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This Week's Sky at a Glance
Some daily events in the changing sky for September 8 – 17
by Alan M. MacRobert
Supernova2011fe brightens from nothing in these early images taken with the48-inch (1.2-m) Schmidt telescope at Palomar Observatory on the eveningsof August 22, 23, and 24, 2011.Peter Nugent / Palomar Transient FactoryM101 supernova at its peak! The Type Ia supernova discovered inthe nearby galaxy M101 on August 24th is no longer brightening much. Itseems to be leveling off at about magnitude 10.0 — just as predicted fora 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-northernlatitudes in decades. It's well within visual reach in a 3- or 4-inchscope. You'll be using the supernova to find the galaxy, not the otherway around — especially with the increasing moonlight this week. Thegalaxy (off the handle of the Big Dipper) is diffuse and easily wipedout by skyglow. And it's getting lower now; look right after dark. Seeour article, Supernova Erupts in M101.
After this morning, watch Regulus pull away to Mercury's upper right all week.Sky & Telescope diagramThursday, Sept. 8
During dawn Friday morning, spotMercury low in the east about 45 minutes before sunrise. It's bright:magnitude –0.9. Look less than 1° to Mercury's right for sparklyRegulus, one eighth as bright at magnitude +1.4. Binoculars help. (Tofind your local time of sunrise, you can use our online almanacfor your location. If you're on daylight saving time like most of theU.S. and Canada, make sure the Daylight Saving Time box is checked.)Friday, Sept. 9
The two brightest starsafter dark are icy white Vega, now just west of the zenith (if you livein the mid-northern latitudes), and Arcturus, pale yellow-orange,shining ever lower in the west. A third of the way down from Vega toArcturus is the Keystone of Hercules. Two-thirds of the way down, lookfor the semicircle of Corona Borealis, the Northern Crown.Saturday, Sept. 10
Jupiter's inner moon Iodisappears into eclipse by Jupiter's shadow around 1:47 a.m. Sundaymorning Eastern Daylight Time; 10:47 p.m. Saturday evening PDT. You canwatch this happening with a small telescope. For a listing of all ofJupiter's satellite events and Red Spot transits this month, goodworldwide, 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 isoff to the Moon's left early in the evening.Monday, Sept. 12
Jupiter's Great Red Spottransits the planet's central meridian around 2:10 a.m. Tuesday morningEDT; 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 Thursdaymorning, Mars lies on a straight line with Castor and Pollux, to theirlower right. Compare Mars's yellow-orange tint to that of Pollux. Whichis deeper?Thursday, Sept. 15
Look for Jupiter belowthe 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 BigDipper has swung around to lie level low in the north-northwest. Thefarther south you are, the lower it will be. If you're in Miami it'll bepartly below the horizon.
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