Sky science
Radial Velocity
Direct answer
Radial Velocity is the component of an object’s velocity toward or away from the observer along the line of sight.
It measures motion along the viewing direction.
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At a glance
- Found in
- Astronomy & Skywatching
- Related
- Stellar Parallax, Proper Motion, Light-Time Correction, Orbital Elements
It measures motion along the viewing direction.
A scientific orientation to scale, light, or motion; the article supplies the precise definition.
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The story behind Radial Velocity
Spectroscopic Doppler shifts made radial velocity a major astronomical measurement.
A one-minute story
The Wandering Stars
How the moving planets were watched, named and found, and what a transit is.
Why Radial Velocity matters
Radial Velocity reveals stellar motion, binary orbits, galaxy dynamics, and unseen planets.
How to read Radial Velocity
State the reference frame and sign convention used for the velocity.
Radial Velocity in practice: an example
Periodic stellar velocity shifts can indicate an orbiting exoplanet.
Where readings of Radial Velocity go wrong
Radial velocity omits motion across the sky and can include non-orbital spectral effects.
Sources and editorial method
Research references used for this entry include:
- European Southern Observatory: Spectroscopy - Observatory explanation of spectra and the physical information encoded in astronomical light.
- NASA Science: Universe Glossary - NASA definitions for common stellar, galactic, orbital, and high-energy astronomy terms.
- Source
- The Great Almanac Dictionary
- Category
- Astronomy & Skywatching
- Last updated
- 2026-09-26
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Common questions
What is radial velocity?
Radial Velocity is the component of an object’s velocity toward or away from the observer along the line of sight.
What do people get wrong about radial velocity?
Radial velocity omits motion across the sky and can include non-orbital spectral effects.
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