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Right ascension of an astronomical object like a star in the celestial sphere is analogous to the longitude on Earth. Right ascension is usually measured in hours towards the east, which corresponds to 15° as 24 sidereal hours marks a complete circle of 360°. Just like longitudes, the right ascensions run through the celestial poles, which are the extension of the poles of the earth. Together with declination, they form the celestial coordinates.
Frequently Asked Questions
What is the reference of the right ascension?
The reference point for longitude on earth is the prime meridian chosen to be at the Royal Observatory at Greenwich, Britain. For the celestial longitude or right ascension, this arbitrary reference point of 0h right ascension is chosen to be at the vernal equinox on March 21, by convention.