Sky at a Glance | October 5th, 2012

11 p.m. on Friday the 5th
The waning Moon is up below Jupiter by 11 p.m. on Friday the 5th.

Friday, October 5

  • Lots of Jupiter happenings late tonight! Jupiter comes up over the east-northeast horizon around 9 or 10 tonight (depending on where you live), followed a half hour later by the nearly last-quarter Moon. They climb the sky together as night grows late, as shown here.

  • Jupiter's satellite Ganymede slowly disappears into eclipse by Jupiter's shadow at 12:32 a.m. EDT tonight, a little west of the planet. It then emerges from eclipse at 2:31 a.m. EDT even closer to the planet's edge, and finally disappears behind the edge at 5:29 a.m. EDT — just as Io is now fading into eclipse! Subtract 3 hours to get PDT. A small telescope will be all you need.

    Before all this, Jupiter's Great Red Spot should cross the planet's central meridian around 11:47 p.m. EDT.

    For all of Jupiter's satellite events and Great Red Spot transits this month, good worldwide, see "Action at Jupiter" in the October Sky & Telescope, page 53.

    Algol Star Map
    Algol (Beta Persei) was the first eclipsing variable star ever discovered. Good comparison stars are Gamma (γ) Andromedae to Algol's west, magnitude 2.1, and Epsilon (ε) Persei to its east, magnitude 2.9. Click for larger view

    Saturday, Oct. 6

  • The bright eclipsing variable star Algol should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 11:32 p.m. EDT (8:32 p.m. PDT). Algol takes several additional hours to fade and to rebrighten. Click on the chart at right.

    Glance up at Algol at any random time, and you have a 1 in 30 chance of catching it at least 1 magnitude fainter than normal.

    Sunday, October 7

  • 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.

  • Jupiter's Great Red Spot should cross the planet's central meridian tonight around 1:25 a.m. EDT.

    Monday, October 8

  • Even as the stars begin to come out in twilight, Cassiopeia is already higher in the northeast now than the sinking Big Dipper is in the northwest. Cassiopeia's broad W pattern is standing on end.

    Tuesday, October 9

  • Algol should be near minimum light for a couple hours centered on 8:21 p.m. EDT (see Saturday above).

    Wednesday, October 10

  • Jupiter's Great Red Spot should cross the planet's central meridian around 10:54 p.m. EDT.

    Dawn view
    Dawn is coming later and later as October advances, making it easier to catch the waning crescent Moon.
  • In early dawn for the next couple mornings, watch the waning crescent Moon passing to the right of Regulus, then Venus, as shown here.

    Thursday, October 11

  • Bright Arcturus is twinkling lower in the western twilight every week, riding off into the sunset for this year. How many more weeks can you follow it down? Well to its right, look for the Big Dipper lying down low.

    Friday, October 12

  • Jupiter's Great Red Spot should cross the planet's central meridian tonight around 12:47 a.m. Saturday morning EDT.

  • Before dawn Saturday morning, along a path from Southern California through central Texas, the faint asteroid 371 Bohemia should occult an 8.9-magnitude star high in the sky near the Beehive Cluster in Cancer. The occultation should last up to 2 seconds. Details and charts.

    Saturday, October 13

  • Now that it's mid-October, Deneb has replaced Vega as the zenith star after dark (for skywatchers at mid-northern latitudes) — and, accordingly, Capricornus is replacing Sagittarius as the most notable constellation low in the south.


    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).

    Pocket Sky Atlas
    The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but that's less than one star in an entire telescopic field of view, on average. By comparison, Sky Atlas 2000.0 plots 81,312 stars to magnitude 8.5, typically one or two stars per telescopic field. Both atlases include many hundreds of deep-sky targets — galaxies, star clusters, and nebulae — to hunt among the stars.
    Sky & Telescope

    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 Oct. 7, 2012
    Jupiter's Great Red Spot had just crossed the planet's central meridian when Jim Phillips in South Carolina took this image on October 7th. South is up. Red Spot Junior (Oval BA), with a small very dark spot just behind it, has finished passing south of the Great Red Spot with no apparent effect on any of them. Below center, the North Tropical Zone has rebrightened to once again separate the tan North Equatorial Belt from the North Temperate Belt. The bright point is Io.
    Jim Phillips

    Mercury is buried 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), coming above the eastern horizon almost two hours before the first glimmer of dawn. By dawn it's shining brightly high in the east.

    Look above or upper right of Venus for Regulus, much fainter. Regulus pulls farther away from it every day.

    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. The gap between them shrinks from 11° to 7° this week. They're nearly the same brightness.

    Jupiter (magnitude –2.6, in Taurus) rises in the east-northeast around 9 or 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 similar distance to Jupiter's left. By dawn this lineup-of-three stands high and almost vertical in the southwest.

    Saturn is lost in the sunset.

    Uranus (magnitude 5.7, at the Pisces-Cetus border) and Neptune (magnitude 7.8, in Aquarius) are in the southeast to south 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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