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
Aspects of the Sun Since the beginning of time, human beings have been fascinated by the dramas unfolding in the firmament a
Aspects of the Sun Since the beginning of time, human beings have been fascinated by the dramas unfolding in the firmament a
admin
2013-04-25
35
问题
Aspects of the Sun
Since the beginning of time, human beings have been fascinated by the dramas unfolding in the firmament above--the shifting arch of the sun, the changing faces of the moon, the regular patterns of stars turning as the seasons change. The study of these subtle patterns and relationships in the cosmos evolved into Astronomy (or "law of the stars"), one of the oldest of the sciences. While different cultures, religions, and scientific theories all offer contrasting explanations for cosmic phenomena, there is one point on which they all agree: there would be no life on Earth if not for the sun.
Modern science has now proven that the sun, whose reliable path across the sky gives us the contours of our days and the duration of our nights, is the focal point of our solar system. The sun is, in fact, a star that is nearly 110 times the size of Earth and comprises more than 99% of the solar system’s mass, which creates enough gravitational pull to extend to the outer reaches of our solar system and keep all manner of matter (planets, asteroids, meteors and even dust) in orbit. Like other stars, the sun is made up of various gases, the most prevalent being hydrogen at around 74%, and helium at around 25%. Because the sun’s gravitational force inward is equal to that of its thermal pressure outward, it is in a state of hydrostatic equilibrium, which causes the sun to compress into a sphere.
While the sun is a near perfect sphere and appears to the naked eye as a precise and sharply defined yellow circle against the sky (hence its ancient astronomical symbol of a circle with a point at its center), it does not actually have a definite edge or boundary. Instead, the density of its gases decreases exponentially with distance from the core. Like most stars, the sun generates heat and energy via nuclear fusion, which takes place in the core at the center of the sun. This energy must travel through a number of different layers before it reaches the photosphere, the first layer of the sun’s atmosphere, where it escapes into space as sunlight. It is the photosphere that we see when we look at the sun. The layer is about 100 km thick, which is relatively thin compared to other solar layers, and is much cooler than the sun’s outermost atmospheric layer called the corona. One of the sun’s greatest mysteries is the incredible heat of the corona. Usually heat decreases with distance from the core; this is true for the sun until you reach the corona, which becomes suddenly hotter by a factor of nearly 200 times that of the photosphere. The exact process of heating and maintaining the corona is still one of the unsolved solar mysteries that continue to fascinate and perplex scientists today.
Another solar mystery is the curious nature of solar flares. Equivalent to millions of 100-megaton hydrogen bombs detonated simultaneously, solar flares are the most intense
and energetic explosions that occur in our solar system.
(A) These explosions occur on the sun’s photosphere and are difficult to view through the layer’s bright emissions, even with specialized equipment. Solar flares are directly linked to another more easily observable solar phenomenon--sunspots. With the invention of the telescope in 1608, astronomers were finally able to look into the face of the sun and see that it is not a perfect and unchanging yellow disc as they had expected, but that it is often marred by discernibleble mishes or dark spots.
(B) These dark areas are the coolest regions on the sun’s photosphere and are characterized by intense magnetic activity. The frequency of sunspot occurrences follows an eleven-year solar or sunspot cycle.
(C) At the minimum end of the cycle, there is very little sunspot activity and at the maximum end, there might be hundreds of visible sunspots. An increased number of sunspots indicates a correlated increase in solar flare activity.
(D) This period of activity can pose a serious danger to satellites and astronauts. One solar flare can emit enough magnetic energy to cause serious damage to a satellite, or change the satellite’s orbit. It can also shake the Earth’s magnetic field and cause dangerous surges in power lines, resulting in blackouts over large areas. Because of these dangers and our increasing reliance on satellites, it has become even more important for scientists to understand the nature of solar weather and to determine more accurate methods of predicting solar activity.
The word "It" in the passage refers to
选项
A、satellite.
B、solar cycle.
C、sunspot.
D、solar flar
答案
D
解析
指代关系题 这道题是寻找指示代名词的题目。在这里it用作主语,只要找到在前一句中it指代的名词就可以,而且it所在的句子和前面的句子都旨在说明太阳爆发的影响力,因此,solar flare为正确答案。
转载请注明原文地址:https://kaotiyun.com/show/gryO777K
0
托福(TOEFL)
相关试题推荐
TheInnovationofGroceryStoresA.Attheverybeginningofthe20thcentury,theAmericangrocerystoresofferedcomprehen
TheInnovationofGroceryStoresA.Attheverybeginningofthe20thcentury,theAmericangrocerystoresofferedcomprehen
TheInnovationofGroceryStoresA.Attheverybeginningofthe20thcentury,theAmericangrocerystoresofferedcomprehen
WhichmetalweretheCeltsusingatthebeginningofthefirstmillenniumB.C.?
WhichmetalweretheCeltsusingatthebeginningofthefirstmillenniumB.C.?
WhichmetalweretheCeltsusingatthebeginningofthefirstmillenniumB.C.?
WhichmetalweretheCeltsusingatthebeginningofthefirstmillenniumB.C.?
WhichmetalweretheCeltsusingatthebeginningofthefirstmillenniumB.C.?
ChooseTWOletters,A-E.WhichTWOaspectsdidthenewrulesattheendofthe19thcenturyfocuson?AcooperationBcompetitio
随机试题
临床体检时发现某患者肝脏肿大,根据你所学的知识,可能有哪些疾病的可能
Whichpartoftherenovationswilllikelybepostponed?
下述氨苄西林的特点哪一项是错误的
患儿,病程较长,反复不愈,小便不畅,神疲倦怠,气短懒言,舌质淡,苔白,脉沉细无力,指纹淡红。辨证用方是
下列药物中,以“胆碱受体阻断剂类抑酸剂”而实施消化性溃疡治疗的药物是
根据以下资料,回答下列问题。2012年,某省规模以上工业增加值10875亿元,比上年增长7.19/6,月度增速从1~2月的2.9%回升到10~12月的10%以上。大型、中型和小微型企业增加值分别为3074、3217和4584亿元,比上年分别增长8
建设项目的选址布局,不仅对建设项目本身的发展成败起着至关重要的决定性作用,而且对()也产生深远的影响。
一个人的一生,只能经历自己拥有的那一份欣悦,那一份苦难,也许再加上他亲自闻知的那一些关于自身以外的经历和经验。然而,人们通过阅读,却能进入不同时空的诸多他人的世界。这样,具有阅读能力的人,无形间获得了超越有限生命的无限可能性。阅读不仅使他多识了草木虫鱼之名
设循环队列的存储空间为Q(1:35),初始状态为front=rear=35。现经过一系列入队与退队运算后,front=15,rear=15,则循环队列中的元素个数为
在考生文件夹下,“sampl.accdb”数据库文件中已建立两个表对象(名为“员工表”和“部门表”)和一个窗体对象(名为“fEmp”)。试按以下要求顺序,完成表及窗体的各种操作。(1)设置“员工表”职务字段值的输入方式为在下拉列表中选择“经理”“
最新回复
(
0
)