The holidays ended and my daily routine pretty much back to normal, I was able
to take advantage of a break in the winter weather to do some observing last
night. The highlight of the evening was NGC 2261, popularly known as Hubble's
Variable Nebula.

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. Sir William
described his IV-2, "Considerably bright and fan-shaped. About 2' long from the
center."

Today, Herschel's discovery is cataloged as NGC 2261 but is better known as
Hubble's Variable Nebula. It earned this moniker in 1916 when a young Edwin
Hubble discovered that the nebulosity varied in brightness and shape. Today, we
know that powerful stellar winds from a hot, young R Monocerotis distort
material surrounding the star, and this action produces 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 unltraviolet radiation pumped out by R Mon also excites some gases
within the surrounding cloud, causing them to fluoresce and glow. This is the
emission portion of the nebulosity.

The view in my 10-inch Newtonian is captured in a sketch at my website:
http://members.aol.com/billferris/n2261.html

Observing at 190X, the fan-shaped nebulosity extends from R Mon to the north.
The brightest portion arcs directly north over a distance of about 1'.5. A
fainter but longer streamer reaches first to the northeast then northward for
2'. This is an easy object for small aperture under a dark sky, a true
showpiece of the celestial carnival. It's really a shame Hubble's Variable
Nebula was not included in the Herschel 400 observing list. It would easily
rank as one of the most interesting objects, from both visual and physical
perspectives.

You'll find this fascinating object about a degree to the south-soutwest of 4.7
magnitude 15 Monocerotis.

Regards,
Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
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