Some daily events in the changing sky for October 2 – 10.

This week, keep watch on Mercury and Saturn at dawn as they draw together. They reach conjunction on Thursday morning, as shown here. Bring binoculars; this scene exaggerates their visibility in bright twilight.

Sky & Telescope diagram

Friday, October 2

  • Look upper left of the bright Moon this evening for the Great Square of Pegasus, balancing on one corner. Your fist at arm's length will fit inside it. Binoculars show that the Moon itself is skimming the lower edge of the smaller Circlet of Pisces (during evening for North America). The Circlet is 6° in diameter, about as wide as a typical binocular's field of view.

    Saturday, Oct. 3

  • Full Harvest Moon tonight (exact at 2:10 a.m. Sunday morning Eastern Daylight Time). The Harvest Moon is defined as the full Moon closest to the autumnal equinox.
  • Jupiter's Great Red Spot should cross Jupiter's central meridian (the imaginary line down the center of the planet's disk from pole to pole) around 10:25 p.m. Eastern Daylight Time. The "red" spot appears very pale orange-tan. It should be visible for about an hour before and after in a good 4-inch telescope if the atmospheric seeing is sharp and steady. A light blue or green filter helps. The Red Spot transits about every 9 hours 56 minutes; for all of the Red Spot's central-meridian crossing times, good worldwide, use our Red Spot calculator or print out our list for the rest of 2009.

    Sunday, October 4

  • Jupiter's moon Io reappears from eclipse out of Jupiter's shadow around 11:07 p.m. EDT. A small telescope will show it swelling into view just east of the planet. (For a listing of all such events among Jupiter's moons this month, visible worldwide, see the October Sky & Telescope, page 58.)

    NGC 6934 in Delphinus is a surprisingly nice sight in medium to large telescopes, though you'll never see it as well resolved as in this Hubble Space Telescope view. For its full splendor, see the larger versions.

    NASA / STScI / Wikisky

    Monday, October 5

  • Quick: what's the brightest globular cluster in the northern sky without an M number? Hint: have you ever examined the deep-sky sights around Delphinus, now high in the evening? Take a telescopic tour of this area with Sue French's "Deep-Sky Wonders" column and chart in the October Sky & Telescope, page 61.
  • Jupiter's Red Spot transits Jupiter's central meridian tonight around 12:04 a.m. EDT; 9:04 p.m. PDT.

    Tuesday, October 6

  • Mercury is at greatest elongation, 18° west of the Sun (low above the eastern horizon at dawn).
  • Among Jupiter's moons, Io occults Europa tonight: from 11:35 to 11:41 Pacific Daylight Time, when Jupiter will be getting low in the west even for West Coast observers. (For a complete list of such mutual events among Jupiter's satellites that are visible from North America through the end of the year, see the October Sky & Telescope, page 56.)
  • Before dawn on Wednesday morning, writes our correspondent David Likuski, "Mars helps form a smooth arc with four stars." From upper left to lower right, they go Castor, Pollux, Mars, Procyon, and Sirius. "The apparent magnitudes increase with each step: Castor is the dimmest (+1.6), Sirius the brightest (–1.5). Mars, seen between Pollux (+1.1) and Procyon (+0.4), falls in the middle magnitude-wise as well, at +0.7."

    Wednesday, October 7

  • As dawn brightens tomorrow morning, use binoculars to look for Mercury and Saturn in conjunction just 1/3° apart. They're below Venus in the east, as illustrated below. (To find your local sunrise time, put your location into our online almanac. If you're on daylight saving time like most of North America, make sure the Daylight Saving Time box is checked.)

    Thursday, October 8

  • Jupiter's Red Spot transits Jupiter's central meridian around 9:34 p.m. EDT.

    LCROSS on final approach

    Artist's rendition of LCROSS and its Centaur rocket preparing to hit the Moon.


  • Early Friday morning, at around 4:31:30 a.m. Pacific Daylight Time, the LCROSS spacecraft and its upper-stage rocket will crash into the crater Cabeus near the south pole of the waning gibbous Moon. The Moon will be up in a dark sky for western North America and Hawaii. You may or may not be able to see or record anything with a 10-inch or larger telescope.

    On September 29th, NASA announced that "based on new analysis of available lunar data, [mission control] has shifted the target crater from Cabeus A to Cabeus (proper).... During the last days of the mission, the LCROSS team will continue to refine the exact point of impact within Cabeus crater to avoid rough spots, and to maximize solar illumination of the debris plume and Earth observations."

    See the October Sky & Telescope, page 53, our online followup, and especially our most recent update. Check the LCROSS site for the exact times and other final updates.

    Amateurs planning on watching for the event have set up a Google Group. See also NASA's tips on when and how to watch, including a list of events open to the public. Or watch the coverage on NASA TV beginning at 6:30 a.m. Eastern Daylight Time, about an hour in advance of the impacts. The San Francisco Exploratorium will provide a live webcast from Lick Observatory.

    Friday, October 9

  • There's a growing chill to the October evenings, at least in New England where I live, and by midevening the eastern sky holds harbingers of the winter constellations to come. By 9 or 10 p.m. Capella sparkles in the northeast. To its right, at about the same height in the east-northeast, the Pleiades are coming into view.

    Saturday, October 10

  • Jupiter's Red Spot should transit around 11:13 p.m. EDT.

    Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    Sky Atlas 2000.0 (the color Deluxe Edition is shown here) plots 81,312 stars to magnitude 8.5. That includes most of the stars that you can see in a good finderscope, and typically one or two stars that will fall within a 50× telescope's field of view wherever you point. About 2,700 deep-sky objects to hunt are plotted among the stars.

    Alan MacRobert

    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts; the standards are Sky Atlas 2000.0 or the smaller Pocket Sky Atlas) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion by Strong and Sinnott, the more detailed and descriptive Night Sky Observer's Guide by Kepple and Sanner, or the classic Burnham's Celestial Handbook). Read how to use them effectively.

    Can a computerized telescope take their place? I don't think so — not for beginners, anyway (and especially not on mounts that are less than top-quality mechanically). As Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand and a curious mind." Without these, "the sky never becomes a friendly place."

    More beginners' tips: "How to Start Right in Astronomy".

    This Week's Planet Roundup

    Mercury and Saturn are low in the sunrise due east, below landmark Venus. On the morning of October 3rd they're still 4° apart, with Mercury above fainter Saturn. On the morning of the 8th they come to conjunction just 1/3° apart, as shown at right. On that morning Mercury is magnitude –0.8, and Saturn is a forlorn magnitude +1.1. Thereafter Saturn climbs higher each day, while Mercury and Venus hold at about the same altitudes above the horizon. Binoculars will help.

    Venus (magnitude –3.9, in Leo) shines due east before and during dawn. Look for Mercury and Saturn below it. Regulus is high to Venus's upper right, by an increasing amount each day.

    Mars (magnitude +0.7, in Gemini near Pollux and Castor) rises around midnight or 1 a.m. and is very high in the east before dawn. In a telescope it's still only 6.8 arcseconds wide: a tiny, fuzzy blob, though noticeably gibbous. Mars is on its way to an unremarkable opposition late next January, when it will be 14 arcseconds wide.

    Jupiter (magnitude –2.6, in Capricornus) shines in the southeast as twilight fades — the first "star" to appear after sunset. It's highest in the south by 9 p.m.

    Jupiter on the evening of Sept. 2, 2009

    This year, Jupiter's Great Red Spot has been nicely bordered by the thick white line of the Red Spot Hollow, which indents the dark South Equatorial Belt. Note the very dark red barge following behind the pale Red Spot. The North Equatorial Belt is full of turbulence, including a big blue plume. Far to the right (celestial east), Ganymede and Europa are in conjunction. S&T's Sean Walker took this image at 1:15 UT September 3, 2009. South is up. Stacked-video images like this show much more detail than you're ever likely to see visually on Jupiter.

    For all of the Red Spot's central-meridian crossing times, good worldwide, use our Red Spot calculator, or print out our list for the rest of 2009.

    S&T: Sean Walker

    Uranus (magnitude 5.7, below the Circlet of Pisces) is well up in the southeast during evening. Also catch the 8th-magnitude asteroid 3 Juno in Uranus's vicinity.

    Neptune (magnitude 7.8, in Capricornus) is 7° east of Jupiter.

    See our finder charts for Uranus and Neptune. For a guide to hunting the challenging satellites of Uranus and Neptune at any date and time (you'll need a fairly big scope), see the October Sky & Telescope, page 59.

    Pluto (14th magnitude, in northwestern Sagittarius) is getting low in the southwest after dark.

    All descriptions that relate to your horizon or zenith — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.

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