Building may be ancient astronomy lab Arizona structure has sight lines for moon, sun cycles

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Sacred monuments

In the desert of southern Arizona stands a mysterious four-story building built by the Hohokam people. The Hohokam, “those who have gone,” arrived in the region about 300 B.C. and disappeared with almost no trace around A.D. 1400.

The building was enormous for the time, having a base of 40 feet by 60 feet and standing 35 feet high. The frame required more than 600 beams made from fir and pine. Its purpose is unknown, but the top floor, consisting of one single room, may offer a clue. There are two major apertures, one giving a sight line to the extreme setting of the moon during its 18.6-year cycle and the other to the midsummer sunset.

Minor openings point to various sun and moon appearances. It may have been an astronomical laboratory or, according to anthropologist David Wilcox, it was designed for religious purposes having to do with the planting and harvesting of the corn crop. Again the ancients have taken their secrets with them, leaving us only a few tantalizing clues to ponder.

Focus on the planets

There are no naked-eye planets in the evening sky this month, but there will be a total eclipse of the moon on the night of Oct. 27.

Mercury is lost in the sun’s glare for most of October. You might be able to spot it very low in the southeast about an hour before sunrise on or near the last day of the month.

Venus rises in the east about three hours before the sun as the month opens and is the brightest object in the night sky except the moon. In early October an added attraction for planet watchers is the extremely close pairing of Venus with Regulus.

Mars will not make an appearance until the last week of October, when it may be spotted low in the east-southeast about 45 minutes before sunrise.

Jupiter rises in the east during the predawn hours in early October and might be spotted to the lower left of much brighter Venus. Watch the gradual closing of the gap between the two planets as the month progresses.

Saturn rises in the east-northeast about an hour after midnight as the month opens, where it can be found in a line with Castor and Pollux of Gemini. Planet watchers who like to keep an eye on Saturn’s moons will have an added incentive this month in the knowledge that the Cassini spacecraft will be making a close flyby of the largest moon, Titan, on Oct. 26.

Uranus is in the south among the stars of Aquarius shortly after twilight, where it may be seen as a tiny blue-green disk.

Neptune is just to the west of Uranus among the stars of Capricornus where it is revealed as a bluish disk. Both Uranus and Neptune will require powerful binoculars or a telescope to spot.

October events

1 Sunrise, 6:33 a.m.; sunset, 6:17 p.m.

3 Venus is very close, less than 0.2 degree, from Regulus before dawn.

5 The moon is at apogee, or greatest distance from Earth, today.

6 Moon in last quarter, 6:12 a.m.

7 The “star” to the lower right of the moon during the predawn hours is Saturn. Directly above the moon are Castor and Pollux.

8 The Draconid meteor shower peaks tonight, but viewers are told to expect anywhere from none to only a few slow-moving meteor sightings.

10 Look for the waning crescent moon on the eastern horizon about an hour before dawn. Brilliant Venus is directly beneath and Jupiter may be seen just appearing above the horizon. To the moon’s upper right is Regulus.

14 New moon, 12:47 p.m.

16 Look to the southwest horizon about an hour after sunset for orange Antares of Scorpius situated slightly to the upper left of the waxing crescent moon.

17 Moon at perigee, or closest approach to Earth, today.

20 Moon in first quarter, 5:59 p.m.

21 The Orionid meteor shower, spawned by debris from Comet Halley, peaks around this date. Predictions are for 15 to 20 bright, fast-moving meteors per hour.

23 The sun enters the astrological sign of Scorpio, but astronomically is still in Virgo.

27 Full moon, 11:06 p.m. The full moon of October, being the next full moon after the Harvest Moon, is the Hunter’s Moon. There will be a total eclipse of the moon tonight beginning at 9:14 p.m., totality begins at 10:23 p.m. and ends at 11:45 p.m., and the eclipse comes to an end at 12:54 a.m.

30 The sun enters Libra on the ecliptic.

31 Venus and Jupiter are close together on the eastern horizon about an hour before sunrise. This is Halloween, a cross-quarter day marking the midpoint between the fall equinox and winter solstice. Remember, this is the last Sunday in October and you need to set your clocks back an hour as the nation goes from daylight-saving time to standard time. Sunrise, 6:12 a.m.; sunset, 4:26 p.m.

Clair Wood taught physics and chemistry for more than a decade at Eastern Maine Technical College in Bangor.