【thatll】iBT备考日志

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【听力---SSS---April 27, 2009】

More Fronts（战线，阵线） in Fight against Malaria（疟疾）
World Malaria Day brought awareness of the unorthodox（非传统的） biomedical ideas that are joining the search for a vaccine.

April 25th was World Malaria Day. The mosquito-borne（蚊传播的） disease is still one of the biggest killers in developing countries with a death toll of a million each year. But there’s an international push for a multi-front war on malaria, ranging from cheap and effective bed netting to the development of a vaccine. The Gates Foundation has bet on vaccines, but is also funding less conventional scientific approaches.

For example, a scientist at Colorado State University is working on making human blood a mosquito killer. Some drugs already distributed in the developing world to combat parasites such as hookworm are also toxic to the malaria-transmitting Anopheles mosquito. The mosquito bites, and the drug in the blood kills it. Researchers are investigating how this approach could be applied and expanded.

Another team from the University of Washington discovered that the malaria parasite in Asia outsmarts（比什么更聪敏） drugs and develops resistance much more quickly than in other parts of the world. They’ve been investigating the mechanism of action to be able to figure out a way to block that resistance.
There is hope: in recent years, the Maldives, Tunisia and the United Arab Emirates have eliminated malaria.

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【听力---SSS---April 28, 2009】

Handedness Could Reveal Aliens
Researchers at the National Institute of Standards and Technology are developing a way to measure the directionality of compounds on other planets--which could reveal the presence of life, because biomolecules tend to twist in only one of two possible directions.

Many of the key molecules for life have a specific direction, or handedness: DNA twists to the right, amino acids to the left. Now scientists at the National Institute of Standards and Technology (or NIST) aim to take advantage of this so-called chirality（手性） to search for signs of extraterrestrial life.

When chemists synthesize organic compounds in the lab, they often wind up with a mix of molecules: half are right-handed, and half are left. But cells are a bit more particular. When life arose, our ancestors made some choices. They went with the right-handed sugars, and the left-handed amino acids, a tradition still in effect.

The scientists at NIST have come up with a gadget that can see the polarized light that bounces off of molecules that show a preferred handedness. And in the Proceedings of the National Academy of Sciences, they report using the device to detect the signature reflection that comes from the chlorophyll in plant leaves. If this handedness meter works well at a distance, they could load it onto a space probe—a preponderance of right- or left-handed biomolecules could mean a planet has at least simple life forms on it. And we might even find out if ET is a southpaw.

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【听力---SSS---April 29, 2009 】

Figuring Out Movies You'd Really Like
Netflix is offering $1 million to any group that can improve its user recommendations accuracy 10 percent, according to the May issue of IEEE Spectrum.

Netflix isn’t satisfied with the way its system recommends new movies to customers based on their viewing habits. So the mail-order DVD rental company has offered outside teams prizes to improve its accuracy. A group from AT&T Laboratories has already won $50,000 for figuring out a formula that’s 8.43 percent better at telling a film buff what to rent. And Netflix is sweetening the pot（增加堵住，冒更大的风险）—the team that can improve recommendation accuracy by 10 percent will get a cool million.

Also, sweeten the pot or deal. Make something financially more attractive, as in I am unable to give you the new title but I could sweeten the kitty a little by giving you a raise. This idiom comes from card games such as poker, where it means "add money to the pool," and uses sweeten in the sense of "make more agreeable." [Slang; c. 1900]

The contest requires that recommendations be made using the ratings customers give other movies they’ve rented. But the researchers say whether or not a person explicitly rates their returns, their rental history can be used as an “inferred rating” of things like genres or actors. What’s more, the preferences of other customers can predict how someone with similar rental histories would score a film. The research is explained in the May issue of the journal IEEE Spectrum.

There are certainly bigger problems to solve these days than recommending movies. But it would be nice to know why Netflix keeps insisting after I’ve returned Slumdog Millionaire and Delicatessen that I’d really like Annie.

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【听力---SSS---May 1, 2009】

Monkey Drives Dinosaur Game Extinct
A game recalled（召回） due to excessive lead（名词，读[led]，意为铅） in a monkey figure pits humans and monkeys against dinosaurs（pit against表示使与什么相斗）, which violates, well, so many things.

The U.S. Consumer Product Safety Commission and DND Imports of Los Angeles recently announced a voluntary recall of something called the Dinosaur Era 2 Hunting Dinosaur playset. Because the monkey contained too much lead. Yes, the monkey. Each set includes a dinosaur. A helicopter. Trees. A hunter. A monkey. And various hunting equipment.

Clearly, time travel is involved. Because how else do you have this particular assortment（聚集） of organisms in the same place, outside of a creationism museum? Now, if I were a time-traveling hunter looking to live out Ray Bradbury’s story A Sound of Thunder, and bag a dinosaur way back when, I wouldn’t bring a monkey. What’s he going to do, carry the guns? Really bad lesson for the kids. Maybe the idea is to shoot the dinosaur from the helicopter. Which leaves the monkey as the pilot. Another terrible example for children. Seriously, if they ever invent a time machine, they should slap a big warning label on it that says, CAUTION, NO MONKEYS. Also a good policy for DND Imports.

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【听力---SSS---May 4, 2009】

Earth Experiencing "Climates" Change?
A study in the journal Science finds that the Northern and Southern hemispheres may be undergoing climate change in distinct ways.

Climate change is the great environmental challenge facing the world today. But maybe we should start calling it “climates change”. Because scientists who’ve looked to glaciers to study the history of climate on Earth have found that the Northern and Southern hemispheres have not been moving in sync.

As you might imagine, glaciers are sensitive to changes in temperature. So scientists interested in the evolution of earth’s climate use these icy formations to gauge local conditions from the past. A research team used a newfangled method for measuring rare isotopes to accurately date glaciers in New Zealand. They then compared these numbers to historic records from the Northern Hemisphere. And they found no correlation in the growth of glaciers above and below the equator over the past 7,000 years. While the vast majority of glaciers are now in retreat, a few down under have been growing and shrinking like a bunch of yo-yo dieters.

The discovery, published in the May 1 issue of Science, suggests that the Earth’s climate doesn’t act as a single entity, but can vary from region to region. Which would make certain glaciers, whether or not they wither, better long-term weather bellwethers.

地球正在经历“多种气候”变化吗？
2009-05-11 10:54:22 作者：刘丰祎（译） 来源：新东方
A study in the journal Science finds that the Northern and Southern hemispheres may be undergoing climate change in distinct ways.
发表在《科学》（Science）杂志上的一项研究发现，北半球和南半球可能正在以截然不同的方式经历气候变化。

Earth Experiencing "Climates" Change?

Climate change is the great environmental challenge facing the world today. But maybe we should start calling it “climates change”. Because scientists who’ve looked to glaciers to study the history of climate on Earth have found that the Northern and Southern hemispheres have not been moving in sync.

As you might imagine, glaciers are sensitive to changes in temperature. So scientists interested in the evolution of earth’s climate use these icy formations to gauge local conditions from the past. A research team used a newfangled method for measuring rare isotopes to accurately date glaciers in New Zealand. They then compared these numbers to historic records from the Northern Hemisphere. And they found no correlation in the growth of glaciers above and below the equator over the past 7,000 years. While the vast majority of glaciers are now in retreat, a few down under have been growing and shrinking like a bunch of yo-yo dieters.

The discovery, published in the May 1 issue of Science, suggests that the Earth’s climate doesn’t act as a single entity, but can vary from region to region. Which would make certain glaciers, whether or not they wither, better long-term weather bellwethers.

地球正在经历“多种气候”变化吗？

目前全球面临的最大环境挑战就是气候变化。但是我们可能应该开始称之为“多种气候变化”，这是因为科学家们发现北半球和南半球的气候变化并不是同步的，这些科学家们通过研究冰川来研究地球的气候历史从而得到上述发现。

你可能想象的出来，冰川对气温的变化很敏感。所以对地球的气候演变感兴趣的科学家们利用过去冰川的形成来判断目前的情况。一个研究小组使用一种新奇的方法来测量稀有同位素的含量，从而准确地的推测出位于新西兰的冰川年代。然后他们把这些数据与来自北半球的历史记录做了比较。他们发现在过去的7000年时间里，赤道两边半球的冰川成长没有相关性。虽然目前大量的冰川在消退，但是在赤道以南也有少量的冰川在不停的增长和缩小，这就像大量节食瘦身的人们一样，不断地经历体重增加和减少。

这项研究发表在5月1日的《科学》（Science）杂志上，该研究表明，地球的气候并不是一个单一的“实体”，而是因地域的不同而变化多端，这可能使得一些冰川——不管这些冰川消退与否——可以成为更好的长期气候标志。

Vocabulary:

Hemisphere：半球
Distinct：显著的
Environmental: 环境的
Glacier: 冰川
In sync: 同步
Sensitive: 敏感的
Evolution: 演变；渐进
Gauge: 测量
Newfangled: 新奇怪异的
Isotope: 同位素
Accurately: 准确地
Correlation: 相关
Equator:赤道
Vast: 大量的
Majority: 大多数
Retreat: 减退
Shrink: 缩小
Bunch: 大量；大批；（口语）群体
Yo-yo: 游游(一种玩具, 用绳拽着能忽上忽下移动)
Dieter: 节食者
Entity: 实体
Vary: 变化
Wither: 枯萎；（尤指渐渐）消失
Bellwether: 领头羊；趋势的标志

英语点滴：

最后一句“Which would make certain glaciers, whether or not they wither, better long-term weather bellwethers.”使用了几个押尾韵的单词，“whether，wither，weather，bellwethers”，押韵是口语以及书面语中常用的形式，使语言更加生动。（编辑：胡慧）

（英语原文来自SCIENTIFIC AMERICAN《科学美国人》http://www.sciam.com 作者：Karen Hopkin）

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【听力---SSS---May 5, 2009】

Heather（having flecks of various colors） Today, Gone Tomorrow
A study in the Proceedings of the National Academy of Sciences shows that names that enjoy a meteoric rise in popularity tend to fall just as fast.

Some names never seem to go out of style（过时）, like David or Emily. Some never really catch on（变得流行）. Not many girls are named Laurel, even fewer are named lauryl sulfate. And now a study in the May 5th issue of theProceedings of the National Academy of Sciences shows that the faster a name gains in popularity, the more rapidly it falls.

The authors were interested in why products or cultural phenomena die out. Are they displaced by the Next Big Thing? Or do they fade away（消失，衰弱）, leaving behind a void that has to be filled by something. Well, one cultural taste that’s easy to catalogue is what we name our kids. So the researchers looked at the popularity of baby names in France and the U.S. over the past 100 years. And they found that names that enjoy a meteoric rise—Madison and Brittany come to mind—fall from the charts（流行榜） just as quick.

The scientists also asked expectant（: expecting the birth of a child  *expectant mothers*） couples what names they’d consider inflicting on their children. And found that most parents tend to avoid names they feel are too “faddish,” ones that became overnight sensations, like Kristi and Cody. So those names soon disappear. Which could mean that the world may be safe from Cody Juniors.

有趣的名字现象：流行越快，消失越快
2009-05-12 13:47:29 作者：刘丰祎（译） 来源：新东方
A study in the Proceedings of the National Academy of Sciences shows that names that enjoy a meteoric rise in popularity tend to fall just as fast.
发表在《美国国家科学院院刊》（Proceedings of the National Academy of Sciences）上的一项研究表明，那些快速流行起来的名字一样也很容易被遗忘。

Heather Today, Gone Tomorrow

Some names never seem to go out of style, like David or Emily. Some never really catch on. Not many girls are named Laurel, even fewer are named lauryl sulfate. And now a study in the May 5th issue of the Proceedings of the National Academy of Sciences shows that the faster a name gains in popularity, the more rapidly it falls.

The authors were interested in why products or cultural phenomena die out. Are they displaced by the Next Big Thing? Or do they fade away, leaving behind a void that has to be filled by something. Well, one cultural taste that’s easy to catalogue is what we name our kids. So the researchers looked at the popularity of baby names in France and the U.S. over the past 100 years. And they found that names that enjoy a meteoric rise—Madison and Brittany come to mind—fall from the charts just as quick.

The scientists also asked expectant couples what names they’d consider inflicting on their children. And found that most parents tend to avoid names they feel are too “faddish,” ones that became overnight sensations, like Kristi and Cody. So those names soon disappear. Which could mean that the world may be safe from Cody Juniors.

名字现象：今日鲜花盛开，明天枯萎凋零

有一些名字似乎永远都很时髦，比如David（大卫）或者Emily（埃米莉）。有一些名字就从来没有流行起来过。女孩子名为Laurel（劳雷尔，意思是月桂）的不多见，叫做lauryl sulfate（月桂基硫酸盐）就更少了。目前发表在5月5日的《美国国家科学院院刊》（Proceedings of the National Academy of Sciences）上的一项研究表明，一个名字流行越快，它被遗忘也越快。

该研究的作者们对产品或者文化现象的消亡很感兴趣。它们是被“下一个更好的东西”所替代了呢？还是它们自己逐渐消失了，从而留下了空缺需要其它东西来填补？一种容易归类的文化口味就是我们如何给我们的孩子们取名字。所以，研究者们对法国和美国过去100年内婴儿名字的流行进行了研究。他们发现，那些迅速流行的名字---这让我们想起Madison （麦迪逊）和Brittany（布兰特妮）---也一样迅速地被淡忘。

科学家们也问未来的父母亲，他们会把什么样的名字“强加”给他们的孩子们头上。科学家们发现大多数的父母亲倾向于避免那些他们感到过于“时尚”的名字，这些名字曾经在一夜之间引起轰动，比如Kristi 和 Cody，而这样的名字也很快就消失了。这就意味着这个世界上可能没有人会叫Cody Juniors了。

Vocabulary:

Heather：（植物）石南花；作为形容词等于heathery，表示having flecks of various colors
Meteoric：流星的； 迅速成功的
Popularity：流行
Fade away：逐渐消失
Void：空白；真空
Catalogue：列入目录；记载
Expectant parent：未来的父母
Inflict：使吃苦头
Faddish：时髦的；流行的（编辑：胡慧）

（英语原文来自SCIENTIFIC AMERICAN《科学美国人》http://www.sciam.com 作者：Karen Hopkin）

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【听力---SSS---May 6, 2009】

eBay Lessens Antiquities Looting（抢劫）
A report in Archaeology magazine notes that the ability to easily trade antiquities on eBay has paradoxically lessened looting--because fakes have flooded the market.

When eBay first came onto the scene（出现） more than a decade ago, archaeologists were petrified: easily buying and selling antiquities online might increase the looting and trafficking（贩卖） of archaeological treasures. Now they’re letting out a sigh of relief. Charles Stanish of U.C.L.A. writes in Archaeology magazine that eBay has paradoxically driven down looting.

Stanish is an authority on Andean archaeology. He’s been tracking antiquities on eBay for nine years. He’s also worked with the U.S. customs authority and visited workshops recreating antiquities. Instead of creating an incentive for people to go out and steal artifacts, eBay created a market for fakes, carefully produced by artisans in China, Peru, Mexico and elsewhere. The forgeries can be sold at absurdly low prices.

The flood of fakes has depressed the market, lowering the incentive to loot. And collectors are ever more wary of buying on-line. Stanish estimates that half of the Andean artifacts on eBay10 years ago were fake. Five years later, 95 percent were phony. Bad news for the people who think they’re buying stolen treasures. Good news for archaeologists and the sites they study.

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【听力---SSS---May 7, 2009】

Do Rainforests Create Rain?
In an essay in BioScience magazine, the Wildlife Conservation Society's Douglas Sheil and co-authors discuss the "biotic pump" hypothesis of Russian researchers Anatassia Makarieva and Victor Gorshov, which contends that rainforests attract water vapor, leading to rain, lower local atmospheric pressure and a feedback loop that keeps the whole system going.

Rainforests exist because it rains a lot and that makes the forests grow, right? Well, not so fast（不要（回答得）这么快）. What if it’s not the rain that makes the forests—what if it’s the forests that actually generate the rain? That’s the contention of a paper in BioScience Magazine called How Forests Attract Rain.

The article discusses a mostly overlooked hypothesis that, if right, would explain how big rainforests—like the Amazon—actually drive the entire global water cycle.

Here’s the idea. Forests pull in large amounts of water vapor from surrounding regions and from nearby bodies of water. As the vapor condenses into rain, the local atmospheric pressure drops. Which sucks in more water vapor from outside the forest. Which repeats the process. Creating a positive feedback loop. The whole rainforest-water vapor system is called a biotic pump, because the living forest matter is what’s moving the water.

If proven, the biotic-pump hypothesis could explain how big rainforests far from oceans stay so moist. The info would help climate models. And highlight the potential dangers of deforesting large parts of the pump.

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【听力---SSS---April 1, 2009】

Caffeine Cuts Workout Pain
A study in the International Journal of Sport Nutrition and Exercise Metabolism finds that caffeine cuts the pain of exercise.

Coffee before biking? You may have to stop on the side of the road sooner, but new research suggests that caffeine can help you get more bang from your workout buck, because it keeps you from feeling the burn.

Competitive cyclists and other athletes often consume caffeine before a competition, presumably because they feel like the buzz helps them push a little bit harder. But a study published in the April issue of the International Journal of Sport Nutrition and Exercise Metabolism suggests that the reason caffeine allows athletes to push themselves farther is because it makes exercise hurt that much less.

buzz：（其中一个词条）
a : an excited, euphoric, or stupefied state produced by or as if by a drug b : a state of elation or high spirits

Researchers had 25 subjects engage in two bouts of high intensity cycling. Before each session, they gave every subject a pill. One time, the pill contained the equivalent of two or three cups of coffee. The other time it was just a placebo. The participants all said they felt less pain in their leg muscles during the caffeine-assisted workout than they did with the sugar pill. And it even worked for subjects who already chug（ : to drink a container of (as beer) without pause） a couple thermoses of joe a day. So, the barista can help your biking. Java（: COFFEE） can boost your jogging. And, of course, enjoy those lattes（ : espresso（咖啡） mixed with hot or steamed milk） before your Pilates.

thermos: a container (as a bottle or jar) with a vacuum between an inner and outer wall used to keep material and especially liquids either hot or cold for considerable periods
joe: a beverage made by percolation, infusion, or decoction from the roasted and ground seeds of a coffee plant
barista: a person who makes and serves coffee (as espresso) to the public

Pilates：a system of gentle exercise performed lying down that stretches and lengthens the muscles, designed to improve posture, flexibility, etc

下次，锻炼前请来点儿咖啡
2009-04-02 11:27:31 作者：刘丰祎（译） 来源：新东方
Caffeine Cuts Workout Pain

Coffee before biking? You may have to stop on the side of the road sooner, but new research suggests that caffeine can help you get more bang from your workout buck, because it keeps you from feeling the burn.

Competitive cyclists and other athletes often consume caffeine before a competition, presumably because they feel like the buzz helps them push a little bit harder. But a study published in the April issue of the International Journal of Sport Nutrition and Exercise Medicine suggests that the reason caffeine allows athletes to push themselves farther is because it makes exercise hurt that much less.

Researchers had 25 subjects engage in two bouts of high intensity cycling. Before each session, they gave every subject a pill. One time, the pill contained the equivalent of two or three cups of coffee. The other time it was just a placebo. The participants all said they felt less pain in their leg muscles during the caffeine-assisted workout than they did with the sugar pill. And it even worked for subjects who already chug a couple thermoses of joe a day. So, the barista can help your biking. Java can boost your jogging. And, of course, enjoy those lattes before your Pilates.

咖啡因能减少锻炼中的疼痛

骑自行车锻炼前喝一些咖啡吗？你或许一会儿就要在路边停下来休息，不过新的研究说锻炼前所喝的咖啡“物超所值”，这是因为这些咖啡中的咖啡因让你感受不到肌肉的酸痛感。

竞技类自行车手以及其他运动员经常在比赛前饮用一些咖啡，可能是他们感到咖啡因带来的兴奋能帮助他们在比赛中更加“拼命”。但是发表在4月份的《运动营养以及锻炼医学国际期刊》（International Journal of Sport Nutrition and Exercise Medicine）上的一项研究说，咖啡因能让运动员中更进一步“拼命”的原因在于它使锻炼中的疼痛减少很多。

研究者们让25名实验参与者参加两轮高强度的自行车活动。在每此运动前，他们给这些参与者吃一片药丸。在其中的一次测试中，这种药丸相当于2杯或者3咖啡。另外一次测试中，这种药丸仅仅是安慰剂。与运动前仅仅吃安慰剂相比，实验参与者们都说在有咖啡因帮助的锻炼中，他们感到腿部肌肉的疼痛要轻一些。对于那些已经饮用了几杯热咖啡的参与者来说，这也能起到减轻运动中疼痛的作用。所以，咖啡吧的侍者有助于你的自行车锻炼（注：实际指所喝的咖啡）。咖啡也能有助于你慢跑。当然了，在你参加普拉提健身之前，好好享受你的“拿铁”咖啡吧。

Vocabulary:

Caffeine: 咖啡因
Workout: 锻炼
Bang: 爆炸；砰的声音
Buck: 美元
Burn: （体育锻炼后肌肉的）酸痛感
Competitive: 竞争的
Cyclist: 自行车手
Athlete: 运动员
Consume: 消费
Buzz: 兴奋
Bout: 一场； 一阵
Session: 一节
Equivalent: 等量的
Placebo: 安慰剂
Participant: 参与者
Chug: 一饮而尽
Barista: （送以及调制咖啡的）侍者
Thermos: 暖瓶；复数为thermoses
Joe: （俚语）咖啡
Java：（俚语）咖啡
Boost: 提高；增强
Latte: 热奶沫咖啡(该词来自意大利语)

注释：

1）bang for the buck 也可作 bang for your buck，这个美国习惯用语的意思是“花钱很合算”。比如This restaurant offers people the most bang for the buck. 这个餐馆提供顾客最实惠的服务。

2）Pilates是一种运动健身体系，音译为普拉提。由德裔美国人约瑟夫·普拉提（Joseph Pilates）创立，它的训练目的是通过改变人体肌肉功能从而改善人体脊柱腰椎等的功能。该运动健身法讲究充分应用呼吸和冥想。（编辑：胡慧）

（英语原文来自SCIENTIFIC AMERICAN《科学美国人》http://www.sciam.com 作者：Karen Hopkin）

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至此，从2009-4-1开始的到今天为止的所有SSS都在我的备考日志里有analysis！

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10 Most Fascinating Galaxies of our Universe

Published on 3/10/2009 under Science



The Sombrero Galaxy

The Sombrero Galaxy (also known as M104 or NGC 4594) is an unbarred spiral galaxy in the constellation Virgo. It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its inclined disk. The dark dust lane and the bulge give this galaxy the appearance of a sombrero. The galaxy has an apparent magnitude of +9.0, making it easily visible with amateur telescopes. The large bulge, the central supermassive black hole, and the dust lane all attract the attention of professional astronomers.




Black Eye Galaxy

A spiral galaxy in the Coma Berenices constellation,Messier 64, the famous "Black Eye" galaxy or the "Sleeping Beauty galaxy," has a spectacular dark band of absorbing dust in front of the galaxy's bright nucleus. It is well known among amateur astronomers because of its appearance in small telescopes.





2MASX J00482185-2507365 occulting pair

The 2MASX J00482185-2507365 occulting pair is a pair of overlapping spiral galaxies found in the vicinity of NGC 253, the Sculptor Galaxy. Both galaxies are more distant than NGC 253, with the background galaxy, 2MASX J00482185-2507365, lying at redshift z=0.06, and the foreground galaxy lying between NGC 253 and the background galaxy (0.0008 < z < 0.06). This pair of galaxies illuminates the distribution of galactic dust beyond the visible arms of a spiral galaxy. The heretofore unexpected extent of dust beyond the starry limits of the arms, shows new areas for extragalactic astronomical study. The dusty arms extend 6 times the radii of the starry arms of the galaxy, and is shown silhouetted in HST images against the central and core sections of the background galaxy.




The Whirlpool Galaxy

Also known as Messier 51a, M51a, or NGC 5194, the Whirlpool Galaxy is an interacting grand-design spiral galaxy located at a distance of approximately 23 million light-years in the constellation Canes Venatici. It is one of the most famous spiral galaxies in the sky. The galaxy and its companion (NGC 5195) are easily observed by amateur astronomers, and the two galaxies may even be seen with binoculars. The Whirlpool Galaxy is also a popular target for professional astronomers, who study it to further understanding of galaxy structure (particularly structure associated with the spiral arms) and galaxy interactions.




Grand spiral galaxy

Also known as NGC 123, this fascinating galaxy is dominated by millions of bright stars and dark dust, caught up in a gravitational swirl of spiral arms rotating about the center. Open clusters containing bright blue stars can be seen sprinkled along these spiral arms, while dark lanes of dense interstellar dust can be seen sprinkled between them. Less visible, but detectable, are billions of dim normal stars and vast tracts of interstellar gas, together wielding such high mass that they dominate the dynamics of the inner galaxy. Invisible are even greater amounts of matter in a form we don't yet know - pervasive dark matter needed to explain the motions of the visible in the outer galaxy.




Supernova 1987A

Two decades ago, astronomers spotted one of the brightest exploding stars in more than 400 years: a doomed star, calledSupernova 1987A. This image shows the entire region around the supernova. The most prominent feature in the image is a ring with dozens of bright spots. A shock wave of material unleashed by the stellar blast is slamming into regions along the ring's inner regions, heating them up, and causing them to glow. The ring, about a light-year across, was probably shed by the star about 20,000 years before it exploded. In the next few years, the entire ring will be ablaze as it absorbs the full force of the crash. The glowing ring is expected to become bright enough to illuminate the star's surroundings, providing astronomers with new information on how the star expelled material before the explosion. The image was taken in December 2006 with Hubble's Advanced Camera for Surveys. (Credit: NASA, ESA, and R. Kirshner; Harvard-Smithsonian Center for Astrophysics)




Galaxy NGC 1512

A barred spiral galaxy located some 30 million light years away toward the constellation Horologium, Galaxy NGC 1512 is bright enough to be seen with amateur telescopes. The galaxy is some 70,000 light years across, which is nearly as large as our own Milky Way galaxy. The core of the galaxy is remarkable for its "circumnuclear" starburst ring, which is an amazing circle of young star clusters that spans some 2400 light years across. Galaxy "starbursts" are episodes of vigorous formation of new stars and are found in various galaxy environments.




Galaxy NGC 3370

A dusty spiral galaxy located some 98 million light years away toward the constellation Leo, the center of NGC 3370 shows well delineated dust lanes and an uncommonly ill-defined nucleus. This view of NGC 3370 was obtained by the Hubble Space Telescope using the Advanced Camera for surveys and is sharp enough to identify individual Cepheid variable stars in the galaxy. Cepheid variable stars are used to establish extragalactic distances. In 1994, a Type Ia sypernova exploded in NGC 3370. (Credit: NASA, The Hubble Heritage Team and A. Riess; STScI)




M81

The big and beautiful spiral galaxy M81, in the northern constellation Ursa Major, is one of the brightest galaxies visible in the skies of planet Earth. This superbly detailed view reveals its bright nucleus, grand spiral arms and sweeping cosmic dust lanes with a scale comparable to the Milky Way. Hinting at a disorderly past, a remarkable dust lane runs straight through the disk, below and right of the galactic center, contrary to M81's other prominent spiral features. The errant dust lane may be the lingering result of a close encounter between M81 and its smaller companion galaxy, M82. Scrutiny of variable stars in M81 (aka NGC 3031) has yielded one of the best determined distances for an external galaxy -- 11.8 million light-years.




Hoag's Object

A non-typical galaxy of the type known as a ring galaxy, the appearance of Hoag's Object has interested amateur astronomers as much as its uncommon structure has fascinated professionals. Is this one galaxy or two? This question came to light in 1950 when astronomer Art Hoag chanced upon this unusual extragalactic object. On the outside is a ring dominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older. Between the two is a gap that appears almost completely dark. How Hoag's Object formed remains unknown, although similar objects have now been identified and collectively labeled as a form of ring galaxy. Genesis hypotheses include a galaxy collision billions of years ago and perturbative gravitational interactions involving an unusually shaped core. The above photo taken by the Hubble Space Telescope in July 2001 reveals unprecedented details of Hoag's Object and may yield a better understanding. Hoag's Object spans about 100,000 light years and lies about 600 million light years away toward the constellation of Serpens. Coincidentally, visible in the gap is yet another ring galaxy that likely lies far in the distance.

宇宙中的10大最迷人的星系

摘自《科学》杂志2009年3月10日

宽边帽星系

宽边帽星系（也被称为 “M104”或“NGC4594”）是处女座中的一个涡漩状星系。它有一个明亮的核心，中心有巨大的凸起，外围被一圈厚重的尘埃倾斜地环绕着。外围相对暗淡的一圈尘埃和中心巨大的凸起使这个星系看起来向一个宽边帽。该星系的亮度为+9.0，用小型的天文望远镜就可以看到它。它的巨大凸起，中心的超级黑洞，还有它外围一圈厚重的尘埃，所有这些都深深吸引了众多专业天文学家的目光。



黑眼星系

该星系是一个旋涡状星系，位于后发座，被称为“梅西耶64”、“黑眼”星系、或者“睡美人星系”,在该星系明亮的内核前边是极其壮观而有趣的黑色尘埃云团。对于初级天文爱好者们来说，这是个很有名的星系，用一般的小型天文望远镜就可以看到它。

2MASX J00482185-2507365 重叠星系

2MASX J00482185-2507365 重叠星系由两个螺旋形的星系重叠而成，与玉夫座星系（NGC 253   ）相邻。这两个星系与地球的距离都比玉夫座星系要远，背景星系的红移值为0.06，前景星系则位于玉夫座星系与背景星系之间(红移值介于0.0008到0.06之间)。这两个重叠的星系发出的光照亮了一个螺旋星云的一条可见的旋臂上分布的尘埃。这个在充满恒星的旋臂之外出现的巨大的尘埃云团完全出乎科学家的预料，为银河系外的天文学研究提供的新的课题。尘埃云团构成的旋臂的半径是星系旋臂半径的6倍，并且从HST成像图上的轮廓显示，尘埃旋臂正对着背景星系的的中心。
漩涡状星系

     漩涡状星系又被称为 "梅赛耶51a"，"M51a"或"NGC 5194",与的地球距离为2300万光年，位于北天的猎犬座，是一个庞大的，与它的伴星系共存的螺旋状星系。这是宇宙中的一个非常著名的螺旋状星系。它和它的伴星系（NGC 5195），非常容易被观测到，这两个星系甚至用双筒望远镜都可以看到。这两个星系也是专业天文学家用来研究星系结构（尤其是螺旋状的旋臂）和星系间相互影响的重要研究对象。


大螺旋星系

      

该星系的编号为NGC 123,构成它的上百万颗恒星和尘埃在引力的束缚中形成巨大的，围绕星系中心旋转的螺旋状旋臂。旋臂上点缀着大量的蓝色恒星，恒星带之间是大片的星际尘埃。这个星系不容易被观测到。但是通过特殊装置，还是能观测到数十亿颗昏暗的恒星和大量星际气体，它们的质量很大，是内部星系的原动力。我们只有利用看不见的暗物质理论，才能解释清楚这些可见的外部星系的运动原因。


Supernova 1987A

      

20年前，天文学家们观测到了400多年来亮度最高的超新星爆发的场面：一颗以超新星爆发的形式结束自己生命的恒星，超新星1987A。这张图片显示了这颗超新星周围的整个区域。这张图片中最显著的特点是一个光环和数十个闪亮的光点。这次星际大爆炸所释放出的大量物质被冲击波的力量打的四分五裂，分布在光环内部，他们被爆炸的能量加热，发出灼热的白光。这个光环横跨大约一光年左右的范围，构成光环的物质可能是这颗恒星爆炸的2万年前左右释放出来的。在未来的几年中，因为不断的吸收这次爆炸所释放出的能量，这个光环将变得更加耀眼。它所发出的光芒将照亮这颗恒星周围的大片区域，这将为天文学家们提供有关超新星在爆炸之前如何释放自身物质的更多信息。这张照片是用改进过的哈勃望远镜拍摄于2006年12月。


NGC 1512 星系

NGC 1512 星系是一个位于时钟座星系里的棒旋星系，距离地球大约3000万光年。星系NGC1512非常明亮，人们利用普通望远镜就能看到它。这个星系的直径大约是70000光年，几乎跟我们的银河系的直径一样大。这个星系中心是高度向心的星环，四周是由无数年轻的恒星构成的直径大约是2400光年的星团。恒星爆炸的景象表明该星系里不断有新恒星形成，这种推测在其他几种宇宙环境中已经得到证实。



NGC 3370 星系

星系NGC 3370是一个充满尘埃的螺旋星系，位于狮子座里，距离地球大约9800万光年。星系NGC 3370的中心分布着轮廓鲜明的尘埃带和一个不太容易辨认的核。这张清晰度非常高的图片是哈勃太空望远镜利用高级测量摄像机拍摄，我们通过它甚至能看到该星系里的单个造父变星。造父变星曾被用来测定天文距离。1994年，星系NGC 3370里的一颗Type Ia sypernova发生爆炸。

M81星系

M81位于大熊座星系里，是一个美丽的螺旋星系，也是地球上空肉眼可以看到的最明亮的星系之一。从这张照片上可以清晰看到它的明亮的核子、庞大的螺旋臂和尘埃带，这些尘埃带跟银河里的尘埃带大小差不多。一条明显的尘埃带直接从星盘上穿过，在M81星系中心的下面和右方存在另一个螺旋特征，这说明它曾经历过无序发展时期。而这种不稳定的尘埃带，也可能是由其伴星系M82强力吸引力所致。科学家对M81 的变星进行的探测活动，最终使他们确定了一个银河外星系距地球最准确的距离之一——118亿光年。

哈氏天体

哈氏天体(Hoag's Object)是一个非常著名的环星系。天文爱好者和天文学家对这个星系的独特外貌和与众不同的结构非常感兴趣。这是一个星系还是两个啊? 当1950年天文学家亚特·霍格(Art Hoag)偶然发现这个不寻常的河外星系天体后，这个问题就浮现在大家眼前。它外围是由明亮的蓝色恒星组成的环状物，而中心处的圆球则主要是由许多可能较老的红色恒星构成。介于两者之间的是一道几乎完全黑暗的裂缝。虽然这些类似的天体已被识别出，并被归类为环状星系，但是哈氏天体(Hoag's Object)是如何形成的，目前仍不为人知。此种星系的起源假说包括：在数十亿年前所发生的星系碰撞，或者是一个具有不寻常形状的星系核在紊乱重力作用下产生的。上图的照片是哈伯太空望远镜在2001年7月拍摄的，它显示出哈氏天体前所未有的细节，这或许有助于天文学家更好地了解此类星系。哈氏天体跨越大约10万光年，位于北天的巨蛇座星系内，距离地球大约6亿光年。凑巧的是，从这条缝隙里看过去，还能看见另一个更加遥远的环星系。

liunian1031UID：2670872

天……你的备考日志简直像百科全书一样……
26号一战不知能否成功，如果当初就如LZ一样奋斗着，估计也就不会这么心虚了……

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Active Galaxies and Quasars
Active galaxies are galaxies which have a small core of emission embedded in an otherwise typical galaxy. This core may be highly variable and very bright compared to the rest of the galaxy. Models of active galaxies concentrate on the possibility of a supermassive black hole which lies at the center of the galaxy. The dense central galaxy provides material which accretes（这些material被增加到black hole里：To grow or increase gradually, as by addition.） onto the black hole releasing a large amount of gravitational energy. Part of the energy in this hot plasma is emitted as x-rays and gamma rays.

For "normal" galaxies, we can think of the total energy they emit as the sum of the emission from each of the stars found in the galaxy. For the "active" galaxies, this is not true. There is a great deal more emitted energy than there should be... and this excess energy is found in the infrared, radio, UV, and X-ray regions of the electromagnetic spectrum. The energy emitted by an active galaxy (or AGN) is anything but "normal". So what is happening in these galaxies to produce such an energetic output?

There are several types of active galaxies: Seyferts, quasars, and blazars. Most scientists believe that, even though these types look very different to us, they are really all the same thing viewed from different directions! Quasars are active galaxies which are all very, very, very far away from us. Some of the quasars we have seen so far are 12 billion light-years away! Blazars are very bright in the radio band, which results from looking directly down a jet which is emitting in synchrotron radiation. On the other hand, if the jet is not pointing toward you at all, and the dusty disk of material which lies in the plane of the galaxy is in the way, you would see just what we see from the Seyferts. By measuring their redshifts, we find that Seyferts are much closer to us than quasars or blazars.

redshift：红移
天体的光或者其他电磁辐射可能由于三种效应被拉伸而使波长变长。因为红光的波长比蓝光的长，所以这种拉伸对光学波段光谱特征的影响是将它们移向光谱的红端，于是全部三种过程都被称为‘红移’。
In physics and astronomy, redshift occurs when electromagnetic radiation—usually visible light—emitted or reflected by an object is shifted towards the (less energetic) red end of the electromagnetic spectrum due to the Doppler effect or other gravitationally-induced effects. More generally, redshift is defined as an increase in the wavelength of electromagnetic radiation received by a detector compared with the wavelength emitted by the source. This increase in wavelength corresponds to a drop in the frequency of the electromagnetic radiation. Conversely, a decrease in wavelength is called blue shift.

Active galaxies are intensely studied at all wavelengths. Since they can change their behavior on short timescales, it is useful to study them simultaneously at all energies. X-ray and gamma-ray observations have proven to be important parts of this multiwavelength approach since many high-energy quasars emit a large fraction of their power at such energies. X-rays can penetrate outward from very near the center of a galaxy. Since that is where the "engines" of AGN are located, X-rays provide scientists with unique insights into the physical processes occurring there. In addition, gamma-ray observations alone can provide valuable information on the nature of particle acceleration in the quasar jet, and clues as to how the particles interact with their surroundings.
                                                                                      

                                                                        A diagram of an active galaxy, showing the primary components.


Seyfert Galaxies
Of the two types of Active Galactic Nuclei (AGN) which emit gamma rays, Seyfert galaxies are the low-energy gamma-ray sources.Seyfert galaxies typically emit most of their gamma rays up to energies of about 100 keV and then fade as we observe them at higher energies. Early gamma-ray observations of Seyfert galaxies indicated that photons were detected up to MeV energies, but more sensitive observations have cast doubt on this possibility. At these low gamma-ray energies, the emission is usually a smooth continuation of the X-ray emission from such objects. This generally indicates that the physical processes creating the gamma rays are thermal processes similar to those responsible for emission from galactic black hole sources. As a result, gamma-ray studies of the high-energy spectrum and variability can give scientists important information about the physical environment in the AGN.

Observations of Seyfert galaxies in gamma rays are also important for studies of the cosmic gamma-ray background. Even in regions of the sky where there are no point sources, a faint gamma-ray glow is detectable. It may be that this glow is the sum of many faint galaxies or perhaps a more exotic process. Studies of individual Seyfert galaxies can be combined with a model of how such objects are distributed in the Universe to compare to the diffuse gamma-ray background. In this way, astronomers not only learn about the interesting AGN phenomena, but learn more about the general nature of the Universe as a whole .
                                                                                       

                                                                                      An artists concept of an active galactic nuclei



Quasars
One of the most remarkable trends in gamma-ray astronomy in recent years has been the emergence of high-energy gamma-ray quasars as an important component of the gamma-ray sky. At gamma-ray energies, these active galaxies are bright; they are highly variable at all energies. Unlike the Seyfert type AGN, most of these sources are preferentially detected at high energies, usually 100 MeV or more. In fact, they have been detected above 1 GeV, and some up to several TeV! Given the large distances to these objects and the strong emission of high-energy gamma rays, these are the most powerful particle accelerators in the Universe. Over 50 high-energy quasars are known at this time. Some appear as fuzzy stars that can be seen with large amateur telescopes.Many astronomers believe that Seyfert galaxies and high-energy quasars are basically the same type of objects, but we are simply viewing them differently. Radio observations of AGN often show powerful jets, streams of particles coming from the central source -- like water from a spigot. Charged particles are accelerated to nearly the speed of light in these jets. In the unified view of active galaxies, high-energy quasars are being viewed with the jet pointed towards us which allows us to see the resulting energetic radiation. With Seyfert galaxies, we are viewing from the side and do not see the very high-energy radiation which is traveling down the jet.
                                                                          
         

The region of the sky containing one of the high-energy quasars, PKS 0528+134, is shown at two different times using the EGRET instrument on the
Compton Gamma-Ray Observatory. These active galaxies are highly variable, strongly emitting gamma-rays sometimes, disappearing at other times.

Blazars
The AGNs observed at higher energies form a subclass of AGNs known as blazars; a blazar is believed to be an AGN which has one of its relativistic jets pointed toward the Earth so that what we observe is primarily emission from the jet region. They are thus similar to quasars, but are not observed to be as luminous. The visible and gamma-ray emission from blazars is variable on timescales from minutes to days. Although theories exist as to the causes of this variability, the sparse data do not yet allow any of the ideas to be tested.

To date more than 60 blazars have been detected by the EGRET experiment aboard the Compton Gamma-Ray Observatory. All these objects appear to emit most of their bolometric luminosity at gamma-ray energies and, in addition, are strong extragalactic radio sources.

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How the Milky Way Works
by Craig Freudenrich, Ph.D.
A look at the night sky at any time of year will reveal a faint band of light stretching across the sky, either through the middle or near the horizon. The ancient Greeks saw this band o f light and called it "galaxies kuklos," for "milk circle." The Romans called it the "Milky Way." In 1610, Galileo used the first telescopesand determined that the light of the Milky Way comes from billions of dim stars that surround us.

Milky Way Image Gallery

Tony Hallas/Science Fiction/Getty Images
The Milky Way, from the bright star Sirius in the upper right corner all the way down to Eta Carina, the red nebula visible on the horizon, as seen from the Florida Keys. See more
Milky Way pictures.

For centuries, astronomers asked many basic questions about the Milky Way. What is it? What is it made of? What is it shaped like? These questions were difficult to answer for several reasons.

• We live inside the Milky Way. It's like living inside a gigantic box and asking, what is the box shaped like? What is it made of? How do you know?
• Early astronomers were limited by technology. The early telescopes weren't very large, didn't have much range and couldn't magnify great distances or resolve them.
• Early telescopes could detect only visible light. The Milky Way contains a lot of dust that obstructed their views. In some directions, looking at the Milky Way is like looking through a dust storm.

The 20th century brought great advancements in telescope technology. Large optical, radio, infrared, and X-ray telescopes (both ground-based and orbiting space telescopes) allowed astronomers to peer through the vast quantities of dust and far into space. With these tools, they could piece together what the Milky Way actually looks like.
What they discovered was amazing:

• The Milky Way is actually a galaxy -- a large system of stars, gas (mostly hydrogen), dust and dark matter that orbits a common center and is bound together by gravity.
• Our galaxy is spiral-shaped.
• Contrary to popular belief, our solar system is not at the center of the galaxy.
• The Milky Way is but one of billions of galaxies in the universe.

Come follow us on a journey of discovery as we explore the Milky Way. We'll examine how astronomers figured out its shape, size and structure. We'll look at how the stars within it move and how the Milky Way compares to other galaxies.

Early Milky Way Theories

As we mentioned, Galileo discovered that the Milky Way is made of dim stars, but what about its shape? How can you tell the shape of something if you're inside it? In the late 1700s, astronomer Sir William Herschel addressed this question. Herschel reasoned that if the Milky Way was a sphere, we should see numerous stars in all directions. So, he and his sister Caroline counted the stars in more than 600 areas of the sky. They found that there were more stars in the directions of the band of the Milky Way than above and below. Herschel concluded that the Milky Way was a disk-shaped structure. And because he found about the same numbers of stars in all directions along the disk, he concluded that the sun was near the center of the disk.
Around 1920, a Dutch astronomer named Jacobus Kapetyn measured the apparent distances to nearby and remote stars using the technique of parallax. Because parallax involved measuring the motions of stars, he compared the motions of distant stars with nearby ones. He concluded that the Milky Way was a disc approximately 20 kiloparsecs, or 65,000 light years, in diameter (one kiloparsec = 3,260 light years). Kapetyn also concluded that the sun was at or near the center of the Milky Way.
But future astronomers would question these ideas, and advanced technology would help them dispute the theories and come up with more accurate measurements.

Measuring Distances to the Stars If you hold your thumb out at arm's length and then alternately open and close each eye while looking at it, you will see that your thumb apparently moves or shifts against the background. This shift is called a parallax shift. As you move your thumb in closer to your nose and repeat the process, you should notice that the shift gets bigger. Astronomers can use this same technique to measure distances to the stars. As the Earth orbits the sun, a given star's position changes against the background of other stars. By comparing photographs of the star at six-month intervals, astronomers can measure the degree of the shift and obtain the angle of parallax (half the parallax shift = theta or Θ). By knowing the angle of parallax and the radius of the Earth’s orbit (R), astronomers can calculate the distance to the star (D) using trigonometry: D = R x cotangent (theta) or D = RCotΘ. Parallax measurements are reliable for stars with distances less than or equal to 50 parsecs. For distances greater than this, astronomers must find variable star markers and use the luminosity-distance relationships (see next page).

Globular Clusters and Spiral Nebulae

Around the time that Kapetyn published his model of the Milky Way, his colleague Harlow Shapely noticed that a type of star cluster called a globular cluster had a unique distribution in the sky. Although few globular clusters were found within the Milky Way band, there were a lot of them above and below it. Shapely decided to map the distribution of globular clusters and measure their distances using variable star markers within the clusters and the luminosity-distance relationship (see sidebar). Shapely found that globular clusters were found in a spherical distribution and concentrated near the constellation of Sagittarius. Shapely concluded that the center of the galaxy was near Sagittarius, not the sun, and that the Milky Way was about 100 kiloparsecs in diameter.
Shapely was involved in a great debate about the nature of spiral nebulae (faint patches of light visible in the night sky). He believed that they were "island universes," or galaxies outside the Milky Way. Another astronomer, Heber Curtis, believed that spiral nebulae were part of the Milky Way. Edwin Hubble's observations of Cepheid variables finally settled the debate -- the nebulae were indeed outside the Milky Way.
But questions still remained. What shape was the Milky Way, and what exactly existed inside it?

Luminosity-Distance Relationship Professional and amateur astronomers alike can measure a star's brightness by putting a photometer or charge-coupled device on the end of a telescope. If they know the star's brightness and the distance to the star, they can calculate the amount of energy that the star puts out, or its luminosity (luminosity = brightness x 12.57 x (distance)2). Conversely, if you know a star’s luminosity, you can calculate its distance from the Earth. Certain stars -- such as RR Lyrae and Cepheid variables -- can serve as light standards. These stars change their brightness regularly and the luminosity is directly related to the period of their brightness cycle.To determine the luminosities of the globular clusters, Shapely measured the periods of brightness of the RR Lyrae stars in the clusters. Once he knew the luminosities, he could calculate their distances from Earth. See How Galaxies Work for how astronomer Edwin Hubble used a similar technique with Cepheid variable stars to determine that spiral nebulae were farther than the limits of the Milky Way.

What shape is the Milky Way?

Edwin Hubble studied galaxies and classified them into various types of elliptical and spiral galaxies. The spiral galaxies were characterized by disk shapes with spiral arms. It stood to reason that because the Milky Way was disk-shaped and because spiral galaxies were disk-shaped, the Milky Way was probably a spiral galaxy.

Image courtesy
NASA

In the 1930s, astronomer R. J. Trumpler realized that the estimates of the size of the Milky Way galaxy by Kapetyn and others were off because the measurements had relied on observations in the visible wavelengths. Trumpler concluded that the vast amounts of dust in the plane of the Milky Way absorbed light in the visible wavelengths and caused faraway stars and clusters to appear dimmer than they actually were. Therefore, to accurately map stars and star clusters within the disk of the Milky Way, astronomers would need a way to peer through the dust.

The Doppler Effect Much like the high-pitched sound from a fire-truck siren gets lower as the truck moves away, the movement of stars affects the wavelengths of light that we receive from them. This phenomenon is called the Doppler effect. We can measure the Doppler effect by measuring lines in a star's spectrum and comparing them to the spectrum of a standard lamp. The amount of the Doppler shift tells us how fast the star is moving relative to us. In addition, the direction of the Doppler shift can tell us the direction of the star's movement. If the spectrum of a star is shifted to the blue end, the star is moving toward us; if the spectrum is shifted to the red end, the star is moving away from us.

In the 1950s, the first radio telescopeswere invented. Astronomers discovered that hydrogen atoms emitted radiation in the radio wavelengths and that these radio waves could penetrate the dust in the Milky Way. So, it became possible to map the spiral arms of the Milky Way. The key was marker stars like those used in distance measurements. Astronomers found that class O and B stars would work. These stars had several features:

• Brightness:
  They're highly visible and are often found in small groups or associations.
• Heat:
  They emit multiple wavelengths (visible, infrared, radio).
• Short life:
  They live for about 100 million years, so, considering the rate at which stars orbit the galaxy's center, they don't move far from where they were born.

Astronomers could use radio telescopes to accurately map the positions of these O and B stars and use the Doppler shifts of the radio spectrum to determine their rates of motion. When they did this with many stars, they were able to produce combined radio and optical maps of the Milky Way's spiral arms. Each arm is named for the constellations that exist within it.
Astronomers think that the motion of the material around the galactic center sets up density waves(areas of high and low density), much like you see when you stir cake batter with an electric mixer. These density waves are thought to cause the spiral nature of the galaxy.
So, by examining the sky in multiple wavelengths (radio, infrared, visible, ultraviolet, X-ray) with various ground-based and space-based telescopes, we can get different views of the Milky Way.
On the next page we'll look into exactly what's inside the Milky Way.

Milky Way Structure

According to Edwin Hubble's classification system, the Milky Way is a spiral galaxy, although more recent mapping evidence indicates that it may be a barred spiral galaxy. The Milky Way has more than 200 billion stars (this was estimated from its mass -- see next page). It's approximately 100,000 light years in diameter, and the sun is located about 28,000 light years from the center. If we look at the structure of the Milky Way as it would appear from the outside, we can see the following parts:

• Galactic disk:
  This is where most of the Milky Way's stars are located. The disk is made of old and young stars, as well as vast amounts of gas and dust. Stars within the disk orbit the galactic center in roughly circular orbits. (Gravitational interactions between the stars cause the circular motions to have some up-and-down motion, like horses on a merry-go-round). The disk itself is broken up into these parts:
  Nucleus:
  The center of the disk
  Bulge:
  This is the area around the nucleus, including the immediate areas above and below the plane of the disk.
  Spiral arms:
  These areas extend outward from the center. Our solar system is located in one of the spiral arms of the Milky Way.
• Globular clusters:
  A few hundred of these are scattered above and below the plane of the disk. Globular clusters orbit the galactic center in elliptical orbits in which the directions are randomly scattered. The stars in the globular clusters are much older stars than those in the galactic disk, and there's little or no gas and dust.
• Halo:
  This is a large, dim, region that surrounds the entire galaxy. The halo is made of hot gas and possibly dark matter.

All of these components orbit the nucleus and are held together by gravity. Because gravity depends upon mass, you might think that most of a galaxy's mass would lie in the galactic disk or near the center of the disk. However, by studying the rotation curves of the Milky Way and other galaxies, astronomers have concluded that most of the mass lies in the outer portions of the galaxy (like the halo), where there is little light given off from stars or gases.
The Milky Way's gravity acts on two smaller satellite galaxies called the Large and Small Magellanic Clouds (named after Ferdinand Magellan, the Portuguese explorer). They orbit below the plane of the Milky Way and are visible in the Southern Hemisphere. The Large Magellanic Cloud is about 70,000 light years in diameter and 160,000 light years away from the Milky Way. Astronomers think that the Milky Way is actually siphoning off gas and dust from these satellite galaxies as they orbit.
So, how many stars does the Milky Way actually contain? We'll show you the formula on the next page.

How many stars are in the Milky Way?

We mentioned earlier that astronomers have estimated the number of stars in the Milky Way from measurements of the galaxy's mass. But how do you measure the mass of a galaxy? You obviously can't put it on a scale. Instead, you use its orbital motion. From Newton's version of Kepler's Third Law of Planetary Motion, the orbital speed of an object in circular orbit, and a little algebra, you can derive an equation to calculate the amount of mass (M[size=-2]r) that lies within any circular orbit with a radius (r).

E.L. Wright (UCLA), The COBE Project, DIRBE,
NASA
It's complicated, but you can use Newton's version of Kepler's Third Law to figure out how many stars are in the Milky Way.

When we add the portion of the Milky Way that lies outside the sun’s orbit, we get approximately 200 billion stars.

thatllUID：2538832

【听力---SSS---September 21, 2009】

Torture Interferes with Memory
In the journal Trends in Cognitive Sciences, psychologist Share O'Mara notes that torture can interfere with the brain's memory retrieval apparatus, making it counterproductive to the aim of producing useful information.

apparatus：
1 a : a set of materials or equipment designed for a particular use b : a group of anatomical or cytological parts functioning together *mitotic apparatus* c : an instrument or appliance designed for a specific operation
2 : the functional processes by means of which a systematized activity is carried out *the apparatus of society*: as a : the machinery of government b : the organization of a political party or an underground movement

You’ve heard of waterboarding（水刑） used as a means to get suspected terrorists to talk. Some people object to such methods on the grounds that they amount to torture. But in the journal Trends in Cognitive Sciences, psychologist Shane O’Mara of Trinity College in Dublin raises another objection: torture's not likely to work.

Proponents claim that waterboarding's effective because prisoners will tell the truth to make the interrogation stop. But O’Mara says that’s not supported by scientific evidence. Harsh interrogation doesn’t motivate prisoners to tell the truth. It motivates them to talk. Because while they’re talking they’re not being waterboarded. But that doesn’t mean that what they say is true.

What’s more, prolonged extreme stress impairs memory retrieval. American Special Ops soldiers have been shown to have trouble recalling things they’d learned before being subjected to food- or sleep-deprivation as part of their training. That’s because stress hormones can compromise brain activity, especially in regions involved in memory.

O’Mara notes that mildly stressful events actually facilitate recall. So simply capturing, moving and then questioning prisoners, he says, should be stressful enough to get the information flowing.

thatllUID：2538832

April 10th, 2008
Why Pluto is No Longer a Planet

Written by Fraser Cain


This has got to be be one of the most heartbreaking questions I get asked, "Why Isn't Pluto a Planet". And I get it a lot. I was expecting that a few years after the International Astronomical Union's controversial decision, the debate would have settled down and people would finally accept it. But no, it's still a sore point for many people – Pluto is not a planet (let that sink in). In this article, I'll explain the events that led up to the decision, the current state of planetary definition, and any hope Pluto has for the future. Let's find out why Pluto is no longer considered a planet.

Pluto was first discovered in 1930 by Clyde W. Tombaugh at the Lowell Observatory in Flagstaff Arizona. Astronomers had long predicted that there would be a ninth planet in the Solar System, which they called Planet X. Only 22 at the time, Tombaugh was given the laborious task of comparing photographic plates. These were two images of a region of the sky, taken two weeks apart. Any moving object, like an asteroid, comet or planet, would appear to jump from one photograph to the next.

After a year of observations, Tombaugh finally discovered an object in the right orbit, and declared that he had discovered Planet X. Because they had discovered it, the Lowell team were allowed to name it. They settled on Pluto, a name suggested by an 11-year old school girl in Oxford, England (no, it wasn't named after the Disney character, but the Roman god of the underworld).

The Solar System now had 9 planets. Astronomers weren't sure about Pluto's mass until the discovery of its largest Moon, Charon, in 1978. And by knowing its mass (0.0021 Earths), they could more accurately gauge its size. The most accurate measurement currently gives the size of Pluto at 2,400 km (1,500 miles) across. Although this is small, Mercury is only 4,880 km (3,032 miles) across. Pluto is tiny, but it was considered larger than anything else past the orbit of Neptune.

Over the last few decades, powerful new ground and space-based observatories have completely changed previous understanding of the outer Solar System. Instead of being the only planet in its region, like the rest of the Solar System, Pluto and its moons are now known to be just a large example of a collection of objects called the Kuiper Belt. This region extends from the orbit of Neptune out to 55 astronomical units (55 times the distance of the Earth to the Sun).

Astronomers estimate that there are at least 70,000 icy objects, with the same composition as Pluto, that measure 100 km across or more in the Kuiper Belt. And according to the new rules, Pluto is not a planet. It's just another Kuiper Belt object.

Here's the problem. Astronomers had been turning up larger and larger objects in the Kuiper Belt. 2005 FY9, discovered by Caltech astronomer Mike Brown and his team is only a little smaller than Pluto. And there are several other Kuiper Belt objects in that same classification.
Astronomers realized that it was only a matter of time before an object larger than Pluto was discovered in the Kuiper Belt.

And in 2005, Mike Brown and his team dropped the bombshell. They had discovered an object, further out than the orbit of Pluto that was probably the same size, or even larger. Officially named 2003 UB313, the object was later designated as Eris. Since its discovery, astronomers have determined that Pluto's size is approximately 2,600 km (1,600 miles) across. It also has approximately 25% more mass than Pluto.

With Eris being larger, made of the same ice/rock mixture, and more massive than Pluto, the concept that we have nine planets in the Solar System began to fall apart. What is Eris, planet or Kuiper Belt Object; what is Pluto, for that matter? Astronomers decided they would make a final decision about the definition of a planet at the XXVIth General Assembly of the International Astronomical Union, which was held from August 14 to August 25, 2006 in Prague, Czech Republic.

Astronomers from the association were given the opportunity to vote on the definition ofplanets. One version of the definition would have actually boosted the number of planets to 12; Pluto was still a planet, and so were Eris and even Ceres, which had been thought of as the largest asteroid. A different proposal kept the total at 9, defining the planets as just the familiar ones we know without any scientific rationale, and a third would drop the number of planets down to 8, and Pluto would be out of the planet club. But, then… what is Pluto?
In the end, astronomers voted for the controversial decision of demoting Pluto (and Eris) down to the newly created classification of "dwarf planet".

Is Pluto a planet? Does it qualify? For an object to be a planet, it needs to meet these three requirements defined by the IAU:

• It needs to be in orbit around the Sun– Yes, so maybe Pluto is a planet.
• It needs to have enough gravity to pull itself into a spherical shape – Pluto…check
• It needs to have "cleared the neighborhood" of its orbit – Uh oh. Here's the rule breaker. According to this, Pluto is not a planet.

What does "cleared its neighborhood" mean? As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects, they either consume them, or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.

Any object that doesn't meet this 3rd criteria is considered a dwarf planet. And so, Pluto is a dwarf planet. There are still many objects with similar size and mass to Pluto jostling around in its orbit. And until Pluto crashes into many of them and gains mass, it will remain a dwarf planet. Eris suffers from the same problem.

It's not impossible to imagine a future, though, where astronomers discover a large enough object in the distant Solar System that could qualify for planethood status. Then our Solar System would have 9 planets again.

Even though Pluto is a dwarf planet, and no longer officially a planet, it'll still be a fascinating target for study. And that's why NASA has sent their New Horizons spacecraft off to visit it. New Horizons will reach Pluto in July 2015, and capture the first close-up images of the (dwarf) planet's surface.

Space enthusiasts will marvel at the beauty and remoteness of Pluto, and the painful deplaneting memories will fade. We'll just be able to appreciate it as Pluto, and not worry how to categorize it. At least now you know why Pluto was demoted.

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Here's a new portrait of the Solar System, with tiny Pluto and the other dwarf planets. You can see how they compare in size to the rest of the planets.