风景摄影时间:This Week's Sky at a Glance for September 16 – 24

This Week's Sky at a Glance
Some daily events in the changing sky for September 16 – 24
by Alan M. MacRobert
Imagingfrom Puerto Rico with a 12-inch telescope, Efrain Morales Riveracaptured the supernova in M101 on August 29th when the outburst wasstill 12th magnitude. North is to the right.
Efrain Morales Rivera
The M101 supernova is still at its peak. Supernova 2011fe, whicherupted in the nearby galaxy M101 three weeks ago, leveled off at aboutmagnitude 9.9 and remained that bright for a week. It's now showingsigns of starting to fade; see anup-to-date light curve. Judge its brightness yourself using thecomparison-star charts you can generate courtesy of theAmerican Association of Variable Star Observers (AAVSO)(enter star name SN 2011fe, and choose predefined chart scales "A" and"C". The two brightest stars on the "A" chart are the last two the theBig Dipper's handle).
Bright moonlight washed the sky last week, but now (September 16th) awindow of moonless observing time starts opening up right afternightfall.
This is the brightest supernova that's been visible from mid-northernlatitudes in three decades. It's well within visual reach of a 3- or4-inch scope. Although it looks like an ordinary star, it's at least1,000 times more distant than any other star that's visible in amateurtelescopes from northern latitudes.
You'll probably be using the supernova to find M101, not the other wayaround; the galaxy (off the handle of the Big Dipper) is diffuse andeasily wiped out by any skyglow. See our article,The M101 Supernova Shines On.
Friday, Sept. 16
Jupiter shines to the right of the waning gibbous Moon once they rise shortly after dark.
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 the Dipper will be. If you're in Miamiit'll be partly below the horizon.
Sunday, Sept. 18
Jupiter's moon Io castsits tiny black shadow on Jupiter tonight: from 12:50 to 3:00 a.m. Mondaymorning EDT (9:50 p.m. to 12:00 midnight Sunday evening PDT). For alisting of all of Jupiter's satellite events and Red Spot transits thismonth, good worldwide, see "Action at Jupiter" in the SeptemberSky & Telescope, page 54.
Monday, Sept. 19
Cygnus has a reputationfor being poor in deep-sky objects despite its Milky Way richness. Butmaybe that's because you've never tried teasing out the Berkeleyclusters at the center of the Northern Cross. See Sue French's Deep-SkyWonders article, charts, and photos in the SeptemberSky & Telescope, page 56. Plan your observing session for after dinnertime, when Cygnus is at its highest and the Moon isn't yet risen.
Tuesday, Sept. 20
Last-quarter Moon (exactat 9:39 a.m. EDT). The Moon rises around midnight daylight saving time,in the feet of Gemini left of Orion.
Wednesday, Sept. 21
Jupiter's moon Ganymededisappears into eclipse by Jupiter's shadow off the planet's westernlimb early Thursday morning around 3:30 a.m. EDT. Ganymede reappears outof eclipse closer to Jupiter's limb around 5:34 a.m. EDT.
The waning Moon passes Mars and Regulus in the early hours of the morning.
Sky & Telescope diagram
Thursday, Sept. 22
Before dawn tomorrow, lookeast and you can spot Mars upper left of the waning Moon, as shown here.Is this the first time you've seen Mars this year?
Friday, Sept. 23
The September equinoxoccurs at 5:05 a.m. EDT this morning, when the Sun crosses the equatorheading south for the season. Fall begins in the Northern Hemisphere,spring in the Southern Hemisphere.
As summer turns tofall, the Sagittarius Teapot moves west of due south right after darkand tips steeply, as if pouring away the last of summer.
Saturday, Sept. 24
Jupiter's Great Red Spotcrosses the planet's central meridian around 2:02 a.m. Sunday morningEDT (11:02 p.m. Saturday evening PDT).