Variable Nebula (NGC 2261) is a small 2 x 4 arcminute
nebula found in the constellation Monoceros.
One suggestion proposed for the observed variability
is due to dust clouds near R Monocerotis
periodically changing the nebula's illumination.
The image was a total of 6 hr 20 min exposure with a
12.5” f/9 RCOS telescope and SBIG STF8300c camera (OAG
on a Paramount ME (19 x 1200 sec lights @-15o C; 30 darks;
128 bias; 128 flats); Software: Sky X, MaxIm DL6,