A ‘new star’ became visible last weekend and is getting brighter and brighter.
It started, as all modern astronomical warnings seem, with one tweet, then two. In the early morning of March 19, we saw that a nova was discovered in the constellation Cassiopeia the Queen near the border with Cepheus. At the time, the nova was +10 ‘with a bullet’ strength and was still glowing. That same night came a formal notice from the American Association of Variable Star Observers (AAVSO) with the 735 warning about the discovery of the first Nova in Cassiopeia for 2021, Nova Cassiopeiae 2021 or N Cas 2021.
The discovery was made by the Japanese observer Yuji Nakamura on the night of March 18, 2021, and the newly visible star had an initial magnitude of +9.6.
Current Visibility: Will Nova Cassiopeiae Brighten Further In 2021?
At the time of writing, N Cas 2021 is still shining with a power of +7. That puts it within easy reach of binoculars, and when it gets much brighter, it’s visible to the naked eye from a dark-sky location.
In late March, Cassiopeia is low at dusk to observers in the northern hemisphere in the northwest and descends towards a lower peak around midnight before ascending northeast in the early hours of the morning. The moon is now growing towards full on March 28th, after which it will fade and begin to leave the twilight scene.
The + 5 Magnitude Star 4 Cassiopeiae is nearby and is a good guide star. Another well-known deep sky target is just over half a degree from Nova Cas 2021, the open cluster Messier 52 with a magnitude of +6.9. Nova Cas 2021 is roughly equidistant between the stars Beta Cassiopeiae and Iota Cephei to the naked eye.
A wide field finder diagram for Nova Cas 2021. The red inset is the field for the close-in diagram (below). Photo credit: Dave Dickinson / Stellarium.
The coordinates for Nova Cas 2021 are Right Ascension (RA) 23 hours 24 minutes and 48 seconds, declination +61 degrees 11 minutes and 15 seconds. Stars hop through the field and compare the nova with nearby stars of known brightness to find the nova and measure its size. You can make your own custom finder charts for Nova Cas 2021 on the AAVSO website.
A 10 degree finder diagram with “true view” (versus inverted), centered on Nova Cas 2021. Photo credit: Das AAVSO
This particular nova is located approximately one degree outside the galactic plane, a standard region along which novae normally occur. Classical novas occur when a white dwarf orbits a main sequence star in a tight hug and draws in material that then accumulates or concentrates around the white dwarf. The material then compresses around the white dwarf, warms up, and eventually ignites in an out of control fusion process. A sub-category of repeating eruptive variable stars is known as cataclysmic, or recurring novae. T Pyxidis and U Scorpii are good examples of this subclass.
An artist’s idea of a nova in the act of formation. NASA / CXC / M. Weiss
The exact distance to Nova Cas 2021 is not yet known, but most of them peak around an absolute magnitude of -8 and – like extragalactic supernovae – hold great promise for use as standard distance measuring candles. ‘If’ + 7th magnitude is the high point for Nova Cas 2021, that would mean it’s about 30,000 to 32,000 light years away, on the edge of the outer arm of the Milky Way galaxy, just beyond the Perseus arm … but if so it brightens it can be considerably closer.
Received another spectrum from Nova Cas 2021. Strong emission lines for hydrogen balmer. Multiple helium emission lines and possibly nitrogen (N III). Much clearer conditions than last night! Meade LX10 8 “, ZWO ASI178MM, 50 × 5 seconds. Pic.twitter.com/LRritCUPBP
– Dr. Adrian Jannetta ??????? (@AdrianJannetta) March 21, 2021
The last good nova with the naked eye for the northern hemisphere was Nova Delphini 2013 in the tiny whale constellation of Delphinus the dolphin about eight years ago. On average, we get a good galactic nova with the naked eye about once every decade.
Here is our list of novae observed over the past century:
Novas of the 20th and 21st centuries with the naked eye. Adapted to our latest deep-sky field guide. Photo credit: Dave Dickinson
If the patch of sky where Nova Cas 2021 is currently located seems familiar, it could be because it is only six degrees away from Tycho’s supernova, as astronomer Tycho Brahe noted in 1572.
Tycho’s star, seen in 1572. Wikimedia Commons / Public Domain.
Unfortunately, galactic supernovae are much rarer cosmic beasts. Although we see several per year in distant galaxies, we haven’t had any good ones in our own galactic neighborhood since the advent of telescopic astronomy four centuries ago. Spica (Alpha Virginis) and Betelgeuse are good candidates around, though both are well above the 50 light year kill zone and will simply put on a good show. Betelgeuse gave us all a break in late 2019 to early 2020 when it clearly subsided, but seems to be returning to its old self for the time being.
If the skies are clear, be sure to find Nova Cas 2021 tonight. It could be the “cosmic nova show” for this decade.
Main Image: Now You See It … Nova Cas 2021. Photo Credit and Copyright: Mary McIntyre
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