Glossary term: 軌道

Description: 軌道是在一個系統中運動的天體圍繞該系統質心的軌跡，由系統中天體之間相互施加的萬有引力引起。在太陽系等系統中，中心天體的質量遠大於其他天體，質心位於質量最大的天體（在太陽系中為太陽）內部或其附近。在雙星系統中，恆星軌道的質心通常位於兩顆恆星之間。

軌道的形狀通常呈橢圓形，系統的質心位於橢圓的一個焦點上。軌道的大小和形狀由橢圓的半長軸和離心率決定。離心率越大的軌道橢圓度越高。太陽系中大多數行星軌道的離心率都非常接近零，例如金星（0.007）和地球（0.017）。而離心率較大的例外有水星（0.206）和矮行星冥王星（0.244）。

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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

This is an automated transliteration of the simplified Chinese translation of this term

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".

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木星的自轉，作者 Vishal Sharma，印度

Caption: 2021 年國際天文學聯合會 (IAU) 天文教育辦公室 (OAE) 天體攝影比賽，伽利略衛星類第三名：《木星的自轉》，作者 Vishal Sharma，來自印度。這幅延時攝影作品精美地展示了木星的自轉，以及畫面右側經過的兩顆伽利略衛星。木星自轉一圈只需不到 10 個小時，我們可以看到大紅斑從左向右移動。在這短短的時間內，兩顆衛星明顯沿著它們的軌道前進了一段距離。這張照片是 2020 年在印度北部拍攝的。
Credit: Vishal Sharma/IAU OAE

License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (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 姓名標示 4.0 國際 (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 姓名標示 4.0 國際 (CC BY 4.0) icons

beta Pictoris b moves from bottom right towards the center of the image, reappearing 22 months later on the top left

The orbit of beta Pictoris b

Caption: This series of images shows the orbital motion of the extrasolar planet (exoplanet) beta Pictoris b. The planet is the bright dot in each image. The planet's host star is hidden behind the black circle in the middle of each image. This is done to remove the much brighter host star which would otherwise drown out the light from the planet. The planet's orbit is viewed edge-on. Seeing the orbit from this perspective makes it look like the planet moves along a straight line. Between February 2015 and November 2016 beta Pictoris b appears to move closer and closer to its host star. The planet then moved so close to the star that it was not seen for almost two years, after which it reappeared on the other side of the star.
Credit: ESO/Lagrange/SPHERE consortium credit link

License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (CC BY 4.0) icons

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