AMHERST – The public is invited to witness sunrise and sunset associated with the autumnal equinox among the standing stones of the UMass Amherst Sunwheel on Wednesday, Sept. 23 at 6:45 a.m. and 6 p.m. These Sunwheel events mark the astronomical change of seasons when days and nights are of nearly equal length in the Northern Hemisphere.
At the gatherings, which have attracted more than 10,000 visitors over the past 18 years, 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 in astronomy such as the definition of blue moon, supermoon, and why Sept. 23 is celebrated despite the fact that Sept. 17 is actually the shortest day of the year.
The exact time of the autumnal equinox this year is 4:20 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. On the day of the equinox, an observer located on the Earth’s equator will see the sun pass directly overhead at local noon. On this the day the sun rises into the sky to be visible for six months as seen from the South Pole, and it sets for six months as seen from 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 crescent Venus may be glimpsed before the sun rises, and at the evening session a waxing gibbous moon will be up.
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 or blizzard conditions cancel the events. Donations are welcomed and will be used to help with the cost of additional site work at the Sunwheel and future events.
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