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October: four planets await early birds at dawn. But if you're a night owl instead, you can enjoy the king of the evening sky, Jupiter.

Mainly Morning Planets

Your telescope will find only one planet before midnight this month. Approaching the meridian at nightfall throughout most of October, Jupiter is nicely placed for viewing. The planet glows at magnitude -2.6 and sports a richly detailed disk that spans 44". Your finderscope (or binoculars) will also reveal 4.3-magnitude Iota (t) Capricorni a bit east-southeast of the big planet. Watch in the second half of the month as Jupiter resumes its direct, or eastward, motion among the stars. This will cause it to overtake Iota for the second time in six weeks, passing about 1/3[degrees] north of the star on October 31st and November 1st.

As Jupiter sinks in the southwest around 1 a.m., Mars comes up in the northeast. On the 1st, the 0.8-magnitude planet is in Gemini and forms a shallow triangle with 1.6-magnitude Castor and 1.2-magnitude Pollux. On the 12th, Castor, Pollux, and the Red Planet are arrayed in a 12[degrees]-long line. As Mars enters Cancer that morning, a thick crescent Moon will hang between the planet and the Beehive Cluster, M44. (The Moon and M44 will be separated by less than 3[degrees] over the West Coast at dawn.) During the rest of October, Mars wanders deeper into Cancer. Finally, on the last night of the month, it hovers on the western outskirts of the Beehive Cluster.


Once it clears the treetops, -3.9-magnitude Venus becomes the most brilliant starlike object in the pre-dawn sky. A guest of Leo, on October 1st Venus rises about two hours ahead of the Sun and stands 25[degrees] high at sunrise. However, the Morning Star is slowly losing its dominance as its distance from Earth increases and the planet inches toward its mid-January conjunction with the Sun. By October 31st, Venus will be in Virgo near Spica, rising 90 minutes ahead of the Sun, and standing about 15[degrees] high at sunrise. Its featureless disk will be nearly full and 10" diameter.




Look just below Venus to find Mercury. Now enjoying its best morning apparition of the year, Mercury reaches greatest elongation (18[degrees] west of the Sun) late on the 5th and 6th, when it shines at magnitude -0.4, rises 90 minutes before the Sun, and stands almost 20[degrees] high at sunup. Try to observe Mercury on both mornings. High magnification (and steady seeing) will reveal that its 7"-wide disk is slightly less than 50% illuminated on the 5th, but more than 50% on the 6th. A week later, on the 13th, Mercury will be under 6" across and strongly gibbous-shaped. The planet will be nearing magnitude -1, but will rise just 80 minutes before the Sun and stand only 15[degrees] high at sunrise.

Emerging from the solar glare and below Mercury is Saturn. The planet remains very low in the east all month where turbulent seeing conditions will make detecting its nearly edge-on rings very difficult. On the plus side, Saturn twice plays a part in two planetary pairings this month. The first is on the 8th when -0.7-magnitude Mercury shines about 1/3[degrees] south of 1.1-magnitude Saturn. Then, on the 13th, Venus will blaze slightly more than 1/2[degrees] south of Saturn. Both events will look good in low-power telescopes.

The 8.2-magnitude asteroid Vesta should be identifiable during the predawn hours of the 22nd. That morning it will be about 1/3[degrees] south-southwest of 5.9-magnitude 8 Leonis, which lies 7[degrees] west of 3.5-magnitude Eta ([eta]) in the Sickle of Leo. Careful, though, lest the 8th-magnitude star lurking 13' directly south of 8 Leonis confuses you!

Sampling the October Deep Sky

Large and bright, the co-joined constellations of Andromeda and Pegasus are high in the east at nightfall this month. Here you'll find galaxies aplenty--including the finest spiral in the heavens.

Andromeda and Pegasus are joined together by Alpheratz. Officially Alpha (a) Andromedae, 2.1-magnitude Alpheratz also marks the northeast corner of the Great Square of Pegasus. For our first galaxy, NGC 7331, go westward from Alpheratz past 2.5-magnitude Beta (P) Pegasi, then veer northwestward through 2.9-magnitude Eta (eta) to a pair of 6th-magnitude stars 1[degrees] apart and oriented southwest to northeast. If you nudge your scope 2V3[degrees] north-northeast of 38 Pegasi (the northeastern star in the pair), you should sweep up NGC 7331 in a low-power field.

Only 50 million light-years away, NGC 7331 appears as a narrow, 9.5-magnitude nebulosity oriented north-south. Its dimensions of 10' by 3' give it almost the same proportion as those of the much larger Andromeda Galaxy. I once observed NGC 7331 from a wilderness site using 8-inch and 12 1/2-inch reflectors. At 100x in the 8-inch, the galaxy was a lens-shaped cloud with a bright middle. In the larger scope at 130x the western flank of this fine spiral system was abruptly edged by a dark dust lane. If you have a good sky, try using increased magnification and see if you can pick up a trio of companion galaxies immediately east of NGC 7331. I saw the two brightest companions in the 8-inch scope and all three in the 12 1/2-inch.


At the same pristine site, I went for the notorious Stephan's Quintet, a 1/2[degrees] hop south-southwest of NGC 7331. This mini-cluster comprises five dim galaxies (12.6- to 13.6-magnitude) in an extremely compact grouping less than 4' wide. I glimpsed the brightest member (NGC 7320) in the 8-inch scope, and four of the five in the 12 1/2-inch Resolving the Quintet into five easy pieces requires a large reflector at high power--and a dark sky.

After all these difficult finds, let's try something easier. Andromeda's main attraction is M31, profiled on the next page. But first, for a change of pace, take a moment to admire the binary Gamma ([gamma]) Andromedae, or Almach. Gorgeous Gamma features a 2.3 magnitude yellow-orange sun and a 5.0 magnitude bluish sun 9.7' apart. A 3- or 4-inch scope at about 25x will just split them, and twice that power produces a bright, tight pair. The color contrast is distinct in larger scopes at around 100x.


Early September: 11 p.m.*

Late September: 10 p.m.*

Early October: 9 p.m.*

Late October: Dusk

* Daylight-saving time



Oct 6 Mercury at greatest elongation in the morning sky.

Oct 13 Moon at perigee (229,328 mi).

Oct 21 Orionid meteor shower.

Oct 25 Moon at apogee (251,137 mi).

Oct 3 Full Moon

Oct 11 Last Quarter

Oct 17 New Moon

Oct 25 First Quarter


October Meteors

The Orionid meteor shower peaks early on October 21st. Moonlight will not be a factor since the waxing crescent Moon sets early the previous evening. The shower's radiant, located about 10 [degrees] northeast of 0-magnitude Betelgeuse, crosses the meridian around 5 a.m. Meteor enthusiasts observing at that hour might count 15 or more Orionids per hour in good conditions.


The Andromeda Galaxy

The Andromeda Galaxy, M3I, is a genuine showpiece. It's 2.5 million light-years away, making it both the closest major spiral galaxy, and the most distant object easily visible to the unaided eye. Indeed, M31 glows at magnitude 3.5 and spans an area 3[degrees] by 1 [degrees]. It looms large in binoculars and is satisfyingly detailed in mid-size scopes.

True, little more than the condensed central portion of the galaxy is visible from city backyards; however, viewed under a country sky in a 6-inch instrument, the luminous core grows into a 30'-long elliptical mass enveloping a stellar nucleus. The delicate disk spans at least 2[degrees] oriented northeast-southwest, with the northwestern periphery cut by two parallel dust lanes. Inclined behind a veil of foreground stars, the Andromeda Galaxy is alluring, elegant, and subtly three-dimensional.

Two 8th-magnitude dwarf ellipticals accompany the big galaxy. Just outside of M3 l's disk and due south of the nucleus lies M32. It has dimensions of 8.7' by 6.5' and at high power resembles an unresolved globular cluster with a bright center. Although it looks ordinary next to its colossal parent, M32 outshines most other galaxies in the Messier catalog.


By contrast, nearby M110 is a pale, elongated cloud. Situated beyond the dust lanes northwest of the big galaxy's nucleus, M110 appears much fainter than M32 because its light is spread across an area 22' by 11' in extent. These sibling systems are a challenge for binoculars. In my 7 X 50s, M32 is bright but almost starlike while M110 is big, but very faint.
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Title Annotation:SKY DIARY
Date:Jan 1, 2009
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