NGC 2261
| Reflection nebula | |
|---|---|
| Variable Nebula | |
 | |
| 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 |
| Physical characteristics | |
| Radius | ~0.5 ly |
| Designations | Hubble's Variable Nebula,[1] Caldwell 46 |
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 | edit source]The first recorded observation of the nebula was by William Herschel on 26 December 1783, being described as considerably bright and 'fan-shaped'.[2] It had long been designated as H IV 2, after being the second entry of Herschel's class 4 category for nebulae and star clusters, in his catalogues of nebulae.[3]
NGC 2261 was imaged as Palomar Observatory's Hale Telescope's first light by Edwin Hubble on January 26, 1949,[4] some 20 years after the Palomar Observatory project began in 1928. Hubble had studied the nebula previously at Yerkes and Mt. Wilson.[4] Hubble had taken photographic plates with the Yerkes 24-inch (60.96 cm) reflecting telescope in 1916.[5] Plates were taken using the same telescope in 1908 by F.C. Jordan, allowing Hubble to use a blink comparator to search for any changes over time in the nebula.[5]
NGC 2261 was imaged by the Hubble Space Telescope, and an image of the nebula was released in 1999.[6]
A timelapse of NGC 2261 was taken over a period of 6 months by over 20 amateur astronomers at the Big Amateur Telescope from October 2021 – April 2022. In August 2022, the project was resumed as NGC 2261 came out from behind the Sun.[7]
Descriptions
[edit | edit source]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.[8]
One explanation proposed for the variability is that dense clouds of dust near R Mon periodically block the illumination from the star.[9] This casts a temporary shadow on the nearby clouds.[10]
See also
[edit | edit source]References
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External links
[edit | edit source]
- 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
