History of the Solar Year

Celestial wheel turns in 360 days
Dirgatamas~2600BCE

True year is between 365 & 366
Yajur,2400BCE

366 for civil use!
Lagadha,1370 BCE

Correction month in 2.5 yrs!
Kautilya,300BC

365.2588
Surya Sid-200CE

365.2585
Aryabhata

Modern sidereal-365.25636
1560-Christopher Clavius sends several Jesuits to Kerala to learn Jyotisha, accurate trignometric tables etc

1582-Gregorian calendar adopted with Indian Ahargana system('Julian numbers'); 11 October days dropped

1752-British empire adopts Gregorian

1956-India adopts Gregorian
Aryabhata's value is off by just 3mins 20sec. The true solar year is the sidereal, not the Tropical one which the Gregorian continues to use, along with many unscientific & arbitrary absurdities such as '28' Feb days.

'Jan 1' has no significance whatsoever. Well, Happy new year!
For getting clarity on this complicated topic, I recommend Prof Kosla Vepa's encyclopedic volumes.

Further reading- https://twitter.com/JoeAgneya/status/923818607154315269?s=20
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