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 the phases of the moon relate to the times it rises and sets, and why days and nights are not precisely equal on the equinox.
The exact minute of the autumnal equinox this year is 10:21 a.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 Northern or Southern Hemisphere is tilted towards the sun.
For observers, except those at the North and South poles, the sun on the equinox, from the Latin 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 waning gibbous moon will be high in the sky as the sun rises. After the evening session Venus may be visible low in the west, and a little later Saturn and Mars may be seen in the southwest.
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