The purpose of the giant stone megaliths that prehistoric man dotted over the world’s countryside has long produced intense speculation. The most favored explanation is that they represent Stone Age computers used by ancient agrarian societies to track the motions of the moon and sun and thus the change of seasons.

The book “Stonehenge Decoded” by Gerald Hawkins makes this argument for the most famous megalith of all, and “Celestial Geometry” by Ken Taylor covers many different megaliths both in Europe and around the world.

Researchers in Scotland have claimed they have definitive proof that a cross-shaped megalith at Callanish on the Isle of Lewis, constructed by Stone Age people over 5000 years ago had just such a purpose. They did a statistical 3-D analysis of the megalith and its environment with the sky as it would have appeared at that time.

Sun and moon movements aligned with the megalith that could also track a cyclical lunar event that occurs every 18.6 years. One of the researchers, Dr. Gail Higginbottom of the Australian National University, said, “Knowing the times of the winter and summer solstice, the changing length of day, and the coming of colder or warmer seasons was vital to ancient agrarian societies.”

Focus on the planets

Mercury rises in the east about a hour and a half before sunrise at mid-month. As September nears its end, Mercury is about a quarter of the way up on the horizon and provides the best morning viewing for the year. On Sept. 28, the thin crescent moon passes just below Mercury.

Venus can be found in the west as darkness falls. On Sept. 3, Jupiter, Venus and the crescent moon forms an ascending diagonal line. Venus will grow more prominent as the month passes.

Mars rises in the south during the evening hours near the bright star Antares. On the evening of Sept. 8, Mars, Saturn and Antares form a close triangle with the passing moon directly above Saturn.

Jupiter rises low on the western horizon as darkness falls and by mid-month sets a half hour after the sun and is essentially lost to view. On Sept. 2, an extremely thin crescent moon is situated just to the left of Jupiter.

Saturn rises in the west shortly after sunset and sets around midnight. In this brief window, Saturn’s rings are nearly at maximum tilt for excellent viewing as is its major moon, Titan.

Uranus rises in the southeast around midnight in Pisces where its blue-green disk is viewable by telescope.

Neptune comes into view in the southeast at dusk, its blue-gray disk is best seen around midnight in Aquarius. Help for finding both Uranus and Neptune can be found at the Sky & Telescope magazine’s website.

September events

1 Sunrise, 5:57 a.m.; sunset, 7:13 p.m. New moon, 5:03 a.m.

2 The thin crescent moon is nestled near Jupiter at sunset with Venus to their upper left.

6 The moon is at apogee or farthest distance from Earth.

8 The moon passes above the trio of Antares, Mars and Saturn with the moon being directly above Saturn.

9 First quarter moon, 7:49 p.m.

16 The sun enters Virgo on the ecliptic. Full moon, 3:05 p.m. The full moon of September, being the one nearest the fall equinox, is traditionally called the Harvest Moon. It also is known as the Fruit Moon or Corn Moon.

21 Aldebaran is extremely close to the moon for the next two days at dawn.

22 The autumnal or fall equinox, 10:21 a.m. This is the point where the sun crosses the celestial equator and enters the southern hemisphere. The sun enters the sign of Libra on this first day of fall.

23 Look for Mercury low on the eastern horizon before sunrise with the bright star Regulus to the upper right. Last quarter moon, 5:56 p.m.

29 Look to the predawn eastern horizon where Mercury is situated just to the upper left of the very thin crescent moon with Regulus situated far above.

30 Sunrise, 6:31 a.m.; sunset, 6:18 p.m.

Send astronomical queries to Clair Wood at cgmewood@aol.com or care of the Bangor Daily News, Features Desk, P.O. Box 1329, Bangor, Maine 04402.