FU Orionis

FU Orionis is a variable star in the constellation of Orion, that in 1937 rose in apparent visual magnitude from 16.5 to 9.6, and has since been around magnitude 9. For a long time it was considered unique, but in 1970 a similar star, V1057 Cygni, was discovered, and a number of additional examples have been discovered since then. These stars constitute the FU Orionis class of variable stars, GCVS type FU, often nicknamed FUors. These stars are pre–main sequence stars which display an extreme change in magnitude and spectral type.