Marking the beginning of spring, Google Wednesday published an animated doodle of a flower on the surface of the earth. The Spring Equinox, the first day of the season, falls on Thursday. Spring equinox is a day when the day and night are equal in length. The word equinox comes from the Latin for equal and night. Almost everywhere in the world, nighttime and daytime will be 12 hours long.
Equinox is used to mark the change of seasons, as the balance of light shifts to make days longer than nights. It marks the end of the winter season and informs people about the arrival of warmer days.
On the day of the equinox, the sun rises directly in the east and sets directly in the west. At other times in the year, it appears off-centre, if you’re facing those directions.
There are two equinoxes every year, in March and September. The March equinox marks the moment the sun crosses the celestial equator — the imaginary line in the sky above the Earth’s equator — from south to north and vice versa in September.
Earth’s axis is tilted at an angle of about 23.4 degrees in relation to the ecliptic plane, the imaginary plane created by the Earth’s path around the Sun. On any other day of the year, either the Southern Hemisphere or the Northern Hemisphere tilts a little towards the sun. But on the two equinoxes, the tilt of the Earth’s axis is perpendicular to the Sun’s rays, like the illustration shows.
The March equinox is often used by astronomers to measure a tropical year — the mean time it takes for the Earth to complete a single orbit around the sun.