Glossary term: Radial Velocity

Description: Radial velocity is the motion of an object towards or away from an observer in the line of sight. This depends on the position of the observer, with only the component of the object's velocity which moves towards or away from the observer making up the radial velocity viewed by that observer. It is commonly measured by looking for the Doppler shift in lines in the object's spectrum. Objects orbiting other objects have radial velocities that vary throughout their orbit. This effect can be used to discover unseen objects such as planets orbiting other stars. More massive bodies induce faster orbital velocities on objects orbiting them. This effect means radial velocities can be used to estimate the masses of planets, stars, star clusters, galaxies, and galaxy clusters.

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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".