Glossary term: Right Ascension (RA)

Description: Right ascension is a celestial coordinate in the equatorial coordinate system that is fixed relative to the fixed stars (the second coordinate is declination). The points directly above Earth's equator form the celestial equator, the point directly above Earth's geographic North Pole is the celestial North Pole (similarly for the South Pole). Define longitude and latitude on the resulting sphere so that each fixed star position has constant longitude and latitude values. As the analog of the Greenwich meridian on Earth, choose the March equinox, where the Sun's apparent path crosses the celestial equator in spring. This longitude is called right ascension. Its values increase to the east. The longitude angle is typically stated as a time, with 24 hours corresponding to 360 degrees.

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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".