A new star has appeared in the sky. Well, not really. It was there all along but it suddenly flared in brightness and caught the attention of an astronomer on August 14th
. Astronomers call it Nova Delphini 2013.
A nova is a stellar outburst but on a less violent scale than a supernova. Unlike a supernova, a nova does not destroy the star.
Novae occur in binary systems where one of the pair of stars is a hot, compact object called a white-dwarf
. The other star in the system (maybe a main sequence
or red giant
star) orbits close enough for material to drawn into an accretion disk around the white dwarf. The material (hydrogen and helium mostly) adds mass to the surface of the white dwarf and increases the temperature and pressure until a runaway nuclear reaction begins. Some of the energy released is in the form of light (the nova in this case brightened by 25,000 times than the progenitor binary system) and intense stellar winds - strong enough to blow away the deposited material so that the reaction eventually grinds to a halt. The flare in brightness is followed by a decay to normality.
The nature of the binary system means that the process may repeat after intervals of decades, centuries or many millennia.
Novae can recur if we wait long enough.
Finding the nova
The nova has the following coordinates:
Right Ascension 20h 23m 30.1s
Declination: +20° 46' 04"
That puts it in a very convenient part of the sky for UK astronomers at this time of the year. Here's a star chart showing the location of the nova in relation to bright stars of the Summer Triangle.
The nova is within the borders of Delphinus (hence the name Nova Delphini 2013) and the borders of Vulpecula and Sagitta. It's probably easiest to locate it visually using Sagitta as a starting point.
I put a couple of green arrows on to show how to star-hop to it from the relatively easy-to-see shape of Sagitta. Follow the shaft of the arrow - it almost points straight to the nova. in binoculars, there are only a couple of stars nearby to rival the nova in brightness.
The nova was about 6th magnitude when it was discovered. That means it was barely visible to the naked eye from darksky site. In a few days it had doubled in brightness and is currently shining at 5th magnitude. That makes it one of the brightest novae of recent years and an easy target for binoculars and small telescopes.
This is the best time of the year to appreciate the crowded starfields of the Milky Way. Until last week Nova Del 2013 was white dwarf lost among the countless millions of stars beyond the reach of all but the biggest amateur telescopes. For now it stands out from the crowd.