Article - Forget Stonehenge: 5 Questions to Put Science Back in Summer Solstice

Huge crowds are expected to gather at Stonehenge in England this weekend to celebrate an annual astronomical event – the summer solstice. Officially beginning 5:45 Universal Time on June 21, the 2009 summer solstice marks the longest day of the year in the Northern Hemisphere.

Pagans and Wiccans gather at the solstice to honor the sun and to dedicate their service to the earth. But many solstice revelers use the extra hours of sunlight as an excuse to party. According to an article in The Guardian, the Wiltshire police are bringing horses, drug sniffing dogs and an unmanned drone to control the 30,000 people expected to descend upon the ancient ruins. The article goes on to say that “peace-loving” Druids are taking their celebrations elsewhere to avoid the unruly throngs.

I don’t blame them.

I can’t think of anything less spiritual than crowding shoulder-to-shoulder with a bunch of hippies and wannabe wizards who want to get drunk watching the sun come up. But there's plenty of science surrounding the solstice. So here are the answers to five commonly asked questions about the solstice to add a bit of science fun to your celebration.

When is the solstice? I mentioned earlier on that the solstice will occur at 5:45 Universal Time on June 21, 2009. Is UT the same as Greenwich Mean Time? Find out at this website from EarthandSky.org. Have the kids, or your mathematically challenged spouse, try to figure out exactly when the solstice will occur where you live. Be warned: the start time may have passed by the time you figure it out, but it is worth trying. If you wonder when the solstice will occur next year or when it occurred last year, check the calendar of Equinoxes, Solstices, Perihelion, and Aphelion for 2000 to 2020 from the US Naval Observatory. The USNO also has an astronomical almanac online, scads of data I would not know what to do with, and a lovely little newsletter that you must read called “The Sky This Week,” that explains astronomy in layman’s terms. I don’t know who writes “The Sky This Week,” but the thing is absolute poetry and will make you fall in love with astronomy all over again.

Why do we have solstices? We have a solstice because of our “wonky” planet Earth, proclaims the BBC.com. The British broadcasters have an excellent page explaining in simple terms why we have seasons, when they occur, and where the sun and the Earth are positioned during all of this. The solstices occur due to the tilt of the earth on its axis –that imaginary line that runs through the center of the globe. At the summer solstice, June 21, the earth is tilted 23 degrees toward the sun and the northern hemisphere receives the most sunlight. At the winter solstice, December 21, the planet is tilted 23 degrees away from the sun and the southern hemisphere basks in the sun’s glory. Right now, my friends in Australia are bundling up for a chilly winter, while I am pulling out the shorts and tank-tops

Why isn’t it hottest at the summer solstice? If the summer solstice is the longest day, you would think that it also would be the hottest day. It isn’t and, as EarthandSky.org explains, it has to do with a phenomenon called the “lag of seasons.” Just as adding hot water to a cold bath does not instantaneously heat it up, the sun needs a little time to warm up the earth. Some snow and ice must melt before the planet can really get toasty. Check the thermometer in late July and August, and note that, even though the days are getting shorter then, the temperatures will be going up.

What does the earth look like from space at this very moment? John Walker, a programmer and blogger, has developed some visual software that allows you to view the Earth, both the day and night regions, at this very moment from the perspective of the moon or the sun. You also can set the longitude, latitude and altitude as well as view the Earth as if from an orbiting satellite or hovering 7 km above one of a couple hundred cities on earth. It’s not like Google Earth, but I still like this viewer. Pretend you are inside the International Space Station looking down on the planet below and watch the sun rise from there.

Does the sun “rest” for three days during the solstice? Astronomers and mystics have been asking this question since ancient times. If you observe the sun near the solstices, it certainly appears to set in the same spot every day. This article by Asger Mollerup describes the use of sundials and specifically the gnomon (the part that stands up) to track the sun during a solstice, as well as during other astronomical events. Mollerup has posted some fascinating photos that show the summer sun setting on the horizon and appearing to rest in the exact location for three days straight. He also has photos and descriptions of astroarchaelogical sites throughout Southeast Asia (Thailand, Laos, and Cambodia); just in case you thought the Mayans and the Druids had the market cornered on sun worship.