Measurement of time.
How current calendars can't match ancient Hindu timekeeping.

Why a day isn't always 24 hours long

Why a year doesn't have 365.25 days

#science #astronomy #Time
1/n
How long does a day last everyday? 24 hours? Wrong.

We define day as the time taken by Earth to complete one rotation around its axis.
But with respect to what is the measurement made? 2/n
Since Earth is also revolving around Sun while it is rotating, it needs to rotate a little extra when rotation is measured w.r.t. sun (solar day) than a distant star (sidereal day)
3/n
You come back to same point after rotation in 24 hrs when measured w.r.t Sun but takes 23 hours 56 min when compared to very distant stars.

4/n
Is that all? No.

Earth rotates in an oval orbit around sun. And moves faster at Perihelion and slower at Apihelion. This changes the duration of day as measured w.r.t Sun (Solar day) through the year....
5/n
This variation in the duration of Solar day through the year is described using the equation of time.
6/n
Now compare this with the ancient Hindu calendar method of Tithi.

A Tithi is exact measurement of moon in sky by 12 degrees. And due to equation of time, it varies in time but each lunar month is precisely 30 tithis of 12 degrees = 360 degrees

7/n
That is why a Tithi doesn't last for exactly same time duration - varies from 19 hours to 26 hours.
But is precisely always 12 degrees. Synchronized at Amavasya.
8/n
But Lunar year (12*30 lunar tithis) has almost 10.87 days less in a year. So, after every 32.5 month an extra month of 11 days is added to sync lunar and solar calendars.

This is the auspicious Hindu month called - Aadhik Maas dedicated to dharma, teerthas. 9/n
So while modern Gregorian calendars can't handle equation of time....
Ancient Hindu calendars had it inbuilt in it. The End.
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