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Photo of the Week.. Mountains over the horizon cast shadows into the twilight air from an already set Sun, yielding a "sunburst" effect. The shadows and the intervening sunrays are really parallel; their convergence is an effect of perspective. Courtesy of Lanie Dickel.

Astronomy news for the week starting Friday, October 19, 2012.

Our Moon waxes through the later stages of its crescent phase the early part of the week, then passes through first quarter the evening of Sunday, October 21, as it closes in on setting in North America. The remainder of the week sees it in its waxing gibbous phase as it heads towards full next week, on Monday the 29th. As the Moon swings through Sagittarius and northward against the dim stars of northern Capricornus and southern Aquarius, it highlights the outer bodies of the Solar System, passing Pluto on Saturday the 20th (occulting it as seen from parts of the other side of the world), then rather far north of Neptune on Wednesday the 24th. Neptune is now considered the "last planet," while Pluto is the transition to a dense belt of debris that extends much farther out, the Kuiper Belt's smaller bodies the source of the short-period comets.

The early evening sky is essentially devoid of planets. While Mercury approaches its greatest eastern elongation relative to the Sun (passed on Friday the 26th), it still makes a poor showing, setting in bright twilight. Mars is not all that much better. Passing four degrees north its namesake Antares ("like Ares," the Greek version of Mars) the evening of Friday the 19th, it is a difficult sight as it sets just half an hour after twilight's over. It's been doing so since last August and will continue the pacing throughout most of the rest of the year.

The night really belongs to Jupiter. Now rising early, around 8:30 PM Daylight time, the giant of the Solar system (11 times the size of Earth) maintains its stately position in central Taurus to the northeast of Aldebaran and the Hyades. Jupiter then transits the meridian to the south around 4 AM, just before much brighter Venus rises (all well in advance of twilight), the brilliant planet crossing from southern Leo into Virgo well to the southeast of Regulus. Saturn is completely gone, as it passes conjunction with the Sun on Thursday the 25th.

The week celebrates one of the better meteor showers, the Orionids, which will be best seen (maybe as many as one a minute in a dark sky) emanating from the constellation Orion the mornings of Saturday the 20th and Sunday the 21st (and a bit beyond). The shower is produced by the leavings of Halley's Comet.

In mid-evening look high to the east for the stream of stars that comes off of the northeast corner of the Great Square of Pegasus, which makes the most prominent part of Andromeda. To the south of it find the thin triangle of the ancient constellation Triangulum. From our analogous latitude in the southern hemisphere, the modern southern version, Triangulum Australe, is going down in the southwest.
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