Star Watch: October 2015
In October Saturn drops into the sun's afterglow, but its fate may go unnoticed, given everything the morning planets are up to.
The month begins with three planets and one bright star stacked up in the eastern predawn sky. Look an hour before sunrise to see, from top to bottom, brilliant Venus; Regulus, the heart of Leo, the lion; dim Mars; and Jupiter, bright but no match for Venus.
By Oct. 8, Earth's orbital motion will have pushed Regulus higher than Venus. On that morning, a waning moon hangs above Venus and Regulus, poised for a three-day plunge through the line-up. On Oct. 9 the moon is closest to Mars, on Oct. 10 it appears below Jupiter, and on Oct. 11 a very old sliver of moon, along with Mercury, just make it over the eastern horizon before the sun's rays overpower them.
Regulus keeps climbing, but Venus, Mars and Jupiter spend most of the month drawing closer together. Jupiter climbs past Mars in mid-month, coming closest on Oct. 17 and Oct. 18, then proceeds to Venus, passing about two full moon widths from the queen of planets on Oct. 25 and Oct. 26. Meanwhile, Venus and Mars close in on each other.
As a bonus, the familiar winter stars are up in the south an hour before sunrise, with the brightest of all — Sirius — at about the same altitude as Venus. This makes for a great chance to compare the brightest star and planet.
Even October's full moon steals the limelight from the evening sky. It rises the evening of Oct. 26, about 10 hours after reaching perigee, its closest approach to Earth in a given orbit. The moment of fullness comes at 7:05 a.m. the next morning, barely 23 hours after perigee, so it will appear larger than usual. This full moon is called the hunter's moon, because with the fields empty of crops, American Indians laying in food for the winter could use its light to hunt summer-fattened deer gleaning for grain by night.
But the evening sky does have its attractions, especially during the first two full weeks of the month, when no moon interferes. Try "star hopping" to the Andromeda Galaxy, our Milky Way's closest large neighbor. Starting with the Great Square of Pegasus high in the south-southeast, find the line of stars extending northeast from the Square's upper left corner. From the second star in the string, extend an imaginary line perpendicularly northward, to a nearby but fainter star. Extend the line the same distance again, and you should see a fuzzy oval patch; this is the Andromeda Galaxy. Binoculars are highly recommended.
October ends with Halloween, an old Celtic holiday known as Samhain (rhymes with HOW-when). It was one of four "cross-quarter days" falling midway between an equinox and a solstice. At sunset that night, evil spirits that had been cooped up since May Day were freed to wreak havoc on humankind. People lit candles inside gourds to ward off the spirits and bribed them with gifts of food, two traditions that survive in the lighting of jack o' lanterns and the handouts to trick-or-treaters.
The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. For more information and viewing schedules visit www.d.umn.edu/planet.