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
Mounting evidence has led astronomers to just such an improbable conclusion, at least 90 percent and possibly 99 percent of all
Mounting evidence has led astronomers to just such an improbable conclusion, at least 90 percent and possibly 99 percent of all
admin
2013-05-04
71
问题
Mounting evidence has led astronomers to just such an improbable conclusion, at least 90 percent and possibly 99 percent of all matter in the universe is completely invisible. Astronomers call this invisible stuff dark matter.
An astronomer first reported the invisible matter after noting some unusual behavior in visible matter. In 1993, Swiss astrophysicist Fritz Zwicky observed that galaxies in a cluster of galaxies travelled at higher speeds than expected. He concluded that something was causing strange gravitational effects on these galaxies.
Galaxies are like vast islands in deep space containing billions of stars that are held together by the force of gravity. Some galaxies are part of larger systems called clusters, which contain many galaxies. Most galaxies, however, belong to smaller systems called groups. Groups and clusters in turn form even larger structures known as superclusters. Just as the force of gravity keeps stars together in galaxies, so the force of gravity appears to keep galaxies together in clusters.
This same force of gravity keeps planets orbiting around the sun, rather than flying off into space. How great a force gravity exerts depends on the mass of the objects attracted and the distance between them, a principle discovered by Newton. The amount of mass and the distance between objects also determine how fast the objects travel as they orbit each other. For example, in our solar system, the sun is the most massive object, making up about 99.9 percent of the mass of the solar system, and the force of its gravity keeps Earth and the other planets in orbit around it. The orbital speeds of the planets decline with increasing distance from the sun. The planet nearest to the sun, Mercury, travels at an orbital speed of 48 kilometers per second, while the distant planet Pluto orbits at speed of 4.7 kilometers per second.
In astronomical terms, a cluster ______.
选项
A、consists of galaxies
B、makes up superclusters
C、consists of groups
D、makes up a group
答案
A
解析
第三段对几个概念进行了说明:星系(galaxy)由星星组成,几个星系组成一个星团 (cluster),规模小的几个星系组成星群(group),而星团、星群又组成更大的超星系团。星群与星团不是个体与整体的关系,二者的区别仅在于其大小而已。
转载请注明原文地址:https://kaotiyun.com/show/7GB7777K
0
大学英语六级
相关试题推荐
Everdippedintothebiscuittinthendecidedyou’veruinedyourdietsoyoumayaswelleatthelot?Orthoughtthatbecauseyo
Everdippedintothebiscuittinthendecidedyou’veruinedyourdietsoyoumayaswelleatthelot?Orthoughtthatbecauseyo
Ifyouareanythinglikeme,youleftthetheaterafterSexandtheCity2andthought,thereoughttobealawagainstalooks-
Ifyouareanythinglikeme,youleftthetheaterafterSexandtheCity2andthought,thereoughttobealawagainstalooks-
Thefatherthoughttheevent______(可以提醒儿子对生活不可太消极).
TheconclusionofanewstudybysociologistsfromtheUniversityofTorontowon’tcomeasasurprisetoworkingwomen:theyfee
TheconclusionofanewstudybysociologistsfromtheUniversityofTorontowon’tcomeasasurprisetoworkingwomen:theyfee
TheconclusionofanewstudybysociologistsfromtheUniversityofTorontowon’tcomeasasurprisetoworkingwomen:theyfee
随机试题
我国根据病原微生物的传染性、感染后对个体或群体的危害程度,将病原微生物分为()。[2010年真题]
家畜机体内最粗最长的神经是
物质上和形态上的城市化具体反映有()。
背景资料某钢厂将一条年产100万t宽厚板轧制生产线的建设项目,通过招标确定该工程中的板坯加热炉车间和热轧制车间由具有冶金施工总承包一级资质的企业实施总承包,负责土建施工,厂房钢结构制作、安装,车间内300t桥式起重机的安装,设备安装与调试,三电工程的施工
E-mail地址ZZZ@yahoo.com.cn中,()表示用户名。
一般资料:求助者,女性,28岁,已婚,本科学历,教师。案例介绍:求助者是独生女,家境富足。当年谈恋爱时,其父母曾明确要求她婚后要与他们共同居住,孩子随娘家姓,求助者的男友没有明确提出反对意见。求助者结婚后与父母同住,一个多月前求助者顺产一个男婴,
反映古希腊著名哲学家柏拉图的教育思想的代表作品是()。
游记文学在现代已成为相对_______的散文品种之一,现代文学创作中游记文学获得了空前的成就,不但出现了郁达夫、朱自清这样描山绘水、记录社会风俗的圣手,也出现了一批_______、永留史册的名篇。填入划横线部分最恰当的一项是:
下面是关于PC机中USB和IEEE-1394的叙述,其中正确的是______。
Researchersusedtobelievethatasenseofrealcaringaboutotherscameaspeoplegrowintoadulthood.Butnowstudiesarefin
最新回复
(
0
)