Sky at a Glance | September 23rd, 2011

By: Alan MacRobert September 23, 2011 0

Imaging from Puerto Rico with a 12-inch telescope, Efrain Morales Rivera captured the supernova in M101 on August 29th when the outburst was still 12th magnitude. North is to the right.

Efrain Morales Rivera

The M101 supernova is starting to fade. Supernova 2011fe, which erupted in the nearby galaxy M101 a month ago, peaked out at about magnitude 9.9 for a week and is now starting to dim; it was about 10.4 on the evening of September 22nd. See an up-to-date light curve.

You'll almost certainly be using the supernova to find M101, not the other way around; the galaxy (off the handle of the Big Dipper) is diffuse and easily wiped out by any skyglow. To identify which tiny speck is the supernova, use the comparison-star charts that you can generate courtesy of the American Association of Variable Star Observers. Enter the star name SN 2011fe, and choose the "predefined chart scales" A, B, and C. Print out all three. The two brightest stars on the "A" chart are the last two stars in the the Big Dipper's handle.

This is the brightest supernova that's been visible from mid-northern latitudes in three decades. It's well within visual reach of a 4-inch scope. Although it looks like an ordinary star, it's at least 1,000 times more distant than any other star that's visible in amateur telescopes from northern latitudes. See our article The M101 Supernova Shines On.

The waning Moon passes Mars and Regulus in the early hours of the morning.

Sky & Telescope diagram

Friday, Sept. 23

As summer turns to fall, the Sagittarius Teapot moves west of due south right after dark and tips steeply, as if pouring away the last of summer.

The September equinox was at 5:05 a.m. EDT this morning, when the Sun crossed the equator heading south for the season. Fall began in the Northern Hemisphere, spring in the Southern Hemisphere.

Saturday, Sept. 24

Jupiter's Great Red Spot should cross Jupiter's central meridian around 2:02 a.m. Sunday morning EDT; 11:02 p.m. Saturday evening PDT.

Sunday, Sept. 25

Uranus is at opposition tonight: opposite the Sun in the sky. It's in Pisces shining dimly at magnitude 5.7. Use our printable finder chart, or see the September Sky & Telescope, page 53.

About a half hour before sunrise Monday morning, North Americans have an unusually good chance to catch an extremely thin (old) waning crescent Moon. Scan for it with binoculars just above the eastern horizon.

Monday, Sept. 26

With even a small telescope, you can watch Jupiter's moon Io disappear into eclipse by Jupiter's shadow around 12:04 a.m. Tuesday morning Eastern Daylight Time. Io will be barely off the planet's western limb.

Mars is high in the east before the first light of dawn. Use binoculars or a telescope to see the Beehive star cluster far, far behind it. (The 10° scale bar is about the width of your fist held at arm's length.)

Sky & Telescope diagram

Tuesday, Sept. 27

Sometime between about 8:30 and 10 p.m., depending on where you live in your time zone, bright Arcturus low in the west-northwest will sink to exactly the same height as bright Capella has risen to in the northeast. How accurately can you time this event?

New Moon (exact at 7:09 a.m. EDT).

Wednesday, Sept. 28

In bright twilight just 15 minutes after sunset, a telescope may show Saturn less than 2° above much-brighter Venus extremely low in the west. A very thin crescent Moon is setting 12° to their left. Look for Spica twinkling between the planets and the Moon. Good luck.

Thursday, Sept. 29

Jupiter's Great Red Spot (actually pale orange) should cross Jupiter's central meridian around 1:09 a.m. Friday morning Eastern Daylight Time.

Friday, Sept. 30

Once Mars is up in the early-morning hours Saturday morning, Binoculars or a telescope will show that it's passing through the Beehive Star Cluster, M44 in Cancer, as shown above.

Saturday, Oct. 1

In twilight, look southwest for the crescent Moon. Can you see Antares twinkling a few degrees beneath it?

Use binoculars for the faint stars in bright twilight.

Sky & Telescope diagram

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

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 clears off 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 is hidden in the glare of the Sun.

Venus (magnitude –3.9) may be catchable in binoculars just above the due-west horizon a mere 15 minutes after sunset. Good luck. If you detect it, you'll be one of a very select few to pick up Venus this early in its new apparition — compared to the billions of people who will see it as the Evening Star blazing high in twilight in the coming months.

Mars (magnitude +1.3, in Cancer) rises around 2 a.m. daylight saving time. By the beginning of dawn it's in good view high in the east, well below Castor and Pollux. Well to the right of Mars is Procyon. Much farther lower right of Procyon shines bright Sirius. In a telescope, Mars is a tiny blob only 5 arcseconds wide.

Jupiter (magnitude –2.8, in southern Aries) rises in the east-northeast around the end of twilight. 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 early-morning hours, making this the best time to examine it with a telescope. It's a big 48 arcseconds wide.

Io and darker Callisto were just east of Jupiter when S&T's Sean Walker imaged the scene on the morning of September 19th. South is up. Note the reddish Oval BA, "Red Spot Junior," just past the central meridian in the South Temperate Belt. Walker made this stacked-video image with the same telescope and setup as for the Mars image above.

S&T: Sean Walker

Saturn (magnitude +0.8) is disappearing for the season. Use binoculars to search for it low very above the western horizon in bright twilight, to the upper left of brighter but even lower Venus. Venus and Saturn are closing in on each other day by day. Left of Saturn by 7° twinkles Spica.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are well placed in the south and southeast by mid- to late evening. Use our printable finder chart for both, or see the September Sky & Telescope, page 53.

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 from Shop at Sky. Big and lavishly illustrated, it 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. Don’t miss it!

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