Japanese observers have spotted a nova, the fourth seen in Sagittarius so far this year. This one is relatively bright and easy to spot from your backyard.
For the fourth time this year, a dim star has erupted into prominence in the constellation Sagittarius, the Archer. Unlike the others, however, none of which got brighter than magnitude 9½, this one has rocketed from anonymous obscurity to magnitude 7.8. That's bright enough to be spotted with relative ease from your backyard.
But don't just go rushing outside — to see it, you'll need to know exactly where to look, both because it's fairly near the horizon (which will make it appear somewhat dimmer) and because it's in a region of sky already crowded with stars along the Milky Way. For those of us at mid-northern latitudes, the best time to look is around midnight. The Moon, now a few days past full, offers only modest interference over in the east.As the chart at right shows, the nova is located between the "lid" and "spout" of the Teapot asterism in Sagittarius. Its coordinates are right ascension 18h 20.5m, declination –27° 44? (equinox 2000.0). This puts it 2¼° north of Delta Sagittarii (Kaus Media), the 3rd-magnitude star marking where the lid and spout connect.
Observers Koichi Nishiyama (Kurume, Japan) and Fujio Kabashima (Miyaki, Japan) spotted the "new star" in images taken late on July 7th with a 105-mm f/4 camera lens attached to a CCD camera. The IAU's Central Bureau for Astronomical Telegrams, which announced the discovery, notes that three other Japanese observers — Hiroshi Kaneda, Hideo Nishimura, and Shizuo Kaneko — independently confirmed the find. Prediscovery images show that the star was no brighter than 13th magnitude in mid-June.
"The Japanese have a solid nova-hunting program in place," notes Arne Henden, director of the American Association of Variable-Star Observers (AAVSO). And even though Sagittarius is low on their horizon too, he adds, to make these discoveries requires "equipment, observing strategy, software and skill, and that is why the Japanese excel."
Roughly three dozen novae occur in our galaxy each year, though it's a bit unusual to have several appear in the same constellation. Unlike last month's stellar outburst in the same general region, it didn't take long to confirm this one as a true nova. Initially the IAU designated the outburst as PNV J18202726-2744263, but quick-look spectra showed that the star's light has many emission lines, including several from ionized iron. So now it's officially Nova Sagittarii 2012 No. 4.Last night, when I first got word of the nova, I took a quick look outside and realized that eyeballing it was not going to happen — unless I wanted to cut down some of my neighbor's trees. So I turned to the next best thing: a remotely operated telescope high in the mountains of New Mexico. This particular one, owned by itelescope.net, was just right for the task. So, just a few minutes and keystrokes later, I'd set up the "observing run" that netted the image seen in the animation at right.
By the way, a great way to be notified about unexpected celestial happenings such as this is to sign up for Sky & Telescope's AstroAlerts. It's a free service that emails you with late-breaking details.