|NGC 2261 "Hubble's Variable Nebula": Emission & Reflection Nebula (Monoceros) RA: 06h 39.2m / DEC: +08° 44'.9|
Instrument: 10-inch Starfinder
William Herschel was observing the night after Christmas 1783 when R Monocerotis drifted into the field of view. Enveloping the star, was a bright fan-shaped nebulosity. "Comet?" surely must have been the first thought to enter his mind. But this nebula never flinched and the great astronomer logged it as the second in his fourth class of objects: planetary nebula. Today, Herschel's discovery is cataloged as NGC 2261 but is better known as Hubble's Variable Nebula.
NGC 2261 earned its popular moniker in 1916 when a young Edwin Hubble discovered that the nebulosity varied in brightness and shape. Lowell Observatory astronomer C. O. Lampland conducted a photographic study of this object from 1916 to 1951. Lampland produced 900 photographs and was able to detect variability over periods as short as four days. Astronomers believe this variability is caused by the shadows cast by foreground material passing across the face of the nebulosity.
Today, we know that powerful stellar winds from a hot, young star has distorted surrounding matter to shape the nebulosity we see. Much of the nebulosity is visible because of light scattered by smoke-sized particles. This is a classic example of a reflection nebula. However, the tremendous ultraviolet radiation pumped out by R Mon also causes some gases in the nebula to fluoresce and glow. This is the emission portion of the nebulosity.
The view in my 10-inch Newtonian is captured in the sketch at left, which was made at 190X. The fan-shaped nebulosity extends from a 10th magnitude "star" to the north. Star, is in parentheses because the star is shrouded within a cocoon of nebulous materia and cannot be observed visually. The brightest portion of the fan arcs directly north over a distance of about 1'.5. A fainter, narrow streamer reaches first to the northeast then northward for 2'. This is usually an easy object for small apertures under a dark sky, a true showpiece of the celestial carnival.
You'll find this fascinating object about a degree to the south-soutwest of 4.7 magnitude 15 Monocerotis.
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Revised: January 19, 2004 [WDF]