AMHERST, Mass. – The public is invited to witness sunrise and sunset associated with the autumnal equinox among the standing stones of the UMass Amherst Sunwheel on Friday, Sept. 22 at 6:45 a.m. and 6 p.m. These Sunwheel events mark the astronomical change of seasons when days and nights are nearly equal in length in the Northern Hemisphere.
At the gatherings, UMass Amherst astronomer Stephen Schneider will discuss 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 answer questions about astronomy, such as how do the phases of the moon relate to the times it rises and sets? and why are days and nights not precisely equal on the equinox?
The exact minute of the autumnal equinox this year is 4:02 p.m. Eastern Daylight Time on Sept. 22. 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. 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. On any day other than the equinox, either the Earth’s Northern or Southern hemisphere is tilted towards the sun.
For observers, except those at the North and South poles, the sun on the equinox (for equi, “equal” and nox, “night”) 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, telescopes will be set up to permit observations of the Sun and other objects. At the morning session this fall, a gibbous Venus may be visible before sunrise. About half an hour after the evening session it may be possible to see Jupiter, Saturn and the crescent moon.
The UMass Amherst Sunwheel is located south of McGuirk Alumni Stadium, just off Rocky Hill Road about one-quarter mile west of University Drive. Visitors to the Sunwheel should be prepared for wet footing, and mosquito repellent is highly recommended. Heavy rain cancels the events. Donations are welcomed and will be used to help with the cost of additional site work at the Sunwheel and future events.