BC Cygni

BC Cygni (BC Cyg, HIP 100404, BD + 37 3903) is a red supergiant and pulsating variable star of spectral type M3.5Ia in the constellation Cygnus.

It is considered a member of the stellar Cygnus OB1 association, and within it the open cluster Berkeley 87, which would place at a distance of 1,673 pc of the Solar System; it is less than a degree north of another variable red supergiant, BI Cygni. According to its Gaia Data Release 3 parallax, it is at about $1,662$.

BC Cygni was found to have a luminosity of and an efective temperature of 2,858K in the year 1900, and a luminosity of  and a temperature of 3,614K in the year 2000. At its brightest and coolest has been calculated to be compared to  at the hottest and faintest. It is one of largest stars known, and currently is times larger than the Sun. If it were in the place of the Sun, its photosphere would engulf the entire inner solar system and reach close to the orbit of Jupiter. With a mass of about, it is estimated that the stellar mass loss, as dust, as the atomic and molecular gas could not be evaluators is $5,418$ per year.

The brightness of BC Cyg varies from visual magnitude +9.0 and +10.8 with a period of 720 ± 40 days. Between around the year 1900 and 2000 appears to have increased its average brightness of 0.5 magnitudes.