This Week’s Sky at a Glance

Friday, October 11

  • First-quarter Moon (exact at 7:02 p.m. Eastern Daylight Time). The Moon, half lit, shines above the tilting Sagittarius Teapot in early evening.

  • Triple shadow transit on Jupiter. A rare case of three moons — Io, Europa, and Callisto — casting their tiny black shadows onto Jupiter at once happens late tonight, from 4:32 to 5:37 Universal Time October 12th (12:32 to 1:37 a.m. Saturday morning Eastern Daylight Time). Jupiter will be high and best placed for telescope users in Europe and Africa, and low in the eastern sky for eastern North America. See our article

    Having passed Venus, Antares is finally blinking its low farewell for the year.
  • Algol in Perseus, the prototype eclipsing binary star, should be in one of its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 8:53 p.m. EDT. Algol takes several additional hours to fade and to rebrighten. Here's a comparison-star chart giving the magnitudes of three stars near Algol. Use them to judge its changing brightness.

    Saturday, October 12

  • Venus has been approaching much dimmer Antares, which twinkles to Venus's left in the southwest in evening twilight. They're now 4½° apart. They'll pass 1½° from each other on Wednesday.

    Sunday, October 13

  • The zenith star soon after dark (for skywatchers at mid-northern latitudes) is no longer Vega but Deneb. It will remain there for weeks to come, since night is falling earlier and earlier all the time — counteracting the westward turning of the constellations if you observe at nightfall.

    Monday, October 14

  • Before dawn Tuesday morning, look for orange-yellow Mars just 1° from blue-white Regulus in the eastern sky. They're far lower left of bright, high Jupiter.

    Tuesday, October 15

  • The upper-right edge of the Great Square of Pegasus points down at the Moon this evening.

    Wednesday, October 16

  • Antares twinkles 1½° below Venus as twilight fades.

    Thursday, October 17

  • The bright, nearly full Moon shines below the bottom corner of the Great Square of Pegasus this evening.

    Friday, October 18

  • Full Moon. A slight penumbral eclipse of the Moon will be detectable this evening by careful Moon-watchers in the eastern half of North America. The Moon will be deepest in the pale outer fringe (penumbra) of Earth's shadow around 7:50 p.m. Eastern Daylight Time. Some unusual shading on the Moon's south-southeastern side should be fairly plain to see. Subtler traces of the penumbral shading may be visible for almost an hour before and after that time.

    In Europe and Africa, the penumbral eclipse happens in the middle of the night when the Moon is high: centered on 23:50 Universal Time (GMT).

    Saturday, October 19

  • Look about a fist-width above the Moon this evening for the main stars of little Aries, lined up nearly horizontally.


    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.

    This is an outdoor nature hobby. 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).

    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 once you know your way around, the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

    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 beloved if dated Burnham's Celestial Handbook.

    Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability, which means heavy and expensive). 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

    Mercury (magnitude 0.0) remains deep in the glow of sunset. About 30 minutes after sunset, use binoculars to look for it about 22° to the lower right of Venus. Saturn (magnitude +0.7) glows 7° to Mercury's right or upper right.

    Oval BA. It shows up on all of my videos this morning."" credits="S&T: Sean Walker" width="" height="" align="right"]
    Venus (magnitude –4.4) shines brightly in the southwest during dusk, gradually moving higher week by week. In a telescope it is waning to be hardly more than half lit, and enlarging to be 21 arcseconds tall.

    Mars (magnitude 1.6) rises around 3 a.m. close to Regulus (magnitude 1.4) in Leo. By dawn they're high in the east. They pass 1° apart on the morning of October 15th.

    In a telescope, Mars is still just a tiny blob 4.6 arcseconds wide.

    Comet ISON is also near Mars, but it's still a faint telescopic target at 11th or 10th magnitude. Use the finder chart for it (with respect to Mars and Regulus, among faint stars) in the November Sky & Telescope, page 50.

    Jupiter (magnitude –2.2, in Gemini) rises in the east-northeast around 11 or midnight and blazes high in the south by dawn. About 8° left of Jupiter after it rises are Castor and Pollux.

    Unlike the blank face that Uranus showed during Voyager 2's 1986 flyby, Uranus is now displaying belts and lighter zones — to the unusually capable imagers who can capture them! Damian Peach in England took this shot on October 6th when Uranus was just 3.7 arcseconds wide. He used a 12-inch Schmidt-Cassegrain scope, a deep-red RG610 filter, 35 minutes of video shot at a very slow 3 frames per second due to Uranus's dimess, and software for de-rotating the planet, frame selection, and frame stacking.

    Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are high in the southeast and south, respectively, by 9 or 10 p.m. Finder charts for Uranus and Neptune. See also the October Sky & Telescope, page 50.


    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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