首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Galaxies are the major’ building blocks Of the universe: A galaxy is giant family of many millions of stars, and it is held to
Galaxies are the major’ building blocks Of the universe: A galaxy is giant family of many millions of stars, and it is held to
admin
2009-03-16
28
问题
Galaxies are the major’ building blocks Of the universe: A galaxy is giant family of many millions of stars, and it is held together by its own gravitational field. Most of the material universe is organized into galaxies of stars together with gas and dust.
There are three main types of galaxy: spiral, elliptical, and irregular. The Milky Way is a spiral galaxy, a flattish disc of stars with two spiral arms emerging from its central nucleus. About one-quarter of all galaxies have this shape. Spiral galaxies are well supplied with the interstellar gas in which new stars form: as the rotating spiral pattern sweeps around the galaxy it compresses gas and dust, triggering the formation of bright young stars. The elliptical galaxies have a symmetrical elliptical or spheroidal shape with no obvious structure. Most of their member stars are very old and since ellipticals are devoid of interstellar gas, no new stars are forming in them. The biggest and brightest galaxies in the universe are ellipticals with masses of about 1013 times that of the sun, these giants may frequently be sources of strong radio emission, in which case they are called radio galaxies. About two-thirds of all galaxies are elliptical. Irregular galaxies comprise about one-tenth of all galaxies and they come in many subclasses.
Measurement in space is quite different from measurement on Earth. Some terrestrial distances can be expressed as intervals of time, the time to fly from one continent to another or the time it takes to drive to work, for example. By comparison with these familiar yardsticks, the distances to the galaxies are incomprehensibly large, but they too are made more manageable by using a time calibration, in this case the distance that light travels in one year. On such a scale the nearest giant spiral galaxy, the Andromeda galaxy, is two million light years away. The most distant luminous objects seen by telescopes are probably ten thousand million light years away. Their light was already halfway here before the Earth even formed. The light from the nearby Virgo galaxy set out when reptiles still dominated the animal world.
选项
A、The Milky Way.
B、Major categories of galaxies.
C、How elliptical galaxies are formed.
D、Differences between irregular and spiral galaxies.
答案
B
解析
转载请注明原文地址:https://kaotiyun.com/show/NDPd777K
本试题收录于:
公共英语四级笔试题库公共英语(PETS)分类
0
公共英语四级笔试
公共英语(PETS)
相关试题推荐
"TheissueofonlineprivacyintheInteractagefoundnewurgencyfollowingtheSept.11terroristattacks,sparkingdebateove
RecentsurveysshowthatJapaneseyouthhavebecomea"MeGeneration"thatrejectstraditionalvalues."Around1980manyJap
RecentsurveysshowthatJapaneseyouthhavebecomea"MeGeneration"thatrejectstraditionalvalues."Around1980manyJap
RecentsurveysshowthatJapaneseyouthhavebecomea"MeGeneration"thatrejectstraditionalvalues."Around1980manyJap
Accordingtothewoman,whywomenaremuchbetteratdealingwithmorethanonethingatatime?
What’stheaverageincreaseperyearofforeignstudentpopulationintheperiodbetween1985and1990intermsofpercentage?
In1959theaverageAmericanfamilypaid$989forayear’ssupplyoffood.In1972thefamilypaid$1,311.Thatwasaprice
In1959theaverageAmericanfamilypaid$989forayear’ssupplyoffood.In1972thefamilypaid$1,311.Thatwasaprice
What’stheaverageincreaseperyearofforeignstudentpopulationintheperiodbetween1985and1990intermsofpercentage?
随机试题
信息系统中,分散的用户不但可以共享包括数据在内的各种计算机资源,而且还可以在系统的支持下,合作完成某一工作,例如共同拟订计划、共同设计产品等。这已成为信息系统发展的一个趋势,称为_______。
一般保证,是指当事人在保证合同中约定,在债务人不能履行债务时,由保证人承担保证责任的保证。在一般保证中,保证人享有()。
转移性低钠血症时,实验室检查可见
根据《处方管理办法》规定,麻醉药品处方印制用纸应为
某女,32岁,结婚5年未孕,月经一直不规律,医生考虑为无排卵性功血。根据患者的月经史,采取下列哪一种方法可达到治疗目的()
椰枣干
导游既代表接待方旅行社的利益,又肩负着维护游客合法权益的责任,这体现的是导游服务纽带作用中的()方面。
我国国家行政机关实行()。
[*]
下列反常积分中收敛的是
最新回复
(
0
)