A rare event is happening this month–one that only happens once every few years–a naked eye nova is visible in the night sky. This is not a supernova, but what is sometimes called a “classical nova”, literally, a “new” star that appears in the sky. But a nova is not a new star, but an old one. It occurs when a white dwarf strips hydrogen gas from a companion star an accretes it onto its surface. After a while, the white dwarf’s immense gravity compresses the hydrogen enough for fusion to begin explosively, causing a flare many times brighter than even the companion star.
About 40 novae occur in the Milky Way every year, but most of them are not visible to the naked eye. However, there is one that is visible right now. It’s called Nova Delphini 2013, and you can see it clearly if you’re in the Northern Hemisphere. Here’s how:
You may be familiar with the Summer Triangle, three bright stars that appear high in the sky in the northern summer (marked in red): Vega in Lyra, Deneb in Cygnus, and Altair in Aquila. These are probably the easiest features in the sky to spot this time of year.
Look a little below the summer triangle, and you will spot the small constellation of Delphinus, the Dolphin, easily recognized by its compact diamond shape. (Delphinus makes for a pretty nice binocular view on its own.) And if you look a little inside the Triangle, you will see Sagitta, the Arrow. Now follow the line of the Arrow, above the head of the Dolphin, and there you will see a star that isn’t marked on regular star charts (the white spot here). That is an erupting white dwarf called Nova Delphini 2013. Here’s a closer look:
No, it’s not very bright, but it hit a peak magnitude about equal to the stars in Delphinus last week, and it will probably be clearly visible for another week or so. So grab your binoculars, or just walk outside if it’s dark enough, and go take a look.