Hubble's Variable Nebula (NGC 2261)
Hubble's Variable Nebula (NGC 2261) is a cometary nebula (a type of reflection
nebula) in the constellation Monoceros whose
apex star is the peculiar variable R Monocerotis. The variability of R Mon
was discovered at Athens Observatory in 1861, but it was not until 1916
that Edwin Hubble discovered that the nebula itself
varies, over timescales as short as a few weeks. Carl Lampland at Lowell
Observatory carried out a 30-year study of the nebula and found that
it changed in apparent size by as much as 1 arc-second in 4 days butt that
its variability was not synchronized with changes of brightness in R Mon
itself. The nebula's variability is presumed to be due to dust clouds orbiting
close to the star, blocking its light and casting shadows.
NGC 2261 is a source of CO emission and has a temperature of about 810 K.
It glows at magnitude 10 and has a high surface brightness, making it an
easy object for an amateur 8-inch telescope.
AND STAR CLUSTERS