Tropical vs sidereal year
- ऋतवः स्वभावतः सौराः, न चान्द्राः।
- वर्षमाने विभागद्वयम् - Tropical (सायन-वर्षम्) vs sideral इति।
- Tropical year depends on earth’s axis. Siderial year depends on sun’s position against the background of stars (PS: sun itself is moving).
- Tropical year is 20 minutes 24 seconds (~ 3.9003e-5 tropical year) shorter than sidereal year, because earth’s axis of rotation is also moving besides the earth itself. (Intro videos: YT).
- Tropical year gets the season’s right, but places the earth on the opposite side of the sun eventually in 15000 CE.
- Tropical year is approximately 365.242189 days long on average. Its length changes slightly over time.