The nova that erupted in the Sagittarius Teapot on March 15th reached about magnitude 4.3 by March 21st. As of the morning of the 23rd it was dropping, though still easy in binoculars.
|Update April 1: On the way up again. The last week of amateur observations show the nova struggling back up to shine at about magnitude 4.8, after originally peaking at about 4.3 and declining to 6. Its spectrum has also changed in unexpected ways. See the AAVSO's up-to-date preliminary light curve. See our most recent story.
|Update Sunday March 22: Nova Sagittarii 2015 No.2 reached about magnitude 4.3 yesterday morning and seemed about the same this morning. That's almost 2 magnitudes brighter than at its discovery a week ago. It's now the brightest star inside the main body of the Sagittarius Teapot. It looks definitely yellow to me in 10×50 binoculars. However, after gaining 0.3 magnitude per day from March 16th to the 21st, it looks like it's at a standstill or starting its decline judging by its preliminary AAVSO light curve. This seems to be the brightest nova in Sagittarius since at least 1898, and the brightest anywhere in the sky since Nova Delphini 2013 peaked that August at magnitude 4.3. Sagittarius is a little higher before dawn every morning.|
[Original story, March 16, 2015:]
You never know. On Sunday March 15th, nova hunter John Seach of Chatsworth Island, NSW, Australia, found a new 6th-magnitude star shining in three search images taken by his DSLR patrol camera. The time of the photos was March 15.634 UT. One night earlier, the camera recorded nothing there to a limiting magnitude of 10.5.
A spectrum taken a day after the discovery confirmed that this is a bright classical nova — a white dwarf whose thin surface layer underwent a hydrogen-fusion explosion — of the type rich in ionized iron. The spectrum showed emission lines from debris expanding at about 2,800 km per second.
The nova has been named Nova Sagittarii 2015 No. 2, after receiving the preliminary designation PNV J18365700-2855420. Here's its up-to-date preliminary light curve from the American Association of Variable Star Observers (AAVSO). Here is the AAVSO's list of recent observations.
Although the nova is fairly far south (at declination –28° 55′ 40″, right ascension 18h 36m 56.8s), and although Sagittarius only recently emerged from the glow of sunrise, it's still a good 15° above the horizon just before the beginning of dawn for observers near 40° north latitude. If you're south of there it'll be higher; if you're north it'll be lower. Binoculars are all you'll need.
It looks yellowish. Here's a color image of its spectrum taken March 17th, by Jerome Jooste in South Africa using a Star Analyser spectrograph on an 8-inch reflector. Note the wide, bright emission lines. They're flanked on their short-wavelength ends by blueshifted dark absorption lines: the classic P Cygni profile of a star with a thick, fast-expanding cooler shell or wind.
To find when morning astronomical twilight begins at your location, you can use our online almanac. (If you're on daylight time like most of North America, be sure to check the Daylight-Saving Time box.)
Below is a comparison-star chart from the AAVSO. Stars' visual magnitudes are given to the nearest tenth with the decimal points omitted.
Check back here for further updates!