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-> 彗星

彗星[View] [Edit] [History]
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RelationTargetTextual basis
typecelestial
name彗星
authority-wikidataQ3559
link-wikipedia_zh彗星
link-wikipedia_enComet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.

Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition.

Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma (the central part immediately surrounding the nucleus) and the tail (a typically linear section consisting of dust or gas blown out from the coma by the Sun's light pressure or outstreaming solar wind plasma). However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were called Manx comets. They are still classified as comets, such as C/2014 S3 (PANSTARRS). 27 Manx comets were found from 2013 to 2017.

there are 4584 known comets. However, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System (in the Oort cloud) is estimated to be one trillion. Roughly one comet per year is visible to the naked eye, though many of those are faint and unspectacular. Particularly bright examples are called "great comets". Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first to land a robotic spacecraft on a comet, and NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior.

Read more...: Etymology   Physical characteristics   Nucleus   Coma   Bow shock   Tails   Jets   Orbital characteristics   Short period   Long period   Oort cloud and Hills cloud   Exocomets   Effects of comets   Connection to meteor showers   Comets and impact on life   Fear of comets   Fate of comets   Departure (ejection) from Solar System   Volatiles exhausted   Breakup and collisions   Nomenclature   History of study   Early observations and thought   Scientific approach   Spacecraft missions   Classification   Great comets   Sungrazing comets   Unusual comets   Largest   Centaurs   Observation   Lost   In popular culture   Gallery  

The text above has been excerpted automatically from Wikipedia - please correct any errors in the original article.
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| 彗星的彗核、彗发和彗尾:

• 上排:深度撞击号拍摄的坦普尔1号彗星彗核和罗塞塔号拍摄的彗星67P

• 中排:霍姆斯彗星和星尘号拍摄的维尔特二号彗星彗核

• 下排:1997年于克罗埃西亚拍摄的海尔博普彗星和ISS上拍摄到的C/2011 W3彗星

|}

彗星(Κομήτης,Komet,Comet),俗称扫把星,是由冰构成的太阳系小天体(SSSB)。当其朝向太阳接近时,会被加热并且开始释气,展示出可见的大气层,也就是彗发,有时也会有彗尾。这些现象是由太阳辐射和太阳风共同对彗核作用造成的。彗核是由松散的冰、尘埃、和小岩石构成的,大小从P/2007 R5的数百米至海尔博普彗星的数十公里不等,彗尾可能延伸长达一天文单位。

彗星的轨道周期范围也很大,可以从几年到几百万年。短周期彗星来自超越至海王星轨道之外的柯伊伯带,或是与离散盘有所关联。长周期彗星被认为起源于欧特云,这是在古柏带外面,伸展至最近恒星一半距离上,由冰冻天体构成的球壳。长周期彗星受到路过恒星和银河潮汐的引力摄动而直接朝向太阳前进。双曲线轨道的彗星可能在进入内太阳系之前曾经被沿著双曲线轨迹被抛射至星际空间,则只会穿越太阳系一次。来自太阳系外,在银河系内可能是常见的系外彗星也曾经被检测到。

彗星与小行星的区别通常只在于存在著包围彗核的大气层,未受到引力的拘束而扩散著。这些大气层有一部分被称为彗发(在中央包围著彗核的大气层),其它的则是彗尾(受到来自太阳的太阳风电浆和光压作用,从彗发被剥离的气体、尘埃、和带电粒子,通常呈线性延展的部分)。然而,熄火彗星因为已经接近太阳许多次,几乎已经失去了所有可挥发的气体和尘埃,所以就显得类似于小的小行星。小行星被认为与彗星有著不同的起源,是在木星轨道内侧形成的,而不是在太阳系的外侧。主带彗星和活跃的半人马小行星的发现,已经使得小行星和彗星之间的差异变得模糊不清。

,已知的彗星有6,619颗,而且这个数量还在稳定的增加中。然而,这只是潜在彗星族群中微不足道的数量:估计在外太阳系的储藏所内类似的彗星体数量可能达到一兆颗。尽管大多数的彗星都是暗淡和不够引人注目的,但平均大概每年会有一颗裸眼可见的彗星,其中特别明亮的就会被称为「大彗星」。

在2014年1月22日,ESA科学家的报告首次明确的指出在矮行星谷神星,也是小行星带中最大的天体,有水气存在。这项检测是通过赫歇尔太空望远镜使用远红外线技术完成的。此一发现是出人意料之外的,因为彗星,不是小行星,才会有这种典型的「喷流萌芽和羽流」。根据其中一位科学家的说法:「彗星和小行星之间的区隔是越来越模糊了」。

古代也有彗星出现的记录,古人一般认为彗星是凶兆搜索。

Read more...: 命名和语源   研究的历史   早期的观测和推论   轨道的研究   物理性质的研究   近代的发现   物理性质   彗核   彗发   彗尾   喷流   与流星雨的关系   轨道特性   短周期   长周期   欧特云和希尔云   彗星的死亡   从太阳系排出   耗尽挥发物质   瓦解(分裂)   失踪   碰撞   命名规则   著名的彗星   大彗星   掠日彗星   不寻常的彗星   观测   对人类文化的影响   大众文化   相关条目   注释   进阶读物  

The text above has been excerpted automatically from Wikipedia - please correct any errors in the original article.

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URI: https://data.ctext.org/entity/746987 [RDF]

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