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View Full Version : Object of the Week - January 15th, 2017 - NGC 2346



Paul Alsing
January 17th, 2017, 11:39 PM
Object of the Week - January 15th, 2017 - NGC 2346, The Hourglass Nebula = M 1-10, PN G215.6+03.6, PK 215+3.1
Monoceros
R.A. 07h09m22.5s - 00°48'23" (2000)
Size 60"x50"
Mag; V = 12.5; central star = V651 Mon (mag 11.3-13.5)

NGC 2346 is well placed this time of year, culminating just before midnight. Since it is almost exactly on the celestial equator is can be seen from almost anywhere in the world. Carrying the nickname "The Hourglass Nebula" (it is also known as the "Butterfly Nebula", photos of this planetary nebula leave little doubt as to how it got this name...

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NGC 2346 is a bipolar PN and was discovered by William Herschel in 1785. It is approximately 2,000 light-years away from us and is about one-third of a light-year in diameter. In my 25" f/5 dob it is tiny although fairly bright, even without filtration, but it responds wonderfully to just about any filter, OIII, UHC or my trusty NPB. I saw it as being a bright star with a hazy ring around it, and almost round. Upon pumping up the power I could get a hint of a pinch in the middle, and a hint of the 'wings' to either side. I think I would have seen more detail if the darn central star wasn't so bright!

That central star's history is quite interesting. It is actually a binary star, an A5 main sequence star and a hot subdwarf, in a close orbit of about 16 days. See this page http://www.wolaver.org/space/ngc2346.htm where it is written...

"It is believed that the binary star was originally more widely separated. However, when one component of the binary evolved, expanded in size, and became a red-giant star, it literally swallowed its companion star. The companion star then spiralled downwards inside the red giant, and in the process spewed out gas into a ring around the binary system. Later on, when the hot core of the red giant was exposed, it developed a faster stellar wind, which emerged perpendicularly to the ring and inflated two huge "bubbles." This two-stage process is believed to have resulted in the butterfly-like shape of the nebula." Isn't that fascinating?

As always, give it a go and let us know

Mark McCarthy
January 20th, 2017, 04:41 AM
I saw this last spring from central California, in a 20-inch at 205x: "Visible unfiltered as a star with irregular haze around it. OIII shows a distinct apple-core (bipolar) shape orientated NNW-SSE. No connecting rims to E or W sides."

Very fascinating how the nebula came to have its distinctive shape, thanks for that!

Uwe Glahn
January 23rd, 2017, 07:29 PM
The wings with my 16" were very difficult to detect. I only could pick out some first signs of them. I had to revisit the PN.

sketch: 16", 450x, [OIII], NELM 6m+
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Howard B
January 23rd, 2017, 08:29 PM
I have an observation, but no sketch, from 2000:

"Nice planetary! Round with an indistinct outer edge, but not quite so subtle that they imperceptibly fade into the sky. Bright center which may be dominated by a central star but the seeing is so bad that it's impossible to tell for sure. The bright inner region is very distinct but shows best with the OIII filter. 261x. 20 inch f/5".

I usually remember what an object looked like when reading my notes but I'm drawing a blank on 2346, so it's definitely due for another look.