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The Sky This Week, 2015 October 1 - 20

While we're away, some fun in the pre-dawn sky.
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U.S. Naval Observatory Flagstaff Station
Dome of the 1.55-meter Kaj Strand Astrometric Reflector
and the Navy's highest anchors (elevation 7600 feet)

Your "Sky This Week" correspondent will be off for a couple of weeks pursuing the elusive Aurora Borealis from the rugged coastline of Norway. We will resume our weekly updates upon return.

October starts with a waning Moon illuminating the morning sky with Last Quarter occurring on the 4th at 5:02 pm Eastern Daylight Time. New Moon occurs on the 12th at 8:06 pm. Luna will return to the evening sky shortly thereafter, waxing to First Quarter on the 20th at 4:31 pm. The best photo opportunities that find the Moon near bright objects will occur in the pre-dawn skies between the dates of the 8th and the 10th as Luna passes through the gathering of the planets Venus, Mars, and Jupiter in the hour before sunrise. When the Moon returns to the evening sky you can find her about four degrees northeast of fading Saturn in the twilight on the 16th.

The October star-counting campaign for the Globe at Night citizen-science program takes place between the 3rd and the 12th. So far this year over 19,000 people have contributed observations of the visibility of stars in their communities to this effort, which serves to document the growing problem of urban light pollution. This month the target constellation is Pegasus, one of the signature constellations of the fall. Pegasus is easily found in the eastern sky by 9:00 pm, characterized by a large square of second-magnitude stars. The square crosses the meridian between 11:00 pm and midnight and should be easily visible from any location in the northern hemisphere. How many stars can you see within its bounds?

Saturn continues to slips toward the Sun during evening twilight over the next couple of weeks. Unless you have a flat southwest horizon you’ll have difficulty tracking the ringed planet down. However, you’ll at least have the crescent Moon to help you out on the 16th. By the end of the month Saturn will set at the end of evening twilight, and by the end of November he’ll be gone until next spring.

With sunrise now occurring after 7:00 am you can take advantage of the busy bevy of planets that now inhabit the morning sky. Venus, Mars, and Jupiter are all grouped in the constellation of Leo, the Lion, and over the course of the next few weeks will seem to play a game of celestial "leap frog" with the Moon passing through the mix between the 8th and the 10th. Brilliant Venus will drift just over two degrees south of the bright star Regulus on the evenings of the 8th and 9th, then set her sights on cream-tinted Jupiter. Between Venus and Jupiter you should see the more subtle ruddy glow of Mars, which will close in on Jupiter, passing half a degree north of the giant planet on the mornings of the 17th and 18th.

If you have a clear view to the east, look for fleet Mercury a few degrees above the horizon between the 8th and the 16th. He will gradually brighten during this time-span, and if you’re really lucky you might catch a glimpse of the thin sliver of the waning crescent Moon just over a degree to the right of Mercury as twilight gathers on the morning of the 11th.

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