An Encounter With Halley's Comet

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图注： This image shows the solid core, or nucleus, of Halley’s Comet, captured in 1986 by the European Space Agency spacecraft Giotto during its flyby of the comet in the inner Solar System. The nucleus appears irregular and potato-shaped, measuring roughly 15 kilometers (about 9 miles) across, and is composed of a mixture of ice, dust, and rock. Unlike the glowing fuzzy cloud (coma) and long tail that make comets visible from Earth, the nucleus itself is dark and difficult to see until a spacecraft passes close enough to take detailed images. Halley’s Comet is one of the best-known comets because it returns to the inner Solar System approximately every 76 years, allowing generations of astronomers to observe it repeatedly. The material that is released from the nucleus as the comet warms near the Sun forms a glowing coma and long tails of gas and dust, and over many returns leaves trails of debris that produce meteor showers on Earth, such as the Eta Aquarids in May and the Orionids in October.
来源： NASA/ESA/Giotto Project
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词汇表: 彗发 , 彗星 , 彗核 , 哈雷彗星

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Halley's Comet

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图注： Halley’s Comet, is a well-known periodic comet, named after the English astronomer Edmond Halley. It has an orbital period of approximately 75 years and is visible from Earth with the naked eye when it passes through the inner solar system. The image shows Halley’s Comet, officially designated 1P/Halley, with a tail of gas and dust streaming away from the Sun. It was taken from the La-Silla-Observatory in Chile in 1986 during Halley's Comet's last visit to the inner solar system. The stars in this image appear elongated or as lines of three different colored dots as image was created from three separate observations in different colors of light and the telescope was tracking the comet, which was moving very slightly compared to the background stars. Note that the comets tail does not point in exactly the same direction as the elongation of the stars. This shows us that the comet tail is not always behind the comet, but instead pointing away from the Sun. The comet passes its perihelion (closest distance to the Sun) at a distance of around 0.59 astronomical units, right between the orbits of Mercury and Venus. Beyond Neptune, it reaches its aphelion (furthest distance from the Sun) at a distance of approximately 35 astronomical units. Halley's Comet reached aphelion in December 2023 and is now moving inwards again. It is expected to be seen with the naked eye from Earth again in mid-2061.
来源： ESO
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词汇表: 远日点 , 彗星 , 彗尾 , 哈雷彗星 , 近日点

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海尔-波普彗星

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图注： 彗星 C/1995 O1（海尔-波谱）的图像，拍摄于 1997 年 4 月 4 日，曝光时间为 10 分钟。显示的视场约为 6.5°x6.5°。明亮的彗尾上延伸出两条尾巴：一条白黄色的尘埃尾巴和一条始终指向远离太阳的方向蓝色的气体尾巴。
来源： E.Kolmhofer, H. Raab; Johannes Kepler Observatory, Linz, Austria
来源链接

词汇表: 彗星 , 彗尾
分类： 太阳系

授权许可： 知识共享许可协议 Attribution-ShareAlike 3.0 Unported 知识共享许可协议 Attribution-ShareAlike 3.0 Unported 图标

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Comet Shoemaker-Levy After Crossing Jupiter's Roche Limit

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图注： This panoramic image captured by the Hubble Space Telescope shows fragments of Comet Shoemaker–Levy 9. This comet was discovered in 1993 as the series of fragments you see here. These fragments were orbiting Jupiter. It is thought that at some point in the previous few decades the whole, unfragmented comet had been gravitationally captured by Jupiter. Then in 1992 the comet passed within Jupiter’s Roche limit. Astronomical objects exert gravitational forces on each other. The closer one is to an object, the larger the force. As astronomical objects have a real physical size, the side of an object closer to another object will feel a stronger gravitational force from that other object than the more distant side. The gravitational stretching distorts the object. This gravitational stretching force is known as the tidal force. When an object is close enough to a large body like Jupiter, the object will feel such a large tidal stretching force that it will overcome the internal gravitational force holding the object together, ripping it to shreds. The distance from the larger body within which this occurs is known as the Roche limit. When Shoemaker–Levy 9 crossed Jupiter's Roche limit in 1992, the tidal force pulled the comet into separate fragments. Here we see these fragments in a chain as they orbited Jupiter in May 1994. Later in July 1994 the comet fragment plunged into Jupiter’s atmosphere over the course of a week in a spectacular series of impacts. This event provided scientists with a rare opportunity to witness an impact unfolding in real time.
来源： NASA, ESA, and H. Weaver and E. Smith (STScI)
来源链接

词汇表: 洛希极限 , 潮汐力

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67P/丘留莫夫-格拉西缅科彗星

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图注： 67P/Churyumov-Gerasimenko 彗星的彗核是一个由冰冻物质和尘埃混合而成的 "脏雪球"。它的形状像两个大耳叶：一个体积为4.1 千米 × 3.3 千米 × 1.8 千米，另一个为 2.6 千米 × 2.3 千米 × 1.8 千米。这些耳叶由一座小桥连接在一起。当这样的彗星核接近太阳时，它的冰冻物质会被加热，变成气体。这些气体与内部的尘埃共同组成了彗星特有的彗发和彗尾。
来源： 欧空局/Rosetta/NAVCAM
来源链接

词汇表: 彗星 , 彗核
分类： 太阳系

授权许可： 知识共享许可协议 Attribution-ShareAlike 3.0 IGO 知识共享许可协议 Attribution-ShareAlike 3.0 IGO 图标

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