Last reviewed 22 Sept 2026 · 4 min read
The earth and its motions
- Rotation on its axis takes about 24 hours and gives day and night; the axis is tilted 23.5° from the vertical to the orbital plane.
- Revolution round the sun takes days, which is why a leap day is added every fourth year.
- The tilt, not the distance from the sun, causes the seasons.
| Event | Date | What happens |
|---|---|---|
| Summer solstice | 21 June | sun overhead at the Tropic of Cancer; longest day in the northern hemisphere |
| Winter solstice | 22 December | sun overhead at the Tropic of Capricorn |
| Equinoxes | 21 March, 23 September | sun overhead at the equator; day and night equal everywhere |
Latitude and longitude
Latitudes are parallels ( at the equator to at the poles); longitudes are meridians from the Prime Meridian at Greenwich. The earth turns in 24 hours, so of longitude equals one hour and equals four minutes. India's standard meridian is E, passing near Mirzapur, giving IST GMT hours. The International Date Line roughly follows .