Gathering at the Sunwheel to Mark the Autumnal Equinox

The public is invited to join UMass Amherst astronomer Stephen Schneider to observe sunrise and sunset on the day of the autumnal equinox among the standing stones of the campus Sunwheel on Thursday, Sept. 22 at 6:30 a.m. and 6 p.m. These Sunwheel events mark the astronomical change of seasons when days and nights are nearly equal in length around the world.

From the Sunwheel in Amherst, observers standing at the center of the standing stones see the sun rise and set over standing stones placed to mark the equinoxes. Prof. Schneider will explain the design of the Sunwheel and compare it to ancient calendar sites around the world. He will explain the astronomical cause of the sun's changing position during the hour-long gatherings. He will also explain the seasonal positions of Earth, the sun and moon, and discuss various myths and confusing aspects of the equinox.

Astronomers mark the change of seasons as the moment when the sun crosses 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. Fall begins in the Northern Hemisphere and spring in the Southern. On the day of the equinox, an observer located on Earth's equator will see the sun pass directly overhead at local noon, and it marks the beginning of six months of daylight at the South Pole and six months of nighttime at the North Pole.

For people around the world (other than those at the North and South Poles) on the equinox, the sun rises due east and sets due west and stays up for 12 hours and down for 12 hours. 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.

For last-minute changes because of weather or other problems, please check the Sunwheel website at www.umass.edu/sunwheel.