Do you know how time was tracked in Ancient India?
We all know that Days and Nights are formed by Earth rotating against its own axis. If earth is seen from north pole, we could see that Earth rotates counterclockwise, and we would watch daylight and darkness sweeping across our globe from east to west.
Earth also rotates around the sun in elliptical path. So is the moon, around the earth
In vedic period, the elliptical path of Moon’s rotation around earth was used to make the calendar. That was called Lunar Calendar.
Even Sun is continuously moving and If the Sun’s position in a constellation was used to make the calendar, That was called Solar calendar.
Even today, Hindu calendar uses the same.
In Lunar calendar, The Moon’s path was divided into 27 parts. All parts were equally divided. Each part rather sector was associated with a star that was having more influence on that sector. Since, the path was elliptical, moon would take little more time to traverse certain sectors. Depending on that, how much time a particular star is associated to a sector would influence Earth Or how much time moon would take to move from one sector to next, would be the star of the day. Due to this the lengths of the months vary from 29.2 to 31.2 days.
Similar is the concept with Solar calendar as well. In Solar calendar, day of the month begins with Suns lattitude being Zero, and last day of month would be when Sun is completing 360 degrees.
As per Lunar calendar :
Amount of Time Moon is nearest to Each star was calculated.
1 Muhurat = 48 mins
16 stars : 30 M :: 480 Muh
6 Stars : 45 M :: 270 Muh
6 stars : 15 M :: 75 Muh
1 Star : 6 M :: 6 Muh [Left out Abhijit Star. But it is still used for Muhurats/Lagnas]
Total 831 Muh
831 * 48 = 39888 mins
i.e 39888/60 = 644.8 Hrs
i.e. 644/24 = 27.7 days
If 28th star is to be left out , the calculation would come upto 27.3 days.
However, since earth is orbiting about Sun at the same time, it takes slightly longer for Moon to show same phase to Earth i.e. about 29.5 days.
To reconcile the differences between the solar and lunar calendars, an entire extra month is inserted about every 30 months. It is called adhika maasa.
In a month, a star could repeat more than once, since there were only 27 stars taking 27.3 days and months were 30/31 days long depending on moon.