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
The explosion of a star is an awesome event. The most violent of these cataclysms, which produce supernovae, probably destroys a
The explosion of a star is an awesome event. The most violent of these cataclysms, which produce supernovae, probably destroys a
admin
2013-01-15
61
问题
The explosion of a star is an awesome event. The most violent of these cataclysms, which produce supernovae, probably destroys a star completely. Within our galaxy of roughly 100 billion stars the last supernova was observed in 1604. Much smaller explosions, however, occur quite frequently, giving rise to what astronomers call novae and dwarf novae. On the order of 25 novae occur in our galaxy every year, but only two or three are near enough to be observed. About 100 dwarf novae are known altogether. If the exploding star is in a nearby part of the galaxy, it may create a "new star" that was not previously visible to the naked eye. The last new star of this sort that could be observed clearly from the Northern Hemisphere appeared in 1946. In these smaller explosions the star loses only a minute fraction of its mass and survives to explode again.
Astrophysicists are fairly well satisfied that they can account for the explosions of supernovae. The novae and dwarf novae have presented more of a puzzle. I shall describe recent investigations that have provided important new information about these two classes of exploding star. The picture that emerges is quite astonishing. It appears that every dwarf nova--and perhaps every nova--is a member of a pair of stars. The two stars are so close together that they revolve around a point that lies barely outside the surface of the larger star. As a result the period of rotation is usually only a few hours and their velocities range upward to within a two-hundredth the speed of light,
Astronomers use the term "cataclysmic variable" to embrace the three general classes of exploding star: dwarf novae, novae, and supernovae. A cataclysmic variable is defined as a star that suddenly and unpredictably increases in brightness by a factor of at least 10. Dwarf novae are stars that increase in brightness by factor of 10 to 100 within a period of several hours and decline to their former brightness in two or three days. In this period they emit some 1038 to 1039 ergs of energy. At maximum brilliance a dwarf nova shines about as intensely as our sun, previously it had been only about a hundredth as bright. The number of outbursts ranges anywhere from 3 to 30 a year, but for any one star the intervals have a fairly constant value. Moreover, the maximum bright ness from outburst to outburst is the same within a factor of two for a given star. The dwarf novae are often referred to, after their prototypes, as U Geminornm or SS Cygni stars. (The stars of each constellation are designated by letters or numbers.) A subgroup of dwarf novae, called Z Camelopardalis stars, do not always descend to minimum bright ness between outbursts but may stay at some intermediate level for several months.
It is likely that in the paragraph that follows this passage the author will discuss ______.
选项
A、the characteristics of the explosion of a nova
B、supernovae
C、our sun as a dwarf nova
D、how the twin stars revolve
答案
A
解析
在这篇短文之后的自然段,作者很可能讨论新星爆炸的特征。作者在第二段告诉我们,他打算谈论最近为这两种爆炸的星球提供重要新资料的一些调查。他在第三段讨论了矮新星爆炸的一些特征,从逻辑上讲,他会在后面的一段讨论新星爆炸的特征。
转载请注明原文地址:https://kaotiyun.com/show/uo2O777K
0
考博英语
相关试题推荐
Thefactthatthegoldeneagleusuallybuildsitsnestonsomehighcliffs______italmostimpossibletoobtaintheeggsorthe
Thegovernmenthasdecidedtoreducea(n)______onallimports.
Writeashortcompositionof2504300wordsonthetopicgivenbelow.TOPIC:WhatIstheMostUrgentIssueFacingtheWorldP
Humansshouldnotdeveloptheireconomyatthe______oftheecologicalenvironment.
TheimprobablechainofeventsthatleadsAlexanderFleming1.______todiscoverpenicillinin1928isthestuffwhichscient
TheimprobablechainofeventsthatleadsAlexanderFleming1.______todiscoverpenicillinin1928isthestuffwhichscient
Fewerandfeweroftoday’sworkersexpecttospendtheirworkinglivesinthesamefield,______thesamecompany.
Measuringskinfoldthicknessisconsideredtobean_____methodforestimatingtheamountoffatonone’sbody.
AnAmericanliterarycritic,humorousjournalist,essayist,whosecomicskepticismabouthumanprogress,expressedwithpenetrat
Developingapeaceful,understanding,andsupportiverelationshipbetweenparentsandchildrenisnotaneasytask.Failurescana
随机试题
【背景资料】某施工单位承建某铁路客运专线双线隧道。隧道长度为2600m,起止里程为DK38+000~DK40+600。进、出口段浅埋,围岩为风化泥灰岩,岩体破碎,节理发育,裂隙水丰富,级别为Ⅴ级;洞身DK39+100~DK39+500段围岩级级为
某小区五楼刘某家的抽油烟机发生故障,王某与李某上门检测后,决定拆下搬回维修站修理。刘某同意。王某与李某搬运抽油烟机至四楼时,王某发现其中藏有一包金饰,遂暗自将之塞入衣兜。(事实一)王某与李某将抽油烟机机搬走后,刘某想起自己此前曾将金饰藏于其中,追赶前来,
处理肉芽过度增生的药物是
与可摘局部义齿稳定无关的是
A.曲泽B.间使C.内关D.大陵E.劳宫可用于治疗鹅掌风的穴位是
尿少,口干,皮肤弹性稍差,血压为11.3/7.7kPa,呼吸深快,口唇樱红,前囟门凹陷,心音低钝,肺无啰音,腹胀,四肢无力、稍凉,血钠132mmol/L。可能的诊断是
患儿,女,3岁,因发热3日伴流涕、咳嗽、流泪来诊。护士预诊时发现该患儿体温39.4℃,结膜充血、畏光流泪,并且在颊黏膜上出现柯氏斑,应首先考虑的疾病是()
甲公司是一家软件企业,80%的员工都是资深的程序员,则该企业适合于采用()。
心理咨询最终的目标是()。
Youwillhearanotherfiverecordings.Eachspeakerrecentlyattendedaninterview.Foreachrecording,decidewhatthespea
最新回复
(
0
)