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See a nova or “new” star. V1405 Cas is now visible to the eye

A starfield with an open star cluster and a nebula, with one star (the nova) marked.
View at EarthSky Community Photos. | Eliot Herman caught Nova V1405 Cas [between tickmarks] on May 11, 2021, from Mayhill, New Mexico. He wrote: “Nova V1405 Cassiopeiae has brightened to magnitude 5.4. The nova was magnitude +7.8 since shortly after its discovery in March 2021, but it suddenly brightened. Magnitude 5 novas are uncommon. The nova is visible for about an hour before dawn. The open cluster M52 and the Bubble Nebula are also shown in the photo.” Thank you, Eliot!

First spotted in March, Nova V1405 Cas has suddenly flared in brightness over the past week, enabling observers to spot it without binoculars or a telescope. You can see it too, if you observe from a dark-sky site and know just where to look! Plus … what is it? It’s not a supernova or exploding star. What causes a star to appear where no star was before? You’ll find charts, photos from our community, and an explanation here.

Japanese photographer Yuji Nakamura spotted a nova located in the direction of the constellation Cassiopeia the Queen on March 18, 2021. At that time, this light in our sky – which has been named V1405 Cas – was shining at about magnitude 9.6, much too faint to see with the eye. Just a few days later, though, the nova had brightened to about magnitude 7.6, making it bright enough to be visible with binoculars. Now that the nova is around magnitude 5.5, those with keen eyesight and dark skies can hunt it down without any optical aid at all, though it may help to first locate it with binoculars or a telescope and then your eyes alone. The charts below will help you star hop to the nova.

Cassiopeia is very low on the northern horizon. Your viewing location will have to be free of trees, buildings and hills and free of light pollution, or you can wait until the middle of the night when Cassiopeia rises a bit higher. The nova is between the W shape of Cassiopeia and the house shape that makes up Cepheus. Take the two stars on the right side of Cassiopeia’s W shape and use them to draw a line toward Cepheus. Extend the line for approximately the same distance as the two stars are apart from each other and start looking for a little star cluster known as M52. Then look just off of M52 and use the map to pinpoint the nova. The charts and photos shown here will guide you. The first star chart is for March, but the location of the nova between Cassiopeia and Cepheus has not changed, even though the constellations’ locations have shifted a bit on the sky’s dome.

What is a nova? This particular object is likely what’s called a classical nova, seen only once (so far), caused by two stars’ interactions in a binary star system. The system causing a nova consists of a white dwarf and likely a star similar to our sun, in an extremely close orbit, perhaps lasting only hours (contrast that orbit to Earth’s orbit around the sun of 365 days). Being so close, the more massive white dwarf siphons gas – mostly hydrogen – from its companion star. An accretion disk forms around the white dwarf, which, in turn, deposits a hydrogen layer onto the surface of the white dwarf. This causes temperatures and pressures to build, finally creating a runaway thermonuclear reaction. As the COSMOS The SAO Encyclopedia of Astronomy explains:

The energy released through this process ejects the majority of the unburnt hydrogen from the surface of the star in a shell of material moving at speeds of up to 1,500 km/s. This produces a bright but short-lived burst of light – the nova.

Novae happen much more often than supernovae, but only a few of them reach magnitudes visible to the unaided eye. One of the last novae that could be spotted without optical aid was in 2013 in the constellation Delphinus, so take advantage of this nova while it lasts!

V1405 Cas is located at right ascension 23h 24m 48s, declination +61° 11′ 15″.

Star chart with constellation lines showing the nova as a red dot.
Follow the bottom 2 stars in the M- or W-shaped constellation Cassiopeia to find the new nova. Image via Bob King/ Sky & Telescope.
Star chart with closeup on nova region.
You can star hop from moderately bright stars to the nova as shown here. Image via Bob King/ Sky & Telescope.
Star field with oblects labeled including bright nova.
View at EarthSky Community Photos. | David Hoskin in Halifax, Nova Scotia, Canada, captured this photo of the nova on May 11, 2021. He wrote: “Nova Cas 21 has brightened dramatically and can now be seen with the unaided eye from a dark-sky site. I captured this image of Nova Cas 21 and its surroundings early this morning. Nova Cas 21 is currently at least as bright as HIP 115395, which is a +5.55-magnitude star.” Thanks, David!
Dark sky with trees below and star pinpointed with markers.
View larger. | This wider shot shows how nova V1405 Cas can be spotted without optical aid using just your eyes. (Nova indicated with red hashmarks just left of top of tallest tree.) Image via Project Nightflight. Thank you, Project Nightflight!
Labeled starfield with box around the nova.
View at EarthSky Community Photos. | Tara Mostofi in California and Alexandru Barbovschi in Moldova collaborated on this image of nova V1405 Cas on March 21, 2021. You’ll see it inside the green square (and inset) on this image. Thank you, Alexandru and Tara!

Bottom line: The nova in Cassiopeia named V1405 has flared to magnitude 5.4, allowing observers to spot it without the help of telescopes or binoculars.

May 13, 2021

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