Mark the Fall Equinox and Extreme Moonset at the UMass Amherst Sunwheel

The Sunwheel during a fall equinox.

The public is invited to join University of Massachusetts Amherst astronomers at the standing stones of the UMass Amherst Sunwheel on Sunday, Sept. 22 at 6:30 a.m. and 6 p.m. for the fall equinox, and on Tuesday, Sept. 24 at 2:15 p.m. for the earliest setting of the moon.<_o3a_p>

From the Sunwheel, observers standing at its center will see the sun rise and set over particular stones placed to mark the equinoxes.<_o3a_p>

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.<_o3a_p>

The exact minute of the autumnal equinox this year is 8:43 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, and ushers in the beginning of fall in the Northern Hemisphere and spring in the Southern Hemisphere. People living on the equator see the sun pass directly overhead at local noon on the equinox. Six months of daylight begin at the South Pole and six months of nighttime at the North Pole. On every day other than the equinox, either Earth's Northern or Southern Hemisphere is tilted toward the sun.<_o3a_p>

If the skies are clear, a solar telescope will be set up before sunset to safely view the sun's surface. After the evening session, as it gets darker, there will be an opportunity to view Venus in its gibbous phase - seeing Venus in this phase was used by Galileo to prove that Venus goes around the Sun, not Earth.<_o3a_p>

For those interested in seeing the Moon at one of its extreme setting positions during this year of the major lunar standstill, there will be an opportunity on Sept. 24 starting around 2:15 p.m. If it is clear, telescopes will be set up at the Sunwheel to watch the Moon as it sets.<_o3a_p>

The UMass Amherst Sunwheel is located south of McGuirk Alumni Stadium, just off Rocky Hill Road (Amity Street) 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 would cancel the events, but the talks will be given if there are clouds or light rain. <_o3a_p>

For last-minute changes because of weather or other problems, please check the Sunwheel website at www.umass.edu/sunwheel.

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