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UMass to host sky-watching events on autumnal equinox

  • The Sunwheel at UMass Amherst. file photo


Staff Reports
Wednesday, September 12, 2018

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 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 in the Northern Hemisphere.

UMass 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 the Earth, sun and moon, and answer questions about astronomy, such as why sunrises and sunsets are at different times for the fall and spring equinoxes and why days and nights are not precisely equal on the equinox.

The exact minute of the autumnal equinox this year is 9:54 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 the 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 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, telescopes will be set up to permit observations of the sun and other objects during the evening session. About half an hour after sunset, it may be possible to view the crescent Venus, which is passing Earth in its orbit, moving from the evening to the morning sky. Jupiter, Saturn and Mars are also visible in the evening sky.