Northern Rockies Skies for December

November 27, 2012

A monthly look at the night skies of the northern Rocky Mountains, written by astronomers Ron Canterna, University of Wyoming; Jay Norris, Challis, Idaho Observatory; and Daryl Macomb, Boise State University.

Directly overhead in the evening is the very distinctive constellation of Cassiopeia. This "W"-shaped constellation, which never sets below the horizon at our latitudes, represents the “Lady in the Chair” or the “Queen of Ethiopia.”

East of Cassiopeia lies Perseus, the champion. This term comes from his saving Andromeda from a sea monster by using the severed head of Medusa.

Further east, we find a small grouping of stars in Taurus (the bull), called the Pleiades. The "seven sisters" is a relatively young star cluster that actually contains more than 1,000 stars. Look for Sirius, the brightest star in the sky, on the southeast horizon late in the evening.

For you planet watchers, Jupiter is perfect for viewing most of the early evening. It is in Taurus. Saturn rises about two hours before sunrise. The Geminid meteor shower peaks around Dec. 13-14. Since the moon is new, this will be a great time to experience this shower.

The winter solstice is Dec. 21 this year.

Astronomical Instruments: Antikythera Mechanism -- Discovery and Provenience
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Inventions that improve measurement precision of physical phenomena give rise to progress in our understanding, and decisively signal the marks in history that are clear advances of civilization. While new devices are a dime a dozen nowadays, not many centuries have passed since progress only crawled. One instrument -- found in a ship wreck in 60-meter deep water in 1900-1901 near the island of Antikythera, located between Crete and Peloponnesus -- marked an incredible advance in astronomical timing.

Ceramics and coin found with the wreck dated to around 85-60 B.C. A comment by the Greek writer Lucian indicates that the wreck may have been part of a convoy in 86 B.C. carrying loot for the Roman general Sulla from Athens to Italy. Discovered by sponge divers, the wreck’s debris included a box that housed a partially decayed bronze mechanism consisting of 30 recovered gears in 82 fragments. More gears may have been present in the original device.

The mechanism's instructions are written in Koine (common) Greek of the era. Analysis finally published in 1974 (by Professor D. J. de Solla Price of Yale) of the gears' timing as well as the inscriptions date construction of the mechanism fairly precisely to 87 B.C. From ancient writings, we know that very few instruments of similar complexity existed at that or previous epochs.

What we do know from reconstructions is that the movements of this mechanism illustrate motions of the moon and sun as understood by Hipparchus; and, from Cicero's “De re publica,” that Archimedes may have built two earlier copies of the Antikythera mechanism. No machine approaching its complexity or workmanship surfaces again until the 1400s.

The Antikythera Mechanism is on display at the National Archaeological Museum in Athens, Greece. Reconstructed models can be seen at the American Computer Museum in Bozeman, Mont., and at the Children's Museum of Manhattan in New York.

Next time, we will describe the established lunar and solar workings of the Antikythera mechanism and hypothesized planetary motions of possible missing pieces.

To view this month's sky chart, click here.

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