A rare 'recurrent nova' event is visible to the unaided eye in the constellation of Ophiuchus this week.
- RS Ophiuchi (RS Oph) is a recurrent nova system, located about 5 000 light-years away from Earth, with a recurrence rate of about 15 - 20 years.
- Its last outburst took place in 2006.
The 2021 outburst was spotted by Keith Geary from Ireland at 21:55 UTC on August 8, when the brightening increased from magnitude +12 to +5 -- about 600-fold.
On August 10, variable star observer Filipp Romanov of Yuzhno-Morskoy, Russia, reported the magnitude has increased further to +4.6.
This system has an apparent magnitude of about 12.5 in quiet phases but during outbursts, such as observed in 1898, 1933, 1958, 1967, 1985, 2006, and 2021, it can average about magnitude 5.
The recurring nova is produced by a white dwarf star and a red giant in a binary system.
Only 7 star systems in the whole Milky Way galaxy are known to produce such explosions, said Dr. Tony Phillips of SpaceWeather.com.
"At 5th magnitude, the current outburst is visible to the unaided eye, albeit just barely," Phillips said.
"Binoculars or a telescope will allow you to see it with ease. Look south after sunset. Ophiuchus hangs high in the sky just above the better-known constellations Scorpius and Sagittarius."
The last large outburst of RS Oph took place in February 2006 when it reached a visual magnitude of 4.5:
Recurrent nova in RS Ophiuchi on February 23, 2006 as seen from Mt. Laguna, California, US. Credit: Robogun
If you are new to night sky watching, you can use a mobile app to locate Ophiuchus within a minute.
Featured image credit: RS Ophiuchi outburst taken by Ernesto Guido, Marco Rocchetto & Adriano Valvasori on August 9, 2021 @ Remotely from Australia through TELESCOPE LIVE network https://telescope.live/ (via SpaceWeatherGallery)