be inferred from paragraph4about the radiometricdating of meteorites?Scientists tried several different radiometric systems before finding one that worked.The radiometric dating of different meteorites produced similar results.Many meteorites were damaged by the radiometric dating.Radiometric dating was not as accurate as scientists expected.Paragraph4is marked with an arrow[→]8.The word”cluster”in the passage is closet in meaning toapproachspreadgroupvary9.According to paragraph4,why are scientists confident that the age of the oldestmeteorites they studied is also the age of the solar system?Radiometric dating has been proven to be reliable.The oldest rocks found on the surface of the Moon are the same age as the meteorites.No meteorites have been found that are younger than4.6billion years old.Meteorites on the Moon are the same age as those on other planets. Paragraph4is marked with an arrow[→]Paragraph5Determining the age of the universe has been more complicated.Most stars in the universe are clustered into enormous disk-like galaxies.The distance between our galaxy,known as the Milky Way,and all others is increasing.In fact,all galaxies are moving away from one another,evidence that the universe is expanding.It is not the galaxies themselves that are expanding but the space between them.What is happening is analogous to inflating a balloon with small coins attached to its surface. The coins behave like galaxies:although they do not expand,the space between them does.Before the galaxies formed,matter that they contain was concentrated with infinite density at a single point from which it exploded in an event called the big bang.Even after it assembled into galaxies,matter continued to spread in all directions from the site of the big bang.10.The word”enormous”in the passage is closet in meaning toexpandingvery brightdistanthuge11.Why does the author refer to“inflating a balloon with small coins attached to itssurface”?To help explain how the universe can expand while the galaxies remain the same sizeTo imply that the universe must eventually stop expandingTo support the statement that most stars are found in disk-shaped galaxiesTo help explain how the universe began as a single point of dense matterParagraph6The evidence that the universe is expanding makes it possible to estimate its age.This evidence,called the redshift,is an increase in the wavelengths of light waves traveling through space—a shift toward the red end of the visible spectrum of wavelengths. Expansion of the space between galaxies causes this shift by stretching light waves as they pass through it.The farther these light waves have traveled through space,the greater the redshift they have undergone.For this reason,light waves that reach Earth from distant galaxies have larger redshifts than those from nearby galaxies. Calculations based on these redshifts indicate that about13.7billion years ago all of the galaxies would have been at one spot,the site of the big bang.This,then,is the approximate date of the big bang and the age of the universe.12.According to paragraph6,how did astronomers learn that the universe isexpanding?By measuring the distance between galaxiesBy observing the movement of stars within galaxiesBy studying the wavelengths of light from distant galaxiesBy comparing the sizes of different galaxiesParagraph6is marked with an arrow[→]Paragraph3■Some meteorites consist of rocky material and,accordingly,are called stony meteorites.■Others are metallic and have been designated iron meteorites even though they contain lesser amounts of elements other than iron.■Still others consist of mixtures of rocky and metallic material and thus are called stony-iron meteorites.■Meteors come in all sizes,from small particles to the small planets known as asteroids;no asteroid,however,has struck Earth during recorded human history. Many meteorites appear to be fragments of larger bodies that have undergone collisions and broken into pieces.Iron meteorites are fragments of the interiors of these bodies,comparable to Earth’s core,and stony meteorites are from outer portions of these bodies,comparable to Earth’s mantle(the layer between the core and outer crust).13.Look at the four squares[■]that indicate where the following sentence could beadded to the passage.Several varieties of meteorites have been observed.Where would the sentence best fit?Click on a square[■]to add the sentence to the passage.14.Directions:An introductory sentence for a brief summary of the passage isprovided plete the summary by selecting the THREE answer choices that express the most important ideas in the passage.Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.This question is worth2points.Drag your choices to the spaces where they belong.To review the passage,click onView Text.Answer ChoicesA.Determining the age of the planets by examining rocks on Earth is difficult because Earth’s crust is constantly changing.B.Meteorites found on Earth and rocks from the Moon’s surface are the best evidence for estimating the age of the planets.C.The expansion of the universe makes it possible to estimate its age by measuring the amount of the redshift of light coming from distant galaxies.D.All three kinds of meteorites are similar in composition to Earth in that they have an inner core,a rocky mantle,and an outer crust.E.Radiometric dating of meteorites recovered from the Moon shows that they are older than those that are found on Earth.F.The redshift phenomenon measures the rate at which the stars in a galaxy are moving away from each other.Costs and Benefits of Dispersal（17年上半年再次考过）Paragraph1In order to move from one home base to another,animals must expend calories not only while moving but even before the dispersal when they invest in the development of the muscles needed to move.For example,if a cricket is to leave a deteriorating environment and move to a new and better place,it will need large flight muscles to fly away.Presumably,the calories and materials that go into flight muscle development and maintenance have to come out of the general energy budget of the animal.This means that other organ systems cannot develop as rapidly as they could otherwise,which may mean that the flight-capable individual is,in some other respects,less fit to survive.1.The word”Presumably”in the passage is closet in meaning toIt is reasonable to assumeIt is possibleIt can be arguedIt is certainly true2.In paragraph1,the discussion of cricket dispersal is used to illustrate which of thefollowing principles?For dispersing animals,the benefits of dispersal exceed the costs.Dispersal always involves costs for the dispersing animal.Only animals with the greatest fitness for survival are able to disperse.Dispersal,as much as organ development,requires energy.Paragraph1is marked with an arrow[→]Paragraph2Dispersing individuals not only have to pay energetic,developmental,and travel costs but are also more often exposed to predators—all of which raises the question,why are animals so often willing to leave home even when this means leaving a familiar, resource-rich location?This question is particularly pertinent for species in which some individuals disperse while others do not or do not disperse as far.One species in which some individuals travel farther than others is Belding’s ground squirrel.Young male squirrels travel about150meters from the burrow in which they were born, whereas young females usually settle down only50meters or so from where they were born.Why should young Belding’s ground squirrels disperse at all,and why should the males disperse farther than their sisters?3.The word”pertinent”in the passage is closet in meaning topuzzlingimportantcomplexrelevant4.According to paragraph2,what is of particular interest about the dispersal ofBelding’s ground squirrels?Young squirrels disperse farther than adults.Young squirrels disperse even from resource-rich areas.The males and females have different patterns of dispersal.They leave the mother’s burrow at an earlier age than other squirrels. Paragraph2is marked with an arrow[→]5.It can be inferred from paragraph2that the phenomenon of dispersalis difficult to observe in the wildoccurs for reasons that are not always immediately apparentis motivated by the desire to obtain more or better resourceshas few benefits for most speciesParagraph2is marked with an arrow[→]Paragraph3According to one argument,dispersal by juvenile animals of many species may be an adaptation against problems associated with inbreeding.When two closely related individuals mate,their offspring are more likely to manifest genetic diseases than are the offspring of genetically unrelated individuals,and as a result,inbreeding tends to produce animals that are less likely to survive to adulthood and reproduce.Dispersal of juveniles makes inbreeding less likely.6.Which of the sentences below best expresses the essential information in thehighlighted sentence in the passage?Incorrect choices change the meaning in important ways or leave out essential information.When closely related individuals mate,their offspring are likely to manifest genetic diseases that will probably be passed on to the next generation.Genetic diseases inherited from parents that are not related make it less likely that the affected offspring will survive to adulthood and reproduce.When two related individuals mate,their offspring may survive to adulthood,but they are unlikely to reproduce.There is a tendency for the offspring of closely related parents to have genetic diseases that make it less likely they will survive and reproduce.Paragraph4If avoidance of inbreeding is the point of dispersing,then one might expect as many female ground squirrels as males to travel150meters from their natal burrow.In fact females do not disperse as far as males,perhaps because the costs and benefits of dispersal differ for the two sexes.It has been suggested that the reproductive success of female Belding’s ground squirrels depends on their possession of a territory in which to rear their young.Female ground squirrels that remain near their birthplace enjoy assistance from their mothers in the defense of their burrows against rival females.Thus,the benefits of remaining on familiar ground are greater for females than for males.7.According to paragraph4,young female Belding’s ground squirrels may remaincloser to where they were born than do males in order toavoid inbreeding with their male siblingsavoid competition with other females for territorysave energy they need to defend their burrowsbenefit from their mothers’helpParagraph4is marked with an arrow[→]Paragraph5There may,however,be another reason why male mammals disperse greater distances than females.The usual rule is that males,not females,fight with one another for access to mates,and,therefore,males that lose such conflicts may find it advantageous to move away from same-sex rivals that they cannot subdue.Although this hypothesis probably does not apply to Belding’s ground squirrels,since young males have not been seen fighting with older ones around the time of dispersal,the idea is more plausible with respect to some other species,such as lions.8.According to paragraph5,the hypothesis that males disperse as a result ofconflicts with other males is not supported in the case of Belding’s ground squirrels becauseyoung male squirrels that lose fights to other males do not disperseunlike most species,it is the females,not the males,that fight with each otherthere is no evidence that young male squirrels fight with other males before dispersingfights between males generally take place after the males have dispersed Paragraph5is marked with an arrow[→]9.The word”subdue”in the passage is closet in meaning toremovefightdefeatacceptParagraph5There may,however,be another reason why male mammals disperse greater distances than females.The usual rule is that males,not females,fight with one another for access to mates,and,therefore,males that lose such conflicts may find it advantageous to move away from same-sex rivals that they cannot subdue.Although this hypothesis probably does not apply to Belding’s ground squirrels,since young males have not been seen fighting with older ones around the time of dispersal,the idea is more plausible with respect to some other species,such as lions. Paragraph6Lions live in large groups,or prides,from which young males disperse.In contrast, the daughters of the resident lionesses usually spend their entire lives close to where they were born.The sedentary females benefit from their familiarity with good hunting grounds and safe breeding dens in their natal territory,among other things. The departure of many young male lions coincides with the arrival of new mature males that violently displace the previous masters of the pride and chase off the males that are not yet adults in the pride as well.These observations support the mate-competition hypothesis for male dispersal.However,if young males are not evicted after a pride takeover,they often leave anyway without any coercion from adult males and without ever having attempted to mate with their female relatives.Moreover,mature males that have claimed a pride sometimes disperse again, expanding their range to add a second pride of females,at a time when their daughters in the first pride are becoming sexually mature.Inhibitions against inbreeding apparently exist in lions and cause males to leave home.10.According to paragraphs5and6,the patterns of dispersal in Belding’s groundsquirrels and lions are similar in which of the following ways?Young males are forced to disperse by older males.Avoiding inbreeding is probably not a factor in the explanation of the pattern of dispersal.Males disperse when new siblings are born.The males disperse farther than the females.Paragraphs5and6are marked with arrows[→]11.The phrase”coincides with”in the passage is closet in meaning tois driven byoccurs at the same time asmakes possibleis a sign of12.Why does the author provide the information that“if young males are not evictedafter a pride takeover,they often leave anyway without any coercion from adult males and without ever having attempted to mate with their female relatives”?To support the conclusion that made lions disperse to find mates to which they are not closely relatedTo indicate that the mate-competition hypothesis does not fully account for the dispersal of young male lionsTo imply that young male lions voluntarily leave a pride that has been taken over because the adult males prevent them from mating within the prideTo indicate that males,not females,leave a pride after it has been taken over by adult malesParagraph4■If avoidance of inbreeding is the point of dispersing,then one might expect as many female ground squirrels as males to travel150meters from their natal burrow.■In fact females do not disperse as far as males,perhaps because the costs and benefits of dispersal differ for the two sexes.■It has been suggested that the reproductive success of female Belding’s ground squirrels depends on their possession of a territory in which to rear their young.■Female ground squirrels that remain near their birthplace enjoy assistance from their mothers in the defense of their burrows against rival females.Thus,the benefits of remaining on familiar ground are greater for females than for males.13.Look at the four squares[■]that indicate where the following sentence could beadded to the passage.However,inbreeding can be avoided without both males and their female relatives dispersing the same distance.Where would the sentence best fit?Click on a square[■]to add the sentence to the passage.14.Directions:An introductory sentence for a brief summary of the passage isprovided plete the summary by selecting the THREE answer choices that express the most important ideas in the passage.Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.This question is worth2points.Drag your choices to the spaces where they belong.To review the passage,click onView Text.Answer ChoicesA.There are a number of competing explanations of why animals disperse,but none of them is consistent with all the observed patterns of dispersal.B.The reason there is little inbreeding among lions is that young males are driven away from their female relatives by the adult males who forcibly take over a lion pride.C.Inbreeding significantly lowers the likelihood that offspring will survive,and so avoiding inbreeding is a significant benefit of dispersal.D.Since males of most species must establish a territory for mating,dispersing of the males makes it more likely that most males will be able to reproduce.E.There need to be significant benefits for a species to disperse because the requirements of dispersal involve energy costs and dangers for the dispersing individuals.F.In mammal species,young males often leave their family group while related females benefit from remaining in close association with each other and their birthplace.The Multiplier EffectParagraph1The causes behind the rapid development of the Minoan and Mycenaean civilizations in the Aegean during the late third and second millennia B.C.E.have intrigued scholars for years.Until recently,most explanations attributed Aegean development tooutside influence.Civilization had emerged in Mesopotamia by3000B.C.E,and, some archeologists argued,Mesopotamian trade introduced civilized ideas and technological innovations into nearby,less advanced areas.Others hypothesized that civilization was brought to the Aegean by invasion from some adjacent region,of which Anatolia in modern Turkey seemed the most plausible.1.Paragraph1implies which of the following about traditional scholarshipconcerning the development of Aegean civilizations?It focused on the influence of Aegean trade on more advanced civilization rather than the invasion of the Aegean by a technologically advanced culture.The development of Minoan civilization was thought to require a different explanation from that for the development of Mycenaean civilization.It maintained that the rapid development of Aegean civilization could be explained only through external influence.There was general agreement that Anatolia and Mesopotamia were both responsible for the development of civilization in the Aegean.Paragraph1is marked with an arrow[→]Paragraph2In a work published in1972,Professor Colin Renfrew approached the problem from a different viewpoint.He argued that the scanty available evidence for invasion or immigration from Anatolia into Greece in the early Bronze Age(about3300-2200 B.C.E.)showed that,at most,such incursion was limited,and that it could not be regarded as responsible for the transformation of society there.Trade,though clearly documented,was also an inadequate explanation in itself.To understand the major changes in social organization and complexity that took place,it was necessary,said Renfrew,to determine the impact that new variables emerging in the early Bronze Age may have had on every interrelated aspect of the local social system.The two new major developments he considered were changes in the subsistence economy and the introduction of bronze metallurgy.2.Which of the sentences below best expresses the essential information in thehighlighted sentence in the passage?Incorrect choices change the meaning in important ways or leave out essential information.Renfrew said that local variables affected the complex social organization of the early Bronze Age.Renfrew said that the major changes in social organization could be understood only by examining the effects of the new developments that took place in the early Bronze Age.The early Bronze Age,Renfrew said,was a time in which there were major changes to many interrelated aspects of local social systems.To understand the social organization and complexity of the early Bronze Age,it was necessary,said Renfrew,first to determine what new variables had emerged.Paragraph3The economy of Neolithic Greece was based on growing grains and raising sheep. Early in the third millennium B.C.E.,cultivation of grape vines and olive trees also became important in southern Greece and the Aegean Islands.Both crops were eminently suitable for trade and storage in the form of olive oil and wine.They were grown on land that was not suitable for grain farming.Their cultivation required work at a different time of year from that needed by grain crops,and much of this work, such as harvesting,was relatively light.As a result,agricultural yields were substantially increased without disrupting established agricultural practice.That increase in turn allowed,or stimulated,population growth.For the first time there was enough demand for specialized crafts and services to justify the existence of full-time craftspeople,who could be supported from the extra agricultural output.3.The word”justify”in the passage is closet in meaning toinclude within the social systemprovide a rational basis foremployencourage4.According to paragraph3,growing grape vines and olive trees increasedagricultural yields becausegrapes and olives were mostly used for trade rather than for competing with established crops in local marketsgrape vines and olive trees could be cultivated on land that was also used for raising sheepgrowing grapes and olives did not require the services of specialized workersgrape vines and olive trees did not compete with other crops for land or labor Paragraph3is marked with an arrow[→]5.According to paragraph3,the increased importance of grape and olive cultivationled to which of the following changes in Greece?An increase in the number of inhabitantsAn increase in the amount of grain tradedAn increase in the percentage of farmers in the populationThe development of new methods of storing foodsParagraph3is marked with an arrow[→]Paragraph4Some copper artifacts were made during the fourth millennium B.C.E,but there were not many of them and they had little economic or social significance.When,in the third millennium,copper began to be mixed with tin to produce the relatively hard alloy bronze,demand for metal goods grew.Bronze could be used to make a range of useful new tools and weapons and a variety of impressive ornaments.The demand for metalwork stimulated further specialization in crafts such as toolmaking and jewelrymaking.The new tools promoted the development of other crafts,like carpentry and petition for prestigious or useful craft products and for control of their producers helped to heighten both social differences within communities and conflicts between them,resulting in the emergence of local chieftains,who were also in many instances warriors.These chieftains regulated agricultural and craft production,operating a distribution system through which the farmers could obtain tools or ornaments they needed or wanted.The organizational demands of controlled distribution made it necessary to develop methods of measurement and recording, which led to the development of writing.6.The word”promoted”in the passage is closet in meaning torequiredbenefited fromencouragedspeeded up7.According to paragraph4,why did the invention of bronze lead to increasedconflict?It resulted in more effective weapons for warriors.It led to competition for the control of skilled craftspeople and their products.It left the craftspeople who had been involved in making copper products without and occupation.It led to competition for available supplies of tin to be used in the production of bronze.Paragraph4is marked with an arrow[→]8.All of the following are discussed in paragraph4as changes in Greek society afterbronze was introduced EXCEPT:Social differentiation within communities increased.Metalcraft workers became more specialized.Methods were invented for documenting the distribution of goods.Craft workers gained greater independence from local chieftains.Paragraph4is marked with an arrow[→]Paragraph5Renfrew argued that any single innovation would have had a limited or negligible effect on social organization because the inherently conservative nature of societies acts to minimize change.However,the interaction of several simultaneous developments created a multiplier effect.In the Aegean,increased agricultural productivity provided the means to support craft specialization,while bronze metallurgy provided the technology for producing highly valued new products.These factors set in motion a series of changes in other subsystems of society.Those changes in turn resulted in what,in a term borrowed from electronics,are called positive feedback loops—alterations in the workings of a social system that serve to reinforce。
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arXiv:astro-ph/0312550v1 19 Dec 2003DraftversionFebruary2,2008PreprinttypesetusingLATEXstyleemulateapjv.9/08/03
ADISKGALAXYOFOLDSTARSATZ∼2.51AlanStocktonInstituteforAstronomy,UniversityofHawaii,2680WoodlawnDrive,Honolulu,HI96822
GabrielaCanalizoInstituteofGeophysicsandPlanetaryPhysicsandDepartmentofEarthSciences,UniversityofCalifornia,Riverside,CA95521
ToshinoriMaiharaDepartmentofAstronomy,KyotoUniversity,Kitashirakawa-Oiwake-cho,Sakyo-ku,Kyoto606-8502,JapanDraftversionFebruary2,2008
ABSTRACTWedescribeobservationsofagalaxyinthefieldofthez=2.483radiogalaxy4C23.56,photometri-callyselectedtohaveaspectral-energydistributionconsistentwithanoldstellarpopulationattheredshiftoftheradiogalaxy.Explorationofredshift—stellar-population—reddeningconstraintsfromthephotometryindicatesthatthegalaxyisindeedataredshiftclosetothatof4C23.56,thattheageofthemostrecentsignificantstarformationisroughly2Gyr,andthatreddeningisfairlymodest,withmorereddeningrequiredfortheyoungerendofstellaragerange.Fromanalysisofadeepadaptive-opticsimageofthegalaxy,wefindthatanr1/4-lawprofile,commonforlocalspheroidalgalaxies,canbeexcludedquitestrongly.Ontheotherhand,apureexponentialprofilefitsremarkablywell,whilethebestfitisgivenbyaS´ersicprofilewithindexn=1.49.Reconstructionofthetwo-dimensionalformofthegalaxyfromthebest-fitmodelisconsistentwithadiskgalaxywithneitherasignificantbulgecomponentnorgrossazimuthalstructure.Theassemblyofroughly2L∗ofoldstarsintosuchaconfigurationthisearlyinthehistoryoftheuniverseisnoteasilyexplainablebyanyofthecurrentlypopularscenariosforgalaxyformation.Agalaxywiththesepropertieswouldseemtorequiresmoothbutrapidinfallofthelargemassofgasinvolved,followedbyaburstofextremelyvigorousandefficientstarformationintheresultingdisk.Subjectheadings:galaxies:high-redshift—galaxies:formation—galaxies:evolution
1.INTRODUCTION
Ourunderstandingofthemechanismsandtimescalesoftheformationoftheveryfirstluminousgalaxiesintheuniverseisstillveryuncertain.Manydetailedstud-iesoflocalluminousearly-typegalaxiesfavorformationatveryearlyepochsandwithinaveryshorttimespan(e.g.,Peebles2002andreferencestherein).Inparticular,theαelementsareenhancedinluminousellipticalsrel-ativetoFe(e.g.,Worthy,Faber,&Gonz´alez1992),thisenhancementisstronglycorrelatedwiththecentralve-locitydispersionσ(Trageretal.2000),andtherelationissimilarforfieldandclusterellipticals(Bernardietal.1998;Collessetal.1999;Thomas,Maraston,&Bender2002).Galaxieswiththeoldeststellarpopulationsareboththemostluminousandthemostαenhanced(Thomas,Maraston,&Bender2002).Iftheseclaimsarevalid,themostluminousgalaxiesformedwithinaquiteshortperiodveryearlyinthehistoryoftheuni-verse,lessluminousearly-typegalaxiesformedmoregraduallyandsomewhatlater,anddifferencesinstarformationhistoriesbetweenellipticalsinthefieldand
1BasedinpartondatacollectedatSubaruTelescope,which
isoperatedbytheNationalAstronomicalObservatoryofJapan.SomeofthedatapresentedhereinwereobtainedattheW.M.KeckObservatory,whichisoperatedasascientificpartnershipamongtheCaliforniaInstituteofTechnology,theUniversityofCaliforniaandtheNationalAeronauticsandSpaceAdministration.TheOb-servatorywasmadepossiblebythegenerousfinancialsupportoftheW.M.KeckFoundation.
thoseinclustersarerelativelyminor.Thislaststate-mentisalsosupportedbyfundamental-planeanaly-ses(e.g.,vanDokkum&Ellis2003;Treuetal.2001;butseealsoTreuetal.2002).Suchconclusionsap-peartobedifficulttoreconcilewithstandardin-terpretationsoftheresultsofthesemi-analyticcold-dark-matter(CDM)models(e.g.,Thomas&Kauffmann1999;Kauffmann&Haehnelt2000),whichpredictthat,forthecurrentlyfavoredlow-densitycosmology(H0∼70,Ωm∼0.3,Ωvac∼0.7;assumedthroughoutthispaper),mostofthepresent-daybrightellipticalswillhaveundergonefinalassemblybetweenz=1andz=2.However,thereareatleasttwocaveatstothisstatement:(1)Oneoftheleastcertainpartsofthesemi-analyticCDMmodelsisthetreatmentofstarfor-mationandresultingfeedbackeffects,anditispossi-blethatdifferentassumptionsinthisareacouldmiti-gateatleastsomeofthediscrepancy;and(2)assem-blyatrelativelylowredshiftsisnotnecessarilyincon-sistentwithformationofmostofthestarsatmuchhigherredshifts.Nevertheless,boththecolor-luminosityrelationshipforspheroids(Bower,Lucey,&Ellis1992;Ellisetal.1997;vanDokkumetal.2000)andthecor-relationofα-elementenhancementwithluminosityshowthattheformationofthestellarpopulationandtheas-semblyofthegalaxycannotbecompletelyindependentprocesses.AsPeacock(1999)hassuccinctlyputit,“Itseemsasifthestarsinellipticalswereformedatatimewhenthedepthofthepotentialwellthattheywould