Sun is the king of all planets. All planets revolve around it. Astrology considers Sun a planet, but in terms of geography it is a star. Revolution of Earth around the Sun changes day, night and Ayan ( Uttrayan and Dakshinayan).
The secret of the sidereal time is hidden in the process of circumambulation of Sun by Earth. Earth rotates on its axis for 24 hours. Earth rotates 360 degrees on its axis in 24 hours revolving around the Sun. This completes one whole day called the solar day. Ideally, it is said that 24 hours is the rotation time, though this duration is 23 hours, 56 minutes and 4.09 seconds. The remaining 3 minutes 56 seconds are considered as the sidereal day, which is the remaining part of the solar day. In short, a sidereal day can be defined as the time taken to rotate from one time gap to another time gap from the middle point. The remaining time between this is called the sidereal time.
Importance of Sidereal Time in Astrology
One Sidereal day has 24 sidereal hours. According to the method of calculation of time, this is considered the sidereal time. The sidereal time is very important in astrology. This is because the situation of zodiac during this period in any country or place everyday will be same in the next cycle. That means the position of signs in one sidereal time will be same in the next 24 hours. The position of the Ascendant, tenth and the fourth house will also be same. This is the reason why astrologers need accurate sidereal time while they prepare birth-chart. It is only through this that they will get right results.
The Sidereal Day is Longer Than the Solar Day: Why?
The sidereal day is longer than the Solar day, because Earth completes one cycle in one sidereal day. However during this period, Sun rotates in zodiac for 10 times. So Earth has to rotate more to reach to the position of Sun. Earth takes 4 minutes more for this. That means Sun rotates for 360.9860.