Gatherings at the Sunwheel to Mark the Autumnal Equinox

The public is invited to observe sunrise and sunset associated with the day of the autumnal equinox among the standing stones of the UMass Amherst Sunwheel on Saturday, Sept. 23 at 6:30 a.m. and 6 p.m. 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.

UMass Amherst astronomer Stephen Schneider 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 (which means equi, “equal” nox, “night”) 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, and six months of daylight begin 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 Sunwheel in Amherst, observers standing at the center of the standing stones see the sun rise and set over stones placed to mark the equinoxes.

If the skies are clear, a telescope will be set up to view Venus in its crescent phase and possibly Jupiter and its moons before the morning session (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, and afterward there will be an opportunity to look at the waxing gibbous moon.