Dragan
January 5th, 2014, 06:56 AM
NGC2261
Monoceros
RA 06 39 09.5
DEC 08 44 52
Type: Reflection Nebula
Size: 2.0' x 1.7'
Mag: 10 to Variable
Yet another discovery by William Herschel, this time in 1783, NGC2261 is a reflection nebula in the constellation Monoceros. Appearing to fan out northward away from the star R Monocerotis, NGC2261 is a unique object in that its brightness appears to vary over time. For many years the source of its variability was speculated. In 1915, a volunteer astronomer at Yerkes named John Mellish put the first year graduate student Edwin Hubble in charge of determining the source of its variability. A year later in 1916, Hubble published his very first journal paper where several ideas were proposed:
1. The nebula may be rotating and providing us with different views of itself,
2. Matter itself in the nebula was brightening and fading and its “nucleus” (what we know today to be R Mon) had no effect on its variability,
3. Another explanation was the possibility that portions of the nebulosity was being discharged from its “nucleus”.
I quote “nucleus” because it was William Lassell, discoverer of Neptunes moon Triton, who suggested and later corroborated by EE Barnard, that R Mon was not a star but in fact a “true nucleus, such as that of the great spiral in Andromeda.” Using data obtained from the Yerkes Observatory 40” refractor, Hubble knew R Mon to be a variable star and 2261 belonged to a family of nebulae & stars (T Tauri stars) that had pecularities in common with other variable nebula such as, NGC2245, NGC1555 (Hinds Variable), NGC6729 and even NGC7662, the Blue Snowball! (though I haven't done any research on NGC7662, this paper suggests that Hubble believed it to be variable. Does anyone have any information on this?) Unfortunately, none of his theories at the time proved fruitful.
It appears that from a paper (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...489..210C&db_key=AST&high=3353cecba004996) published in 1997, the most accepted theory today is that Hubbles Variable Nebula does not vary due to its host star being variable. It varies due to matter from the dust envelope surrounding R Mon being strewn out into the stellar wind and the light from R Mon being blocked by these clouds. Essentially, opaque clouds of matter that pass between R Mon and NGC2261 are casting shadows onto the nebulas surface and we see it! Pretty interesting!
NGC2261 is an object that is visible in scopes as small as 4 inches, though it'll take more aperture to see its finer detail it isn't an inherently difficult object. It's appearance can change in a period as short as 3 days, making this an object to observe on a regular basis! What did you see the last time you were out?
One little bit of trivia, NGC2261 was the first photograph taken with the 200” Hale Telescope at Palomar in 1948.
And as always,
"Give it a go and let us know!"
1015
The original image taken with the 200" Hale in 1949.
1016
A more recent HST image.
Monoceros
RA 06 39 09.5
DEC 08 44 52
Type: Reflection Nebula
Size: 2.0' x 1.7'
Mag: 10 to Variable
Yet another discovery by William Herschel, this time in 1783, NGC2261 is a reflection nebula in the constellation Monoceros. Appearing to fan out northward away from the star R Monocerotis, NGC2261 is a unique object in that its brightness appears to vary over time. For many years the source of its variability was speculated. In 1915, a volunteer astronomer at Yerkes named John Mellish put the first year graduate student Edwin Hubble in charge of determining the source of its variability. A year later in 1916, Hubble published his very first journal paper where several ideas were proposed:
1. The nebula may be rotating and providing us with different views of itself,
2. Matter itself in the nebula was brightening and fading and its “nucleus” (what we know today to be R Mon) had no effect on its variability,
3. Another explanation was the possibility that portions of the nebulosity was being discharged from its “nucleus”.
I quote “nucleus” because it was William Lassell, discoverer of Neptunes moon Triton, who suggested and later corroborated by EE Barnard, that R Mon was not a star but in fact a “true nucleus, such as that of the great spiral in Andromeda.” Using data obtained from the Yerkes Observatory 40” refractor, Hubble knew R Mon to be a variable star and 2261 belonged to a family of nebulae & stars (T Tauri stars) that had pecularities in common with other variable nebula such as, NGC2245, NGC1555 (Hinds Variable), NGC6729 and even NGC7662, the Blue Snowball! (though I haven't done any research on NGC7662, this paper suggests that Hubble believed it to be variable. Does anyone have any information on this?) Unfortunately, none of his theories at the time proved fruitful.
It appears that from a paper (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997ApJ...489..210C&db_key=AST&high=3353cecba004996) published in 1997, the most accepted theory today is that Hubbles Variable Nebula does not vary due to its host star being variable. It varies due to matter from the dust envelope surrounding R Mon being strewn out into the stellar wind and the light from R Mon being blocked by these clouds. Essentially, opaque clouds of matter that pass between R Mon and NGC2261 are casting shadows onto the nebulas surface and we see it! Pretty interesting!
NGC2261 is an object that is visible in scopes as small as 4 inches, though it'll take more aperture to see its finer detail it isn't an inherently difficult object. It's appearance can change in a period as short as 3 days, making this an object to observe on a regular basis! What did you see the last time you were out?
One little bit of trivia, NGC2261 was the first photograph taken with the 200” Hale Telescope at Palomar in 1948.
And as always,
"Give it a go and let us know!"
1015
The original image taken with the 200" Hale in 1949.
1016
A more recent HST image.