Nova in Cassiopeia

Page updated 25 March 2021

A nova has appeared in the constellation of Cassiopeia. Novae are stars that suddenly undergo an increase in brightness of typically over a thousand-fold, so what looks like a new star appears. In this case, the nova is 8th magnitude, which is visible using binoculars. The star is likely to fade over a period of weeks.

Recent observations suggest that the star is remaining at close to its discovery brightness of about magnitude 7.8. Many novae decline rapidly in brightness within days of their peak, but this nova is not showing any signs of doing this after a week of observation and may be in the rare class with a flat-topped light curve. The reasons for the difference are unknown. So this object will continue to be of interest to astronomers and it is well worth watching over a period of time.

The object was discovered on 18 March by Japanese amateur astronomer Yuji Nakamura, who reported it to Japan’s national observatory. It has been confirmed as a nova on the basis of its spectrum. The nova is at RA 23h 24m 47.60s, Dec +61º 11′ 14.0″ (Epoch 2000.0)

The region of sky is easily visible in the evening, so use the maps below to locate it for yourself. But it is in a fairly crowded part of the Milky Way, and is close to another star of similar brightness, so compare your view carefully with the step-by-step maps below. The nova is very close to the well-known star cluster M52, and also to the Bubble Nebula, a popular target for deep-sky imagers.

Step 1. Cassiopeia is the well-known W shape of stars in the north-western evening sky. Find the stars Beta Cassiopeiae and also Iota Cephei to the north of Cassiopeia, then locate fifth-magnitude 4 Cas between them. The nova is shown by a cross just below 4 Cas.
Step 2. A narrower field of view with Beta and Iota at lower left and top right, and 4 Cas in the middle. The blue circle indicates a five-degree field of view, typical of binoculars. Now locate the two sixth-magnitude stars in the rectangle. The nova is shown by a cross.
Step 3. This map shows stars to magnitude 12 within the rectangle. The nova is between the two sixth-magnitude stars, but is close to a ninth-magnitude star. The cluster of stars at the top of the map is the open cluster M52. All maps adapted from SkyMap.
NCas2021close mags
On this version of the chart, the magnitudes of some nearby stars have been added to help in estimating the nova’s magnitude (click to enlarge). These stars are not official photometric stars so the results should not be used for accurate reports. For accurate estimates, the AAVSO chart below should be used
A close-up photograph of the nova close to the 9th-magnitude star, taken by T. Noguchi, Katori, Japan on the morning of 19 March. The nova was estimated at magnitude 7.8.
Nova Cas (circled) on 19 March, photographed with Sony A7S camera and 72 mm f/6 lens. The nova is approximately mag 7.7. Photo: Robin Scagell
This wide-field comparison chart from the American Association of Variable Star Observers gives magnitudes for comparison stars that can be used for making estimates of the nova’s brightness. The scale is comparable with the second of our finder charts above, the one that includes the binocular field of view in blue. Note that the labels are for the magnitudes of the stars with the decimal point omitted, so the star labelled 50 is in fact 4 Cas, which has a magnitude of 5.0. Chart from AAVSO.
Photo taken on 21 March by Ian Morison using an 80 mm Optic Star f/6 refractor and Altair Astro 294C PROTEC camera.  A stack of 49 x 10 second exposures

We’re pleased to say that this page is proving very popular and useful in helping visitors to locate the nova. The Society for Popular Astronomy has been assisting people in discovering the night sky for more than 65 years. Membership rates are very reasonable, so please read about what we offer and consider joining!