Glossary term: Transit

Description: A transit is when, from the point of view of a particular observer, one body moves across the face of another, blocking the view of a small fraction of the background object. A transit viewed by one observer may not be seen by another observer viewing the same system from a different angle. In the Solar System both Mercury and Venus can sometimes transit across the face of the Sun when viewed from Earth. Moons orbiting Solar System planets are commonly seen to transit across the face of their host planet when viewed from Earth. Planets orbiting other stars (exoplanets) are often discovered when they transit their host star, blocking out a little of the star's light and making it appear to dim slightly when viewed from Earth. Transits can also be used to estimate the size of an exoplanet.

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Term and definition status: 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

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 Comments Attribution 4.0 International (CC BY 4.0) icons