Can you imagine knowing the stars so well that if a dim one appeared you may have just looked up and noticed one “that shouldn’t be there”?
A naked eye nova appeared in the constellation Delphinus the Dolphin in August. It peaked in brightness on August 14th a little brighter than +4.5 magnitude. It has slowly faded since then, and was roughly magnitude +6 by August 25.
An amateur astronomer in Japan, Koichi Itagaki of Yamagata, discovered the nova on a photograph he took of that region of the sky on August 14. He had just taken another one the night before and the “new” star was not there.
So you know, astronomers calibrate the brightness of stars and other sky objects on a magnitude scale, with +6 roughly the faintest unaided eyes can detect under a typical, dark and clear rural sky. Some eagle-eyed observers under excellent conditions have detected even fainter, +7th magnitude stars. The brightest stars of the night sky are 0 magnitude and even brighter.
Referred to as Nova Delphini 2013, a search of deep star atlases reveal that the star was there before, shining only at magnitude +17 and needing a fairly large telescope to pick out among the thousands of other similarly appearing specks of starlight nearby.
Nova means “new star,” but actually the star was there all along. The star erupted in brightness nearly 10,000 fold. A classic nova occurs in a close binary star system, where a stream of hydrogen from one star is absorbed onto a dense white dwarf star. A runaway hydrogen fusion reaction results, igniting in effect, a massive hydrogen bomb. The brilliant flash then announces to the galaxy, “I am here” and we on Earth look up in amazement.
The Dolphin constellation is one of the favorites of the summer evening sky. Found just east of the bright star Altair and below the cross-shaped constellation Cygnus the Swan, the Dolphin’s main stars form a tight, little box, rather squat, with another star off one corner. Some call it “cute.”
The nova is just north of the box, and east of the small and dim but interesting constellation Sagitta the Arrow. In fact, the “arrow” seems to point right toward the nova.
A detailed star chart is needed to pick it out among other stars. The nova was easily visible in binoculars. All too soon it is expected to fade more, requiring a telescope to track it down.
Keep looking and learning the sky. You never know what may appear. In August 1975 a bright nova appeared in Cygnus the Swan, about magnitude +2, similar to the other principal stars of the Swan’s shape. The nova radically altered the appearance of the constellation.
For more information, including a star chart to locate the nova, see online at www.skyandtelescope.com.
New moon is on Sept. 5.
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Keep looking up!