A new nova in Cassiopeia, discovered on March 18th, is bright enough to see in a small telescope.

Nova Cassiopeiae 2021, designated V1405 Cas, shone around magnitude 8 on March 21, 2021. It’s located in a rich region of western Cassiopeia.
Dennis di Cicco / Sean Walker MDW Sky Survey

Like a spring flower, a bright, new nova has bloomed from the dark earth of Cassiopeia. Yuji Nakamura of Japan discovered the object at magnitude 9.6 in four images he took with a 135-mm lens on March 18th. Four days prior, nothing was visible at the location down to magnitude 13.

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 nova is circumpolar for mid-northern latitudes and observable all night, but it’s best seen during the early evening and just before dawn
Stellarium with additions by the author

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.

V1405 Cas is an easy star-hop toward celestial west from second-magnitude Caph (β Cassiopeiae). Use the two outlined triangular asterisms to aid in finding the nova inside a 2.2°-wide circle.
Stellarium with additions by the author

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.

Voyage into the vortex
In this illustration, the star at right is losing matter through its Roche Lobe to the white dwarf (center). Material first flows into a disk and then spirals down to the dwarf’s surface, where it can later detonate in a thermonuclear explosion.
NASA / CXC / M. Weiss

When a new nova comes to light, astronomers try to identify it with a previously known star. V1405 lies just 0.12″ from the W UMa-class (denoted EW) eclipsing-binary star CzeV3217, close enough that the latter appears to be the nova’s progenitor. Like nova systems, W UMa-class stars orbit close enough to transfer material through a common “neck” but with a key difference: Both members are main-sequence stars that burn hydrogen like the Sun, not end-of-the-road white dwarfs.

The nova changed our understanding of the system. According to Patrick Schmeer, with the American Association of Variable Star Observers (AAVSO), the classification of CzeV3217 now has been revised in the AAVSO database from EW to N+E — nova + eclipsing. How’s that for quick work?

This AAVSO chart plots V1405 Cas’s position (the open circle, arrowed) and field stars. Magnitudes are shown with the decimal omitted.

To see the most up-to-date brightness measurements, go to the AAVSO website. Under "Pick a Star," enter "V1405 Cas," and choose "Plot a light curve." (Under "Preferences" you can choose to see calendar dates instead of Julian Days.)

Try to observe V1405 Cas as often as you can. Novae brighten, fade, and often re-brighten, so there’s always an element of surprise. With the AAVSO chart you can estimate the star’s brightness changes and even report them back to the organization. Even a single observation will prove useful to astronomers who use AAVSO data to understand and model V1405 Cas’s behavior.

Novae are exciting to watch not just because things are blowing up but also because you get to witness an essential process that makes the universe tick. Through explosive fusion, novae seed space with carbon, nitrogen, oxygen, and more. For all you know, some of your very own atoms may have originated in a similar catastrophic event far away and long ago.


Image of Yaron Sheffer

Yaron Sheffer

March 24, 2021 at 4:46 pm

Nice report! So a known system has erupted. That's nice, too. But I thought most of my nuclei were fabricated in a supernova, rather than in a regular nova, at least it sounds more impressive :^) Yes, it happened long ago, but not necessarily far away (astronomically speaking).

You must be logged in to post a comment.

Image of Ben-Williams


March 25, 2021 at 9:46 am

Thanks Bob for this excellent guide to observing the new nova in Cassiopeia. Following your finder charts and those from the AAVSO website link I was able to locate the object without difficulty last night. The nova was clear to see with my 7" Maksutov at 76x despite observing conditions being far from ideal with thin cloud and the gibbous Moon high up. I was also successful in observing with binoculars, with 10x70 the nova was an easy spot and I just managed to glimpse it in 8.5x44. Looking forward to tracking brightness changes over future observations.

You must be logged in to post a comment.

Image of Anthony Barreiro

Anthony Barreiro

March 29, 2021 at 4:34 pm

Thanks very much Bob! I saw the nova through 10x42 image-stabilized binoculars at the beginning of dawn, around 5:30 am PDT, the past three mornings. Saturday I was "pretty sure", yesterday I was confident I had found the nova, and this morning it was a snap. Your chart and directions make it very easy to find. Visually the nova is entirely unremarkable, just one of a wide pair of stars around 8th magnitude. As with so many things in the sky, you need to understand what you're looking at to appreciate it.

I'm impressed that Mr. Nakamura would notice a 9.6-magnitude star where none had been before. Do you know if he found it by visually inspecting his images, or did he use software?

You must be logged in to post a comment.

You must be logged in to post a comment.