Sky at a Glance | September 28th, 2012

Dawn view
At dawn this week, watch Regulus approach and pass bright Venus.
Dawn view
Bring binoculars to help pick Regulus out of Venus's glare.
Late evening scenes
The waning gibbous Moon in late evening passes the Pleiades, Aldebaran, and Jupiter. (Moon positions are for North America.)

Friday, Sept. 28

  • Look high in the northeast after dark this week for the landmark autumn constellation Cassiopeia, shaped like a flattened W. It's tilting up to stand almost on end. The brighter side of the W is on top.

  • Uranus is at opposition tonight.

    Saturday, Sept. 29

  • It's Harvest Moon tonight, the full Moon closest to the fall equinox (exactly full at 11:19 p.m. EDT). The Moon shines in dim Pisces this evening, below the Great Square of Pegasus.

    Sunday, Sept. 30

  • Jupiter's Great Red Spot (currently pale orange-tan) should cross Jupiter's central meridian around 12:39 a.m. EDT tonight (9:39 p.m. PDT).

    Monday, Oct. 1

  • Altair is the bright star high in the south at nightfall this week. Look for little Tarazed (Gamma Aquilae) to its upper right, and fainter Beta Aquilae a little farther to its lower left. Altair is just 17 light-years away. It's spinning so fast that it's a flattened ellipsoid, not a sphere.

    Tuesday, Oct. 2

  • As dawn begins to break Wednesday morning, look east for dazzling Venus. Just 0.2° from it or less (as seen from the Americas) is Regulus, less than 1% as bright. You may need binoculars to separate Regulus from Venus's glare. A telescope provides a fine view, though Venus itself is currently an undistinguished gibbous disk just 16 arcseconds in diameter.

    Wednesday, Oct. 3

  • The Pleiades sparkle to the left of the waning gibbous Moon late this evening, as shown at lower right.

    Thursday, Oct. 4

  • Late this evening, look for Aldebaran below the Moon and bright Jupiter to the Moon's lower left, as shown at lower right.

    Friday, Oct. 5

  • Jupiter comes up over the east-northeast horizon around 9:30 or 10 tonight, followed a half hour later by the nearly last-quarter Moon. They rise higher as night grows late, as shown at lower right.

  • Jupiter's satellite Ganymede slowly disappears into eclipse by Jupiter's shadow at 12:32 a.m. EDT tonight a little west of Jupiter, then emerges from eclipse at 2:31 a.m. EDT barely west of the planet's edge. Subtract 3 hours for PDT. A small telescope is all you need.

    Saturday, Oct. 6

  • Vega remains very high in the west after nightfall this week. Look for fainter stars of the little constellation Lyra extending to its left, by roughly a fist-width at arm's length.


    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 guide to 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 the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope effectively.

    You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the classic if dated Burnham's Celestial Handbook.

    Can a computerized telescope replace charts? Not for beginners, I don't think, and certainly not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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."


    This Week's Planet Roundup

    Jupiter on Sept. 13, 2012
    Jupiter's Great Red Spot had recently crossed the planet's central meridian when S&T's Sean Walker took this image on the morning of September 13th. South is up. Note that ring-like Red Spot Junior (Oval BA) is now passing just south of the Great Red Spot with no apparent effect on either of them. Walker used a 12.5-inch Newtonian telescope with a DMK 21AU618 astro video camera.


    See our article Big Breakout on Jupiter on the dramatic growth this year of the North Equatorial Belt (below center here).

    S&T: Sean Walker

    Mercury is hidden deep in the sunset.

    Venus (magnitude –4.1, in Leo) rises in darkness around 4 a.m. daylight saving time (depending on where you live), emerging above the east-northeast horizon two hours before the first glimmer of dawn. By dawn it's blazing high in the east.

    This week Venus is passing Regulus, which is only 1/150 as bright. They're closest on Wednesday morning October 3rd: separated by 0.2° or less before dawn in the Americas. Bring binoculars to help separate them!

    Mars (magnitude +1.2, in Libra) remains low in the southwest in evening twilight. Don't confuse it with twinklier orange Antares ("Anti-Mars") to its left or upper left. The gap between them shrinks from 16° to 11° this week. They're nearly the same brightness.

    Jupiter (magnitude –2.5, in Taurus) rises in the east-northeast around 10 p.m. daylight saving time. Once it's clear of the horizon, look for fainter orange Aldebaran twinkling 8° to its right and Beta Tauri (Elnath) a trace farther to Jupiter's left. By the beginning of dawn, this lineup-of-three stands high and diagonal in the south.

    Saturn (magnitude +0.7) is becoming lost deep in the sunset, far to the lower right of Mars.

    Uranus (magnitude 5.7, at the Pisces-Cetus border) and Neptune (magnitude 7.8, in Aquarius) are up in the southeast during evening. Finder charts for Uranus and Neptune.


    All descriptions that relate to your horizon — 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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