In a rare move, a sleepy cataclysmic variable blows its top and suddenly becomes a nova.
The dwarf nova V392 Persei, which only gets as bright as magnitude 14 during outburst, appears to have undergone a rare nova outburst. The sudden and steep brightening was discovered photographically on April 29th by Yuji Nakamura of Japan, who recorded the star at magnitude 6.2. Spectra obtained shortly thereafter with the 2.4-meter Hiltner telescope on Kitt Peak confirm the explosion as a nova.
Had the Moon not brightened the sky, the outburst would have been visible with the naked eye from a dark site.
As of this morning, May 1st, V392 Per has faded a magnitude to 7 and remains an easy catch in binoculars. There's no telling whether it will brighten further, continue to fade, or hit a standstill. One thing is certain: dwarf novae rarely explode as novae. This is something very special, and I encourage you to grab your binoculars for a look.
Dwarf novae are binary stars where the more massive star, a white dwarf, robs matter from a closely-orbiting lower mass companion. As the material spins into an accretion disk around the dwarf, variations in its flow and temperature cause the disk to periodically heat up and brighten. Through a telescope, the star swells 2 to 6 magnitudes in just a day or two. Catching one on the rise after seeing it at minimum for weeks is one of the more exciting sights in amateur astronomy.Two of the most famous dwarf novae are U Geminorum in the winter sky and SS Cygni in the summer.
Only once in the history of dwarf novae observations has a star (V1213 Cen) transitioned to a nova. In a nova, material from the disk gets dumped onto the surface of the white dwarf, where it's compressed and heated to ignite in a much more powerful (and brighter) explosion. V392 Per shot up nearly 9 magnitudes and may brighten even more. Eruptions like this are predicted to recur on timescales of 10,000 to 1 million years.
You can stay in touch with the nova's daily behavior by going to the AAVSO website and typing in the star's name in the Pick a Star box. Then, select a link to either review recent observations, make a new light curve, or create a chart.
Use the accompanying AAVSO chart (and/or this more detailed chart) to find the star and estimate its brightness. Start at Epsilon (ε) Aurigae, the star at the apex of the skinny triangle that forms "The Kids" asterism near Capella, then star-hop to the northwest past the "star pair" on the map to the nova.
In both charts, you'll notice a 9.3 magnitude star close to and nearly due east of the nova. It's a nice comparison star to help in seeing the nova's changing brightness over the coming nights. Click to enlarge, download, and print each. North is up in both. Clear skies!
** Update: I estimated V392 Per at magnitude 8.3 on May 2.12 UT. Several people have asked me how far away the nova is. Using the star's parallax from the most recent GAIA data release, it's about 12,700 light years away.