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Jimmy Westlake: Nova Sagittarii bounces back





During the brief darkness provided by Saturday morning’s colorful total eclipse of the moon (inset), Colorado Mountain College astronomer Jimmy Westlake captured this image of a nova in a teapot. The nova is Nova Sagittarii 2015 No. 2, and the teapot is the familiar pattern formed by the stars of the constellation Sagittarius. Nova Sagittarii has regained its original luster and is again visible to the unaided eye low in the southern sky before dawn.

If you missed the “new star” in Sagittarius last month, like I did, when it was at its peak brightness, I have some good news.

After a sudden decline that took the nova to the limit of naked eye visibility, it has slowly and steadily regained its former brilliance to shine once again at a magnitude of 4.5 in our early morning sky. That makes it easily visible in clear dark skies, however the bright waning gibbous moon will hamper the view for the next week. If the nova holds its current brightness or brightens some more, it should be easy to find when the moon gets out of the way in mid-April.

Australian nova hunter John Seach first spotted the exploding star on March 15 at 6th magnitude, just at the limit of naked eye visibility. It reached a peak magnitude of 4.3 on March 21, but then took a nosedive over the next three days and faded back to the limit of visibility. It looked like Nova Sagittarii’s reign as the brightest nova in two years was over. Then, the nova started to brighten again and, as of Sunday morning, was nearly as bright as it was during its first peak.



Novae explosions are thought to require two very different kinds of stars in a tight binary star system: a bloated red giant and a super-compressed white dwarf. The white dwarf’s powerful gravity siphons fresh hydrogen gas off of the red giant until it erupts in a thermonuclear blast that is visible from across the galaxy. The pair can repeat this explosive dance once the system returns to normal.

During Saturday morning’s beautiful total lunar eclipse, the full egg moon slipped into the Earth’s shadow and, for about 15 minutes, dimmed its light enough that the hazy band of the Milky Way appeared and the stars shone brightly.



I took advantage of the eclipse darkness to observe and photograph Nova Sagittarii. I could spot it easily without optical aid, near the center of the “Teapot” asterism of Sagittarius, low in the southern sky. Even with bright moonlight this week, a pair of ordinary binoculars should make spotting the nova easy.

No one can predict what this exploding star will do next. Amateur and professional astronomers all over the world are watching and monitoring Nova Sagittarii every night so that we can learn more about these unusual erupting stars.

You can keep track of the changing light curve of Nova Sagittarii on the Internet at this web site, posted by the American Association of Variable Star Observers (the AAVSO): http://www.aavso.org/lcg/plot?auid=000-BLP-536&starname=PNV+J18365700-2855420&start=2457096.5&stop=2457121.5&obscode=&obscode_symbol=2&obstotals=no&calendar=calendar&forcetics=&grid=on&visual=on&r=on&fainterthan=on&bband=on&v=on&unvalidated=on&pointsize=1&width=800&height=450&mag1=&mag2=&mean=&vmean=

Happy nova watching!

Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy’s astrophotography website at http://www.jwestlake.com.


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