Noun
the time for the earth to make one complete revolution around the sun, relative to the fixed stars
Source: WordNetHe also compared the lengths of the tropical year (the time it takes the Sun to return to an equinox) and the sidereal year (the time it takes the Sun to return to a fixed star), and found a slight discrepancy. Source: Internet
It is not clear if this would be a value for the sidereal year (actual value at his time (modern estimate) about 365.2565 days), but the difference with Hipparchus's value for the tropical year is consistent with his rate of precession (see below). Source: Internet
In 1437, Ulugh Beg determined the length of the sidereal year as 365.2570370.. Source: Internet
It is currently less than the sidereal year and its duration is very close to the mean Julian year of 365.25 days. Source: Internet