A new nova in Cassiopeia, discovered on March 18th, is bright enough to see in a small telescope.
By the time I got my first look at around 3h Universal Time on March 20th, it had risen to magnitude 8.0, bright enough to see in 50-mm binoculars. Within a day, Nova Cassiopeiae 2021 received its permanent designation, V1405 Cas.
The new object is located at right ascension 23h 24m 48s, declination +61° 11′ 15″. That’s about 6° northwest of 2nd-magnitude Caph (β Cas) and ½° south of the bright open cluster M52, or if you prefer, ½° east of the Bubble Nebula (NGC 7635). Either way, it’s an easy star-hop from Caph, as shown in the finder chart below. And because Cassiopeia is circumpolar from mid-northern latitudes, the nova is visible all night long. Try to catch it when it’s highest, either right at nightfall or just before dawn.
Classical novae like V1405 Cas are close binary stars comprised of a compact white dwarf and either a main-sequence star like our Sun or a red giant. The dwarf’s powerful gravity siphons hydrogen from its partner into an accretion disk. Material then funnels from the disk to the dwarf’s surface, where it’s compacted and heated to around 10 million Kelvin, hot enough to trigger explosive nuclear fusion. Only a relatively small amount of the stolen hydrogen burns; the majority of the material is blasted into space in a rapidly expanding shell.
Astronomers at the National Astronomical Observatory of Japan measured ejected material moving away from V1405 Cas at 1,600 kilometers per second (3.6 million miles per hour). At that rate you could rocket to the Moon in 4 minutes flat!
Novae are fun to watch. When we look at one in our telescopes we’re seeing the flash of light accompanying the blast — like watching a thermonuclear bomb go off but at a very safe distance. Incredibly, an otherwise faint star can brighten from 50,000 to 100,000 times in a matter of hours. Through it all, the underlying white dwarf survives intact, and soon begins accreting a fresh layer of hydrogen for a future blast.