Astronomy From Your Backyard - 9/29 to 10/5 2010
Wednesday, September 29 2010 @ 11:42 am EDT
Contributed by: dgrosvold
By Dave Grosvold
The weather this week will be absolutely perfect for sky-watching, with low humidity providing above-average transparency all week and the temperatures low enough after dark to make it very comfortable.
By Wednesday, the Moon will not rise until 11:03 PM CDT, late enough that the glare will no longer interfere with evening observing. The Moon reaches Last Quarter at 10:53 PM CDT on Thursday evening, though it will not rise until after midnight. Moonrise occurs about an hour later each night.
With the Moon gone from the evening sky, now is the time to start looking for Comet 103P/Hartley (Hartley 2.) Comet Hartley 2 is just now becoming visible, reaching magnitude 5.9 on Wednesday evening. Comet Hartley 2 should brighten to magnitude 5.4 by Tuesday evening. The comet will continue to brighten in magnitude over the next three weeks.
Wednesday evening, 103P/Hartley lies in the north-northeast, in the constellation of Cassiopeia, the Beauty Queen, approximately 0.87 above Zeta Cassiopeiae. Over the course of the week, Comet Hartley 2 will track down to the southwest, as shown in the finder chart. At magnitudes dimmer than 5, you will need binoculars or a small telescope to see Comet Hartley 2 in any but the darkest of skies.
In late evening, as Jupiter rises high in the southeast, look for Fomalhaut, (pronounced FOAM-a-lot, or less commonly, FOAM-al-howt.) Fomalhaut is known as the Autumn Star, sparkling far to Jupiter's lower right in the south-southeast. The name Fomalhaut means "the mouth of the whale" in Arabic, and it is the brightest star in the constellation Piscis Austrinus, the Southern Fish.
Uranus, at magnitude 5.7, is only 1° to 1.5° to the left of Jupiter this week, still close, but you may need to move a few field-of-view widths in a telescope or binoculars to spot it. Neptune is also a relatively easy target early in the evening on the border between Capricornus, the Goat-Horn, and Aquarius, the Water Bearer. Can you see any color in Uranus and/or Neptune? There should be just the tiniest hint of pale green in Uranus and an equally pale blue in Neptune.
Even though Venus is at its brightest now at magnitude –4.8, it is becoming a thin, long crescent. Venus is sinking very low in the southwest during bright twilight, setting well before dark ahead of Mars, 6.5° to Venus's upper right all week. That's about one field-of-view width in a typical pair of 7 x 50 binoculars, which you'll definitely need to spot either of them.
Mercury is still very bright at magnitude -1, and is a fine morning target for planet watchers. Once again this week, look for it low in the east about 45 minutes before sunrise. It sinks lower as the week advances, getting lost in the glare of the sun by mid-next week.
After Venus sets, look to the west-northwest, and notice that five constellations form a line descending from the zenith down to the horizon. Remember from earlier articles that the zenith is the point directly overhead from your observing position. Near the zenith is the bright star Deneb: the head of the Northern Cross asterism, which is actually the tail of Cygnus, the Swan. Next down is Lyra, the Lyre, with the bright star Vega, then comes dim Hercules, the Kneeler, the then little Corona Borealis, the Northern Crown, and finally big Boötes, the Herdsman, with bright reddish Arcturus low in the west-northwest.
Hiding in Hercules is one of the most beautiful jewels of the night sky, the Great Cluster in Hercules (M 13,) the brightest globular cluster in the northern hemisphere. M 13 lies two-thirds of the way along the longest side of the Keystone asterism, a quadrangle in Hercules formed by the stars Pi (π,) Eta(η,) Zeta(ζ,) and Epsilon (ε) Herculis. Look about mid-way up to the zenith in the west-northwest for the Keystone, and then look to the north end of the longest side to find M 13,in a clear dark sky, it should be visible as a fuzzy patch slightly larger than a star. A telescopic view reveals a myriad of stars swarming around in a big ball — about a hundred thousand of them in all. M 13 is a spectacular sight on a crisp clear night like the ones we'll have this week, and should not be missed.