[AZ-Observing] Hubble's Variable Nebula
- From: BillFerris@xxxxxxx
- To: az-observing@xxxxxxxxxxxxx
- Date: Sun, 18 Jan 2004 13:24:02 EST
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
ultraviolet 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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