The Search Engine Google is showing this animated doodle in many countries at Nothern hemesphere for marking the spring equinox , i-e the First Day of Spring The Spring equinox is also called as vernal Equinox.
An equinox is the moment in which the plane of Earth’s equator passes through the center of the Sun, which occurs twice each year, around 20 March and 23 September.
In nothern Hemishere, today is the spring equinox — 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 today, nighttime and daytime are each 12 hours.
You may also notice that on the equinox, the sun rises directly in the east and sets directly in the west, whereas at other times in the year, it appears off-center if you’re facing those directions.
Equinoxes are opposite on either side of the equator, so the autumnal (fall) equinox in the Northern Hemisphere is the spring (vernal) equinox in the Southern Hemisphere and vice versa.
And, Google is showing this another Doodle in Southern Hemisphere for makring the fall equinox, ie First Day of Fall 2017
The equinoxes are the only times when the solar terminator is perpendicular to the equator. As a result, the northern and southern hemispheres are equally illuminated.