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

Reflection nebula
Variable Nebula
An image of NGC 2261 by the Hubble Space Telescope Credit: HST/NASA/JPL/Judy Schmidt
Observation data: J2000.0 epoch
Right ascension	6h 39m 10s[1]
Declination	+8° 45′[1]
Distance	2,500 ly
Apparent magnitude (V)	9.0
Apparent dimensions (V)	2′
Constellation	Monoceros
Designations	Hubble's Variable Nebula,[1] Caldwell 46
See also: Lists of nebulae

Observing history

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]

Descriptions

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

• NGC 1555
• New General Catalogue

References

External links

Wikimedia Commons has media related to NGC 2261.

• European Homepage for the HST – Hubble photos and information on NGC 2261
• wikispaces.com Archived 2013-02-09 at archive.today – Images by amateur astronomers
• Astrobiscuit: Seeing The Speed Of Light fun and educational video about variable nebula and the amateur community observing them
• NASA Astronomy Picture of the Day: NGC 2261: Hubble s Variable Nebula (November 8, 2017)
• NGC 2261 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

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