Autumn begins Wednesday and here’s what you need to know

This is derived from the oldest understanding of an equinox, which suggests it is the day when daytime and night are of equal duration. This year’s harvest moon on the evening of September 27 is a super moon that will also display a rare total lunar eclipse. This happens as the sun reaches a point directly above the equator.

This discrepancy happens because the Earth is tilted 23.5 degrees on its axis and follows an elliptical (non-circular) orbit around the Sunday . This year, that will be a spot over the Indian Ocean about 1,200 miles east of Mogadishu, Somalia.

March 20, 2016 at approximately 04:30 UT (universal time) – Vernal equinox and first day of spring. Just check the almanac data for Wednesday morning and you’ll see that we still have 12 hours and 10 minutes of daylight.

The equinox is also marked at archeoastronomy sites worldwide.

Each September on the 21st, 22nd or 23rd, the sun is directly above the equator, marking the autumnal equinox. The subsolar point crosses the equator, moving northward at the March equinox and southward at the September equinox. Many more examples exist where ancient astronomers used architecture to mark the transition of the seasons. But whether autumnal or not, the September equinox means we’ll be seeing more night than day these next six months. This is because of the definition of sunrise and sunset, along with a bit of geometry.

Firstly, sunrise occurs when the top of the sun’s disk rises above the eastern horizon. In early autumn, these factors combine to make our days a few seconds shorter than 24 hours, in terms of the time it takes the sun to cross directly over our location – or pass over our longitude – from one day to the next.

Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and software engineer at Cisco Systems.