Glossary term: 行星

Description: 根据国际天文学联合会的定义，行星是指围绕恒星或恒星残余物运行的天体，其体积足够大，在自身引力作用下接近圆形，但质量不足以使其内核发生热核聚变。它还必须足够大，其引力才能将靠近恒星轨道的其他天体移走。因此，它们是寒冷的天体（与恒星相比），只能通过反射恒星的光在可见光波段发光，但它们也会在红外波段发光。在太阳系中，有八颗行星围绕太阳运行。行星基本上可能是岩石天体，比如内行星--水星、金星、地球和火星；也可能是主要由液态和气态物质组成的天体，有一个小的固态核心，比如外行星--木星、土星、天王星和海王星。太阳系之外的行星被称为太阳系外行星，简称系外行星。

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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

木星的自转，作者 Vishal Sharma，印度

Caption: 2021 年国际天文学联合会 (IAU) 天文教育办公室 (OAE) 天体摄影比赛，伽利略卫星类第三名：《木星的自转》，作者 Vishal Sharma，来自印度。这幅延时摄影作品精美地展示了木星的自转，以及画面右侧经过的两颗伽利略卫星。木星自转一圈只需不到 10 个小时，我们可以看到大红斑从左向右移动。在这短短的时间内，两颗卫星明显沿着它们的轨道前进了一段距离。这张照片是 2020 年在印度北部拍摄的。
Credit: Vishal Sharma/IAU OAE

License: CC-BY-4.0 Creative Commons 署名 4.0 国际 (CC BY 4.0) icons

The planet Jupiter, seen here as a bright disk, is orbited by the four Galilean moons, seen here as bright dots

Jupiter Moons Movie2, by Nicolas Hurez, Paul-Antoine Matrangolo, and Carl Pennypacker, United States of America

Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons. This sequence shows the orbit of the four Galilean moons around the planet Jupiter. Almost two entire orbits of the innermost moon, Io, can be seen, with the other moons (Europa and Ganymede, but in particular Callisto) being further away, orbiting noticeably slower. The images were obtained in 2018 with the Las Cumbres Global Observatory at different locations on Earth, allowing a continuous sequence of images over approximately half a week without gaps during the day. With clear skies and over the course of several nights, the motion of the Galilean moons can also be observed with binoculars (ideally steady your elbows on a surface).
Credit: Nicolas Hurez, Paul-Antoine Matrangolo and Carl Pennypacker/IAU OAE

License: CC-BY-4.0 Creative Commons 署名 4.0 国际 (CC BY 4.0) icons

Jupiter with coloured horizontal bands of clouds. The shadow of the moon Io is seen as a dark circle in the top left

Jupiter, Io and its shadow, by Ralf Burkart, Germany

Caption: First place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons. This time-lapse of Jupiter taken in 2017 from Germany beautifully illustrates the transit of one of the Galilean moons, Io, in front of Jupiter. As this is simply a moon casting a shadow on a planet it is equivalent to a lunar eclipse on Earth observed from further away. While the shadow of the moon is clearly visible from the beginning, it might be difficult to spot the moon itself against the background of the beautiful atmospheric bands of Jupiter the first time the video is seen. Watching it repeatedly allows appreciating the rapid motion and rotation in this fantastic observation.
Credit: Ralf Burkart/IAU OAE

License: CC-BY-4.0 Creative Commons 署名 4.0 国际 (CC BY 4.0) icons

水星

Caption: 这张图像是由信使号探测器（英文缩写：MESSENGER，意译为“水星表面、空间环境、环境化学与测距“）获取的水星表面拼接图像的合成图。信使号由美国宇航局于2004年发射，并在2011年至2015年间对水星进行了探索。
Credit: 美国国家航空航天局/约翰霍普金斯大学应用物理实验室/华盛顿卡内基研究所 credit link