|Observation data: J2000.0 epoch|
|Right ascension||6h 39m 10s|
|Apparent magnitude (V)||9.0|
|Apparent dimensions (V)||2′|
|Absolute magnitude (V)||-|
|Other designations||Hubble's Variable Nebula, Caldwell 46|
|See also: Diffuse nebula, Lists of nebulae|
NGC 2261 (also known as Hubble's Variable Nebula or Caldwell 46) is a variable nebula located in the constellation Monoceros. It 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.
- "SIMBAD Astronomical Database". Results for NGC 2261. Retrieved 2007-04-11.
- "A model for the cometary nebula NGC 2261". SAO/NASA ADS Astronomy Abstract Service. Retrieved 2010-11-28.
- European Homepage for the HST – Hubble photos and information on NGC 2261
- wikispaces.com – Images by amateur astronomers
- NGC 2261 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
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