A general rule of skygazing is that the farther you look, the less things change. Clouds? Different from one minute to the next. Moon? Phases shifting every night. Planets? You can easily see them move over the course of a week. But stars? Nah, they're usually the same your whole lifetime. Usually.
Schematic view of Nova Delphini: Tendrils of gas from a sunlike star (right) are pulled toward a compact white dwarf star (invisible within the hot disk at left). Hydrogen piles up on the dwarf's surface until it explodes like an H-bomb. (Credit: NASA/CXC/M.Weiss) Right now is one of the exceptions to that rule. Five days ago, amateur astronomer Koichi Itagaki of Yamagata, Japan was the first to report that a previously obscure star in the constellation Delphinus had suddenly skyrocketed in brightness, by a factor of 50,000, give or take. He recognized it as a nova explosion, now officially designated Nova Delphini 2013. If you act fast and have clear, dark skies you can see it for yourself. Nature has even kindly placed it in a convenient location, high in the east at sunset, with an arrow of stars (the small constellation Saggita--literally, "the arrow") pointing right at it. And if you have the bad luck to live near city lights, beside tall buildings, or just under cloudy skies, have no fear: The Internet will let you watch Nova Delphinus, either live or archived, as it slowly fades away back to its former, anonymous self. Initial studies of Nova Delphini indicate that it is quintessential nova explosion. The object responsible for the sudden flare-up is not one star but a pair of them, a sunlike star orbiting very close to a compact stellar cinder known as a white dwarf. The white dwarf is what's left of a more massive star that burned out first, leaving only its collapsed, extremely dense core behind. The dwarf's intense gravity now yanks gas off its companion. That gas, mostly hydrogen and helium, accumulates on the white dwarf's surface. Eventually it grows so hot and dense that the hydrogen undergoes a runaway thermonuclear explosion. The resulting blast is what we see as the nova. Unlike what happens in a far more violent supernova explosion (they're called "super" for a reason), a nova does not destroy either of the stars. Instead things settle down and the whole process begins again, setting up another nova eruption decades to millennia later. In some cases, such as the binary system RS Ophiuchi, the white dwarf flares over and over with semi-regularity. Novae are also much more common than supernovae, occurring roughly 30 or 40 times a year in our galaxy, versus about 2 supernovae per century. But most of those novae are far away and obscured by gas and dust. Nova Delphini is the first one visible to the naked eye since 2007's Nova Scorpii, meaning it must be relatively close (in cosmic terms) and located along a fairly clear line of sight.
Nova Delphini dominates in this color view through a 17" telescope. Your eyes won't quite deliver that kind of view, unfortunately. (Credit: Virtual Telescope Project) Just to temper your expectations: Nova Delphinus is a 5th magnitude object and slowly fading, meaning that it ranks among the dimmer stars visible to the naked eye under optimal conditions. This will not be a blazing beacon of light! Moonlight will also increasingly disrupt the view this week. You'll want a decent sky chart like this one. Fortunately you can use the bright star Altair to get you to the right part of the sky. From there, hop along the arrow of Saggita, just above the little, dipper-shaped constellation Delphinus, until you get to a star that isn't supposed to be there. The Virtual Telescope Project ran a streaming viewing session of the nova on the Web, as did the Slooh online observatory. There are many nice digital image galleries, such as this one from Universe Today. But much better--grab a pair of binoculars to make things easier, find a good viewing spot, summon some patience, and find the thing yourself. It's a cosmic hydrogen bomb, a nuclear firestorm raging across the surface of a dead star the size of the Earth thousands of light years away. How cool is that, being able to see such a thing with your own eyes? Follow me on Twitter: @coreyspowell
