Let's start by learning to pronounce Ophiuchus — o-fee-YOU-cuss. And the explosion happened to RS Ophiuchi (o-fee-YOU-kee). Its odd name, beginning with two letters of the alphabet, tells us that RS Oph is a variable star. Unlike the steady sun, its light varies or changes, sometimes radically. For long periods of time, RS Oph glows faintly around magnitude 11-12. To see it you need a 4-inch or larger telescope.
But on Sunday, August 8, it suffered an explosion and now shines at magnitude 4.5! While 4.5 isn't BRIGHT bright, it's just bright enough to see faintly from the outer suburbs and countryside without optical aid. With binoculars it's super-easy.
RS Oph is what astronomers call a recurrent nova. All novae involve two stars: a tiny, super-dense white dwarf in close orbit around a normal, sun-like star. As the normal star ages, it loses material to space which the white dwarf grabs and spins into a disk around itself resembling a whirling hula-hoop. Some of that material, composed of mostly hydrogen gas, funnels down to the dwarf's surface, where it's compressed and heated by the star's powerful gravity.
When the bottommost layer reaches a temperature around 18 million degrees Fahrenheit (10 million C), it ignites in a brilliant thermonuclear flash that blows all the accumulated gas into space at thousands of miles a second.
This flash / explosion is a nova, a word that means "new star." As you guessed, it's a misnomer because the star system has been there for billions of years. It only looks new to us because it was too faint to notice before the explosion.
Novae are thought to repeat-outburst every 1,000 to 100,000 years. But a tiny handful of these binary systems, the recurrent novae, explode every 10 to 100 years. RS Oph last lost its cool in February 2006 and before that in January 1985. I was lucky enough to see both blasts. A recurrent nova also differs from a classical nova because the white dwarf's companion is a big gasbag of a thing called a red giant star.
I'm hoping you'll use the maps here to go outside and take a look at the earliest opportunity. RS Oph will remain extra bright for probably about a week before it begins to fade. Expect it to return to its "faint state" in about six weeks. If you have any difficulty spotting the nova or any other questions, please look me up on Facebook and ask for help.
The first person to report the explosion was Irish amateur Keith Geary. He captured it with a time exposure on his DLSR camera and confirmed it in binoculars. Alexandre Amorim of Brazil, another variable star observer, spotted it 25 minutes earlier. Telescope users will soon notice that the star's color will turn red or orange from light emitted by hot hydrogen gas. It's an amazing sight to see.
I can't wait to spot the nova tonight while it's still naked-eye bright. Wishing you clear skies ahead!
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.