UMass Amherst Sunwheel and Sky-Watching Events to mark the Autumnal Equinox on September 23

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The public is invited to join UMass Amherst astronomer Stephen Schneider among the standing stones of the campus Sunwheel to observe sunrise and sunset on Saturday, Sept. 23 — the autumnal equinox. These Sunwheel events mark the astronomical change of seasons with presentations explaining how the Sunwheel marks the changing position of the sun and moon as seen from Earth. The gatherings will be held in person at 6:30 a.m. and 6:00 p.m.

The UMass Amherst Sunwheel

From the UMass Sunwheel in Amherst, observers standing at its center see the sun rise and set over particular stones placed to mark the equinoxes.

Schneider will explain the design of the Sunwheel and compare it to ancient sites around the world. He will discuss the astronomical cause of the sun’s changing position during the approximately hour-long gatherings. He will explain why days and nights are nearly equal on the equinox (equi means “equal,” and nox, “night” in Latin) and answer other questions about astronomy.

The exact minute of the autumnal equinox this year is 2:50 a.m. Eastern Daylight Time on Sept. 23. This marks the moment that the sun crosses the celestial equator from north to south as seen from Earth, ushering in the beginning of fall in the Northern Hemisphere. People living on the equator see the sun pass directly overhead at local noon on the equinox. Six months of daylight begins at the South Pole and six months of nighttime at the North Pole. On any day other than the equinox, either Earth’s Northern or Southern Hemisphere is tilted toward the sun. For observers, except those at the North and South Poles, the sun on the equinox rises due east and sets due west and stays up for 12 hours and down for 12 hours. From the

If the skies in Amherst are clear, a telescope will be set up before the morning session to view Venus in its crescent phase and possibly Jupiter and its moons (beginning about 6 a.m.). During the evening session, a solar telescope will be set up before sunset to safely view the sun’s surface. Afterward there will be an opportunity to look at the waxing gibbous moon.

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.

This story was originally published by the UMass News Office.