Sky at a Glance | September 2nd, 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. Click here for larger views. As of August 29th, the supernova had become brighter than the galaxy's nucleus in amateur telescopes.

Supernova in M101. The Type Ia supernova in M101 off the Big Dipper's handle seems to have reached its peak. Supernova 2011fe was discovered on August 24th at magnitude 17.2, reached 13.8 on the 25th and 11.6 on the 29th. By then it was easier to see than the galaxy itself in amateur telescopes through suburban light pollution. By the evening of September 7th it was about magnitude 10.0 and almost ceasing to brighten.

Judge its brightness using the comparison-star charts you can generate courtesy of the American Association of Variable Star Observers (AAVSO).

A normal Type Ia supernova at M101's distance, 23 million light-years, would reach magnitude 10.0 at its peak, assuming none of its light is lost to interstellar absorption in M101 itself. It's well within visual reach in a 4-inch scope. You'll be using the supernova to find the galaxy, not the other way around! Especially with moonlight now returning. See our article, Supernova Erupts in M101.


Friday, Sept. 2

  • Wait up till about midnight, and you'll find Jupiter glaring in the east and Capella, one of the brightest stars in the sky, twinkling in the northeast. Find the midpoint between them. A little lower-right from that point is the Pleiades star cluster, risen up into early display.

    Saturday, Sept. 3

  • Low in the southwest as twilight fades, look well to the left of the Moon for orange-red Antares — a summer star on its way out for the year — as shown below.

  • And right next to the Moon, binoculars and telescopes help show 2nd-magnitude Delta Scorpii in Scorpius's head. The Moon occults (covers) Delta Sco as seen from parts of the southern and eastern U.S. Details.

    Medium twilight
    The waxing Moon marches above Scorpius and Sagittarius as they decline at dusk. For clarity, the Moon is shown three times its actual apparent size.

    Sunday, Sept. 4

  • First-quarter Moon (exact at 1:39 p.m. Eastern Daylight Time). Look for Antares and other stars of Scorpius to the Moon's lower right, as shown above.

    Monday, Sept. 5

  • 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 1:24 a.m. Tuesday morning Eastern Daylight Time. The "red" spot is actually pale orange. It's embedded in the south edge of the South Equatorial Belt, and 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 improve contrast on Jupiter.

    Tuesday, Sept. 6

  • Midway between sunset and sunrise this week, the Pointer stars of the Big Dipper are straight down below Polaris and the north celestial pole. Why? Because this is the time of year when the Sun is passing south of the Pointers. If you could see them when they're high in the daytime, you'd see that they're currently pointing backward to the Sun.

    Wednesday, Sept. 7

  • Before dawn, Mars is passing less than 6° south (lower right) of similarly colored Pollux from this morning through Saturday morning. Watch the triangle that Mars forms with Pollux and Castor change shape daily. Mars is midway in brightness between these two stars.

    Dawn view
    Bring binoculars for the Mercury-Regulus pairing. The visibility of objects in the swelling glow of bright dawn is exaggerated here.
  • As dawn grows brighter, look far below or lower left of the Mars-Castor-Pollux triangle to pick up Mercury close to Regulus.

    Thursday, Sept. 8

  • During dawn Friday morning, spot Mercury low in the east about 45 minutes before sunrise. It's bright: magnitude –0.9. Look less than 1° to Mercury's right for sparkly Regulus, one eighth as bright at magnitude +1.4. 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 like most of the U.S. and Canada, make sure the Daylight Saving Time box is checked.)

    Dawn view
    In the last 24 hours, Mercury's rapid motion has brought it up closer to Regulus.

    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 EDT. 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.


    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).

    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
    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

    Mercury is having a good dawn apparition, brightening from magnitude –0.2 to –0.9 this week. Look for it low in the east-northeast about an hour before sunrise. It's far below Mars, Castor, and Pollux.

    (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 in the glare of the Sun.

    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 right or lower right of Castor and Pollux. In a telescope Mars is a tiny blob only 4.7 arcseconds in diameter.

    Jupiter on August 29, 2011
    Christopher Go in the Philippines took this amazing stacked-video shot of Jupiter with a 14-inch telescope on August 29th. The dark-rimmed Great Red Spot is upper left of center. Lower right of center is a very dark red oval in the North Equatorial Belt. South is up.

    Jupiter (magnitude –2.6, in southern Aries) rises in the east-northeast around 10 p.m. daylight saving time. 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 before dawn, making this the best time to examine it with a telescope. It's a big 45 arcseconds wide.

    Saturn (magnitude +0.9) is disappearing into the sunset. Look for it low above the western horizon as twilight fades, far below Arcturus. Left of Saturn by 10° twinkles Spica. Binoculars help.

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

    Pluto (magnitude 14.0, in northern Sagittarius) is in the south-southwest right after dark.


    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 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) 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!


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