NGC 2261

NGC 2261

Reflection nebula
An image of NGC 2261 by the Hubble space telescope. Credit: HST/NASA/JPL.
Observation data: J2000.0 epoch
Subtype	variable nebula
Right ascension	6h 39m 10s
Declination	+8° 45′
Distance	2,500 ly
Apparent magnitude (V)	9.0
Apparent dimensions (V)	2′
Constellation	Monoceros
Designations	Hubble's Variable Nebula,Caldwell 46
See also: Lists of nebulae

NGC 2261 (also known as Hubble's Variable Nebula or Caldwell 46) is a variable nebula located in the constellation Monoceros. The nebula is illuminated by the star R Monocerotis (R Mon), which is not directly visible itself.

NGC 2261 was imaged as Palomar Observatory's Hale Telescope's first light by Edwin Hubble on January 26, 1949, some 20 years after the Palomar Observatory project began in 1928. Hubble had studied the nebula previously at Yerkes and Mt. Wilson.

One explanation proposed for the variability is that dense clouds of dust near R Mon periodically block the illumination from the star.