AMHERST, Mass. – The public is invited to view the sunrise and sunset associated with the spring equinox among the standing stones of the UMass Amherst Sunwheel on Wednesday, March 20 at 6:45 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.
From the Sunwheel in Amherst, observers 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, as well. For example, the Mayans at their main pyramid at Chichen Itza built staircases at such an angle that on the equinox, sunlight casts a shadow that looks like a giant snake descending the stairs.
At the hour-long gatherings, 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. On the equinox (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 almost everywhere in the world. Observers at Earth’s poles see the sun skimming around the entire horizon as six months of daylight begin at the North Pole and six months of night at the South Pole.
The exact time of the spring or vernal equinox in western Massachusetts this year is at 5:58 p.m. on March 20. This marks the moment when the sun crosses the celestial equator, traveling from south to north. An observer located on the Earth’s equator will see the sun pass directly overhead at local noon on this day. After the spring equinox, Earth’s Northern Hemisphere is tilted toward the sun.
If the skies are clear during the evening session, a solar telescope will be set up to safely observe the sun before sunset. The full “sap” or “worm” moon will rise just minutes after sunset almost exactly due east. Names for the full moons come from cultural and natural events at that time of year, such as the running of sap or the emergence of worms from the thawing ground.
The UMass Amherst Sunwheel is located south of McGuirk Alumni Stadium, just off Rocky Hill Road about one-quarter mile west of University Drive. Visitors to the Sunwheel should be prepared for especially wet footing this year. Rain or blizzard conditions cancel the events.