RS Ophiuchi

RS Ophiuchi is a recurrent nova, which is a variable star and a binary star, consisting of a white dwarf and red giant. It is one of just a very few observed recurrent novae in the Milky Way and has the largest number of recorded eruptions, seven, the first in 1898 and the most recent in 2021. Its frequent recurrence and relative nearness make it of considerable research interest. Characteristics:

• Ophiuchus - constellation.
• 17h50m13.2s - right ascension.
• -06deg42m28s - declination.
• WD and K5.5/M0IIIe - spectral types (the giant star's type varies between M and K even when the nova is quiet).
• about +12.5 - apparent magnitude when quiet, growing to less than +5 during an eruption.
• 2600 pc - distance (note that determinations have been inconsistent and are not fully trusted).