Today September 23, 2014 Google announced the First Day of Autumn 2014 with a Google Doodle on their homepage. The First Day of Autumn 2014 Google Doodle can be viewed in Japan, Turkey, Israel, South Korea, Greece, Germany, France, Spain, Canada, and the United Kingdom and on the Google United States homepages.
First Day of autumn 2014 – Autumnal equinox Google Doodle
The First Day of autumn 2014 Google Doodle is a short animation showing some trees and their leaves changing orange and yellow, typically associated with the season changes. As the animation goes on the all the leaves changes colors and the trees lose all their leaves.
The First Day of autumn is also known as the Autumnal equinox. There are two equinoxes every year – in September and March – when the sun shines directly on the equator and the length of day and night is nearly equal.
Seasons are opposite on either side of the equator, so the equinox in September is also known as the “autumnal (fall) equinox” in the northern hemisphere. However, in the southern hemisphere, it’s known as the “spring (vernal) equinox”.
What is an Equinox?
An equinox occurs when the plane of Earth’s Equator passes the center of the Sun. At that instant, the tilt of Earth’s axis neither inclines away from nor towards the Sun. The two annual equinoxes are the only times when the subsolar point—the place on Earth’s surface where the center of the Sun is exactly overhead—is on the Equator, and, conversely, the Sun is at zenith over the Equator. The subsolar point crosses the equator, moving northward at the March equinox and southward at the September equinox.
During an equinox, the Earth’s North and South poles are not tilted toward or away from the Sun, and the duration of daylight is theoretically the same at all points on Earth’s surface.
At an equinox, the Sun is at one of the two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and eclipticintersect. These points of intersection are called equinoctial points: classically, the vernal point (RA = 00h 00m 00s and longitude = 0°) and the autumnal point (RA = 12h 00m 00s and longitude = 180°).
The equinoxes are the only times when the solar terminator is perpendicular to the Equator. As a result, the Northern and Southern Hemispheres are illuminated equally.