On March 18 this year, amateur astronomer Yuji Nakamura of Japan discovered a "new star" in Cassiopeia in pictures he took with a digital camera and 135-mm lens. At the time you needed a small scope to see it, but then the star quickly rose to magnitude 8, bright enough to see faintly in binoculars. Officially named V1405 Cassiopeiae (or simply V1405 Cas), it hovered around that brightness until the past week, when it suddenly vaulted into naked-eye visibility. I figured it was high time to share the news.
While the nova still appears dim without optical aid — magnitude 5.5 as of May 8 — it's super easy to see in any pair of binoculars. It's also located in the familiar W of Cassiopeia, one of the northern circumpolar constellations that circles around the North Star without setting. That means it's in view the entire night. Just before dawn is the best time because the nova is higher up than during the evening hours. But as long as you can find an open view of the northern sky and see Cassiopeia, it's within your reach.
When you hear the word "nova," you might think V1405 Cas is either a brand new star or an old star that blew up, similar to a supernova. Neither is true. A nova is an event that occurs in a pair of closely orbiting stars comprised of a Earth-sized, super-dense white dwarf and a star similar to our sun.
The dwarf’s powerful gravity siphons hydrogen from its partner into a whirling disk of material. Like water going down a bathtub drain, the gas funnel down to the dwarf’s surface, where it’s compacted and heated to millions of degrees, hot enough for nuclear fusion to occur. Just like it does in a thermonuclear bomb, fusion releases gobs of energy, triggering a titanic explosion.
Only a relatively small amount of the stolen hydrogen burns; the majority of the material is blasted into space in a rapidly expanding shell. What was a faint, unassuming star a moment ago can brighten from 50,000 to 100,000 times in a matter of hours. This is what we see when we look at a nova. Through it all, the white dwarf survives intact and starts the whole process again, greedily gathering more hydrogen for a future blast.
Last night (May 8) I spotted the nova without optical aid, which I found thrilling. Naked-eye novae are relatively rare. Of course, it appeared faint. That's why I suggest you find it first in binoculars. Once you know precisely where to look, try to spot the star unassisted. Observe V1405 Cas as often as you can. Novae brighten, fade, and often re-brighten (as this one did), so there's always a potential surprise awaiting each clear night. The maps include the magnitudes of several stars to help you to document the V1405 Cas's changing brightness.
As you do, relish the pleasure of watching one of the biggest bombs in the universe detonate from a safe distance.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.