Sky at a Glance | September 8th, 2011

Supernova in M101, August 22-24
Supernova 2011fe brightens from nothing in these early images taken with the 48-inch (1.2-m) Schmidt telescope at Palomar Observatory on the evenings of August 22, 23, and 24, 2011.

M101 supernova at its peak! The Type Ia supernova discovered in the nearby galaxy M101 on August 24th has leveled off at magnitude 10.0 — just as predicted for a Type Ia supernova at M101's distance. See up-to-date light curve from the beginning. Judge its brightness yourself using the comparison-star charts you can generate courtesy of the American Association of Variable Star Observers (AAVSO). (Enter star name SN 2011fe) .

This is the brightest supernova that's been visible from mid-northern latitudes in decades. It's well within visual reach in a 3- or 4-inch scope. You'll be using the supernova to find the galaxy, not the other way around — especially with the moonlight in the sky this week. The galaxy (off the handle of the Big Dipper) is diffuse and easily wiped out by skyglow. And it's getting lower now; look right after dark. A window of moonless observing time starts opening up again right after dark on September 16th or 17th. See our article, Supernova Erupts in M101.


Friday, Sept. 9

  • The two brightest stars after dark are icy white Vega, now just west of the zenith (if you live in the mid-northern latitudes), and Arcturus, pale yellow-orange, shining ever lower in the west. A third of the way down from Vega to Arcturus is the Keystone of Hercules. Two-thirds of the way down, look for the semicircle of Corona Borealis, the Northern Crown.

    Saturday, Sept. 10

  • Jupiter's inner moon Io disappears into eclipse by Jupiter's shadow around 1:47 a.m. Sunday morning Eastern Daylight Time; 10:47 p.m. Saturday evening PDT. You can watch this happening with a small telescope. For a listing of all of Jupiter's satellite events and Red Spot transits this month, good worldwide, see "Action at Jupiter" in the September Sky & Telescope, page 54.

    Sunday, Sept. 11

  • Full Harvest Moon tonight (exact at 5:27 a.m. Monday morning EDT). The Great Square of Pegasus is off to the Moon's left early in the evening.

    Monday, Sept. 12

  • Jupiter's Great Red Spot transits the planet's central meridian around 2:10 a.m. Tuesday morning EDT; 11:10 p.m. Monday evening PDT.

    Tuesday, Sept. 13

  • Ceres, the largest asteroid, is at opposition this week: magnitude 7.6 and located at the Cetus-Aquarius border. Vesta, the brightest asteroid — and now host to NASA's Dawn spacecraft — is well past opposition, magnitude 6.6 in Capricornus. Use the finder charts in the August Sky & Telescope, page 53, or our Vesta and Ceres finder charts online.

    Wednesday, Sept. 14

  • Before dawn Thursday morning, Mars lies on a straight line with Castor and Pollux, to their lower right. Compare Mars's yellow-orange tint to that of Pollux. Which is deeper?

    Thursday, Sept. 15

  • Look for Jupiter below the waning gibbous Moon this evening. Although they look close together, Jupiter is 1,560 times farther away — and 40 times wider in diameter!

    Friday, Sept. 16

  • This evening, Jupiter shines to the right of the waning gibbous Moon once they rise.

    Saturday, Sept. 17

  • By 10 or 11 p.m. the Big Dipper has swung around to lie level low in the north-northwest. The farther south you are, the lower it will be. If you're in Miami it'll be partly below the horizon.


    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
    must have a detailed, large-scale sky atlas (set of charts). The standards are the Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger and deeper Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts effectively.

    You'll also want a good deep-sky guidebook, such as Sue French's new Deep-Sky Wonders collection, 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 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."


    This Week's Planet Roundup

    Mars on Sept. 13, 2011
    With a diameter of only 4.9 arcseconds, Mars certainly isn't much to look at in a telescope by eye. But stacked-video imaging can work magic. On the morning of September 13th, Sky & Telescope's imaging editor Sean Walker assembled this shot using a 12.5-inch Newtonian reflector at f/44, a DMK 21AU618.AS video camera, and Astrodon RGB filters.

    South is up; note the north polar cloud hood at bottom. The brighter, sharper North Polar Cap should be emerging into view as the cloud hood retreats in coming weeks. The large, darkest diagonal mark near top is Mare Cimmerium. Near the center of the disk, bright Elysium is surrounded by dark features

    S&T: Sean Walker

    Mercury, bright at about magnitude –1.0, is dropping down from a good dawn apparition. Look for it low in the east about 45 minutes before sunrise. It's far below or lower left of Mars, Castor, and Pollux. Mercury passed fainter Regulus on Friday morning the 9th; look now for Regulus rapidly moving off to Mercury's upper right. Binoculars help.

    To find your local time of sunrise, you can use our online almanac for your location. If you're on daylight saving time make sure the Daylight Saving Time box is checked.

    Venus is hidden deep in the glow of sunset.

    Mars (magnitude +1.4, crossing Gemini) rises around 2 a.m. daylight saving time. By the beginning of dawn it's in good view well up in the east, to the lower right of Castor and Pollux. Farther right of Mars is Procyon. Much farther lower right of Procyon shines bright Sirius. In a telescope, Mars is a tiny blob only 4.8 arcseconds wide.

    Jupiter on Sept. 13, 2011
    On a side of Jupiter away from the Great Red Spot, two large dark-red ovals inhabit the north edge of the North Equatorial Belt. Christopher Go took this image on September 13th at 18:06 UT, when the System II longitude on the central meridian was 246°. South is up.

    Jupiter (magnitude –2.7, in southern Aries) rises in the east-northeast around 9 p.m. daylight saving time, not long after dark. Look above it for the stars of Aries and (once Jupiter is well up) closer below it for the head of Cetus, rather dim. Jupiter shines highest in the south in the hours before dawn, making this the best time to examine it with a telescope. It's 46 arcseconds wide.

    Saturn (magnitude +0.9) is disappearing for the season. Use binoculars to search for it low above the western horizon in bright twilight after sunset. It's far below Arcturus and perhaps a bit left. Left of Saturn by 9° twinkles Spica.

    Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are well placed in the south and southeast by late evening. Use our printable finder chart for both.


    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.


    NEW BOOK: Sue French's DEEP-SKY WONDERS! This big, long-awaited observing guide by Sky & Telescope's own Sue French is now available for pre-order from Shop at Sky. This lavishly illustrated book contains Sue’s 100 favorite sky tours (25 per season), with finder charts, from her 11 years of writing the Celestial Sampler and Deep-Sky Wonders columns for S&T. Pre-order now and your book will ship on September 26th. Don’t miss it.


    To be sure to get the current Sky at a Glance, bookmark this URL:
    http://SkyandTelescope.com/observing/ataglance?1=1

    If pictures fail to load, refresh the page. If they still fail to load, change the 1 at the end of the URL to any other character and try again.