NGC 2261

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NGC 2261
Reflection nebula
Variable Nebula
Hubble's Variable Nebula - NGC 2261.png
An image of NGC 2261 by the Hubble Space Telescope
Credit: HST/NASA/JPL/Judy Schmidt
Observation data: J2000.0 epoch
Right ascension6h 39m 10s[1]
Declination+8° 45′[1]
Distance2,500 ly
Apparent magnitude (V)9.0
Apparent dimensions (V)2′
DesignationsHubble's Variable Nebula,[1] 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.

Observing history[edit]

NGC 2261 was discovered in 1783 by William Herschel.[2]

NGC 2261 was imaged as Palomar Observatory's Hale Telescope's first light by Edwin Hubble on January 26, 1949,[3] some 20 years after the Palomar Observatory project began in 1928. Hubble had studied the nebula previously at Yerkes and Mt. Wilson.[3] Hale had taken photographic plates with a 24-inch (60.96 cm) reflecting telescope in 1916.[4] Also, plates were taken using the same telescope in 1908 by FC Jordan, this allowed Hale to use of a blink comparator to study any changes in the nebula.[4]

NGC 2261 was imaged by the Hubble Space Telescope, and an image of the nebula was released in 1999.[5]


The star R Monocerotis has lit up a nearby cloud of gas and dust, but the shape and brightness slowly changes visibly even in small telescopes over weeks and months, and the nebula looks like a small comet.[6]

One explanation proposed for the variability is that dense clouds of dust near R Mon periodically block the illumination from the star.[7] This casts a temporary shadow on the nearby clouds.[8]

See also[edit]


  1. ^ a b c "NGC 2261". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2007-04-11.
  2. ^ "Hubble's Variable Nebula". Retrieved 2018-07-25.
  3. ^ a b "Citizen Science".
  4. ^ a b Hubble, E. P. (1916). "The variable nebula NGC 2261". Astrophysical Journal. 44: 190. Bibcode:1916ApJ....44..190H. doi:10.1086/142284.
  5. ^ "Hubble's variable nebula (NGC 2261)". Retrieved 2018-07-25.
  6. ^ "Hubble's Variable Nebula, NGC 2261". Planetary Science Institute. 2010-10-15. Retrieved 2018-07-25.
  7. ^ Arny, T. T.; Bechis, K. P. (1978). "A model for the cometary nebula NGC 2261". The Astrophysical Journal. 226: 455. Bibcode:1978ApJ...226..455A. doi:10.1086/156627.
  8. ^ "NGC 2261: Hubble's Variable Nebula | Science Mission Directorate". Retrieved 2018-07-25.

External links[edit]