The public is invited to celebrate the spring equinox, which marks the end of winter and the beginning of spring, at the standing stones of the UMass Amherst Sunwheel on Thursday, March 20 at 6:45 a.m. and 6 p.m. These hour-long Sunwheel events, at sunrise and sunset, mark the astronomical change of seasons when days and nights are nearly equal in length all around the world.

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Observers standing at the center of the Sunwheel’s standing stones will see the sun rise and set over stones placed to mark the equinoxes, very close to due east and due west. Other structures around the world mark this astronomical change, such as the pyramid at Chichen Itza, Mexico and England’s Stonehenge.

At the gatherings, UMass Amherst astronomer Stephen Schneider will discuss the astronomical cause of the sun’s changing position during the gatherings. He will also explain the seasonal positions of Earth, the sun and moon, phases of the moon, building the Sunwheel, and answer questions about astronomy.

The exact time of the vernal, or spring, equinox this year is 5:01 a.m. Eastern Daylight Time on March 20 as the sun moves from the southern to the northern half of the celestial sphere, as seen from Earth. This marks the astronomical start of spring in the Northern Hemisphere and fall in the Southern Hemisphere. On the day of 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. 

On the day of the equinox, an observer located on Earth’s equator will see the sun pass directly overhead at local noon, and they will cast no shadow at noon. On any day other than the equinox, either the Earth’s Northern or Southern Hemisphere is tilted towards the sun. At Earth’s poles, the sun skims the horizon as it circles the sky over the course of the day, gradually rising at the North Pole to begin six months of daylight and slowly descending into six months of darkness at the South Pole. 

Just before sunset, the sun can be seen between the tall standing stones that form a portal on the west side of the Sunwheel. If it is clear before sunset, a solar telescope will be set up to safely observe the surface of the sun. 

The UMass Amherst Sunwheel is located south of McGuirk Alumni Stadium, just off Rocky Hill Road (the continuation of Amity St.) 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. 

For more information, please visit the UMass Amherst Sunwheel website.