A dazzling star explosion discovered in the night sky last week is the brightest nova seen from Earth in at least five years and its visible now to the naked eye.
The Nova Delphinus 2013 star explosion can be seen by the naked eye from places without too much light pollution, skywatching experts say. The stellar phenomenon is expected to be visible for weeks to come, and its location in the night sky should make the nova easy for even novice stargazers to spot.
“The nova is easy to locate north of the lovely star pattern of Delphinus. And the constellation Sagitta, the Arrow, points right toward it,” Tony Flanders, associate editor of Sky & Telescope, said in a statement.
In the last 112 years, 47 novas have brightened into naked-eye view and novas as bright as Nova Delphinus 2013 occur about every 10 years, skywatching experts say. The new nova has also been referred to as Nova Delphini 2013.
Nova Delphinus 2013 was discovered by Koichi Itagaki of Yamagata, Japan, in an image taken on Aug. 14. Itagaki noticed a bright spot that was not present in a photo of the sky that he took the previous day.
Before erupting, the nova was apparently a dull magnitude +17 star on the scale used by astronomers to measure the brightness of night sky objects, in which higher numbers denote dimmer objects. The threshold of what the human eye can see is about magnitude +6.5. The stellar magnitude scale is logarythmic, so an object that differs by ten magnitudes in brightness is actually many thousands of times brighter.
Nova Delphinus 2013 increased in brightness by about 100,000 times when it reached a peak magnitude 4.5 on Aug. 16. Now the nova is holding steady at magnitude 4.9, but its intensity could change.
A typical nova occurs in a binary system where one at least one star is a white dwarf, a tiny, super-dense core of a star. Its companion star sends a stream of hydrogen onto the white dwarf and when that gaseous layer grows thick and dense enough, a runaway hydrogen-fusion reaction is set off.
Unlike in supernovas, white dwarfs survive novae, and the process may repeat in a few years to tens of thousands of years. Supervovas are much rarer than novae (the last one in our galaxy that was visible to the naked eye occurred in 1987). They are also intrinsically much brighter than novae, because they usually involve the destruction of an entire star, and are thought by astrophysicists to be the origin of all the elements that constitute the universe, with the exception of hydrogen, which was created by the Big Bang.