Summer Solstice at the UMass Sunwheel

To avoid crowds during the coronavirus pandemic, there will be no presentations at the UMass Amherst Sunwheel marking the start of summer. However, the public is invited to visit the site for sunrise and sunset to celebrate the longest days of the year. Visitors should wear masks and be prepared for the possibility of wet footing and mosquitoes.

At the solstice--stationary sun--the sun's rising and setting positions barely change for more than a week. From June 15 to 25, the shift of the sun will be less than one-fifth its own size. That's barely detectable without astronomical instruments, so any of those days would be great to visit the Sunwheel to see the alignment of the standing stones with the rising or setting position of the sun.

Pick a day with good weather as the sun rises or sets and stand at the center of the Sunwheel. The sun will touch the top of the tall stones in the northeast or northwest.

The astronomical start of summer is at 5:43 p.m. EDT on June 20 this year, the moment when the sun reaches its farthest northerly position in the sky, making June 20 the longest day of the year. Actually, day length from sunrise to sunset is only a few seconds shorter on the 19th and 21st, and changing conditions in the Earth's atmosphere can alter the angle of the sun's light enough that someone with a stopwatch might find a different day than the 20th is longest.

The local time for sunrise is officially 5:13 a.m., but the times listed in almanacs and online assume that you have an absolutely flat horizon, as you might see on the ocean. Given the local landscape, start looking for the sun around 20 minutes later. The sun will likewise set about 20 minutes earlier than the listed time of 8:30 p.m. There are also interesting things to see other than the alignment at the moment the sun touches the horizon. For example, when the sun is above the horizon you can see that it doesn't rise straight up, but at an angle that approximately equals our latitude. When the sun is slightly below the horizon, you may see a "sun pillar" when the sun reflects off the bottom of the clouds.