AMHERST, Mass. - The public is invited to witness sunrise and sunset on the day of the spring equinox among the standing stones of the UMass Amherst Sunwheel on Monday, March 20 at 6:40 a.m. and 6 p.m. These Sunwheel events mark the astronomical change of seasons when days and nights are nearly equal in length around the world. Rain or severe weather cancel the events.
At the hour-long gatherings, which have attracted more than 10,000 visitors over the past 19 years, UMass Amherst astronomer Stephen Schneider will discuss the astronomical cause of the sun's changing position. He will explain the seasonal positions of the sun, moon and Earth, and answer questions about astronomy. If the skies are clear, the third-quarter moon will be visible during the morning session and an extremely thin crescent Venus may be visible just above the horizon after sunset. A solar telescope will be available to safely observe the sun before sunset.
The exact time of the spring or vernal equinox in western Massachusetts this year is at 6:29 a.m. Eastern Daylight Time on Monday, March 20. This ushers in the beginning of spring and is also the day the sun rises into the sky to be visible for six months as seen from the North Pole, and the day it sets for six months as seen from the South Pole. An observer located on the Earth's equator will see the sun pass directly overhead at local noon. On any day other than the equinox, either the earth's Northern or Southern Hemisphere is tilted towards the sun.
On the equinox, Latin for equi "equal," and nox "night," the sun rises due east and sets due west and stays up for 12 hours and down for 12 hours (except for observers at the poles). 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. Other structures around the world mark this astronomical change. For example, the Mayans built staircases at their main pyramid at Chichen Itza at such an angle that on the equinox, sunlight cases a shadow that looks like a giant snake descending the stairs.
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 especially wet footing this year. Donations are welcome and will be used to help with the cost of additional site work at the Sunwheel and future events.