AMHERST, Mass. (WWLP) – UMass Amherst is offering a celestial event that marks the end of summer and the beginning of fall.

Two public events will be held at the standing stones of the campus Sunwheel to observe sunrise and sunset on Wednesday, September 22, the Autumnal Equinox. Equinoxes (Vernal equinox in spring and Autumnal in fall) mark the astronomical change of seasons when days and nights are nearly equal in length around the world. The gatherings will be held in-person at 6:30 a.m. and 6:00 p.m.

UMass Amherst astronomer Stephen Schneider will explain the design of the Sunwheel and compare it to ancient calendar sites around the world, and discuss the astronomical cause of the sun’s changing position, the seasonal positions of the Earth, sun and moon, and mythology.

The change of seasons occurs when the sun crosses over the celestial equator from the northern hemisphere of the sky to the southern hemisphere. This year the exact minute of the autumnal equinox is 3:21 p.m. Eastern Daylight Time on Sept. 22, when fall will begin in the Northern Hemisphere and spring in the Southern. The sun rise due east and set due west, and stays up for 12 hours and down for 12 hours.

It also marks the beginning of six months of daylight at the South Pole and six months of nighttime at the North Pole. This is the origin of the word equinox, which means “equal-night.”

The UMass Amherst Sunwheel is located south of McGuirk Alumni Stadium, just off Rocky Hill Road (Amity St.) about one-quarter mile south of University Drive. Visitors to the Sunwheel should be prepared for wet footing, and mosquito repellent is highly recommended. Heavy rain cancels the events, but the talks will be given if there are clouds or light rain.