Object of the Week December 28, 2014 - NGC2359 Thors Helmet

[Dragan]

NGC2359
Sh2-298

Canis Major

Emission Nebula

07 18 31.0
-13 14 00

Mag: Brightness varies among sources but 10th magnitude seems to be a good average

Size: 13' x 11'

Thors Helmet, in my opinion, has to be one of the greatest sights in the winter sky. How it never made Messiers list I'll never know as it makes for a spectacular object in all size telescopes.

15,000 light years away in Canis Major, NGC2359 is powered by a Wolf-Rayet star. WR's are typically extremely massive unstable stars not too far off from going supernova. NGC2359 is presumed to lay in a region of large amounts of hydrogen gas. As NGC2359's WR star, HD 56925, ejects and loses material at extremely high speeds, it's this ejected material that is colliding with the hydrogen in the region that is giving this fantastic object its shape and detail seen in amateur telescopes. The helmet shape we see is actually a bowshock, or shell, formed between the stars ejected matter and the interstellar medium, not unlike the Bubble Nebula NGC6888 in Cygnus. DSF member Reiner has a great page on WR stars, explaining the science better than I could ever dream of. http://www.reinervogel.net/index.html?/WR/WR_e.html Here you'll also find a listing for NGC2359

Under the night sky, Thors Helmet isn't too difficult to locate. Approximately 9º northeast of Sirius, NGC2359 appears as a large diffuse nebula and is visible in most telescopes. Compromising of excited gas, this is one object where you'll want a filter. Narrowbands work best with OIII being the way to go. Relatively dark skies with an OIII and this object can be seen in scopes down to about 4" as a small faint glow. In larger aperture scopes and a filter, you'll star to make out the "dome" of the helmet as a slightly out of round bubble laced with delicate tendrils similar to fine detail in the Veil. The detail is quite astounding actually. In my 25" I have no particular difficulty in seeing darker spots and irregular structure on the helmets dome highlighted by brighter edges.The two westward protrusions so commonly visible in photographs, with the southernmost arm being brighter than its northern counterpart is also visible.

If you're out observing these winter (summer in the south) nights, be sure to take a look at Thors Helmet. Its a fantastic object that isn't too particularly difficult and offers a wealth of detail in all manner of scopes. And as you enjoy this OOTW, ask yourself how is it that an object as fine and as close to M41,M46, M47 and even M42 as this one is, how is it that Messier left it off of his list. I guess he just must have overlooked this gem OR it was just so plainly obvious it wasn't a comet he decided not to catalog it. (But then, M42 DID make his list.)

As always,
"Give it a go and let us know!
Good luck and great viewing!"


1491 (http://www.deepskyforum.com/attachment.php?attachmentid=1481&d=1420171546)
Above photo Credit & Copyright: Mike Halderman/Caltech/Anglo-Australian Observatory (AAO)/Digitized Sky Survey 2


1492
Above photo credit & copyright: Robert Gendler

[Uwe Glahn]

I had an observation with a small 4" reflector - pretty easy nebula with [OIII] filter.

With bigger aperture - say 16" my personal challenge was always to detect the fainter inner arc which started from the WR star 1,2' to the north.

16", 129x, [OIII], NELM 6m5+
1489

[glxytrios]

This is one of my favorite objects. When I first observed it some years ago, I didn't know it was called Thor's Helmet. The brightest part reminded me of a tadpole so I thought of it as the "Tadpole Nebula". Salamander tadpoles have two structures on the head called balancer organs, so it was a salamander tadpole because of the two brightest streamers that were visible to me in my 14' scope at the time. Then I learned it was called Thor's Helmet. Oh well, I yield - it's Thor's Helmet. A beautiful object in my 20" Dob with OIII filter. Clear skies, glxytrios (aka Miles)

[Howard B]

I had a good view of Thor's Helmet this past November with my 8 inch f3.3 Newtonian:

"Pretty good! Thor's Helmet shows its main structure with the OIII, and is faintly seen without the filter with a beautiful Milky Way starry back drop. This will look even better when it's near the meridian, as it's only halfway there now. 59x, 21.60 SQM. 9100 feet, MKVC."

1493 1494

I've rarely had the chance to see 2359 because of weather and it's low altitude in the Oregon sky, but with the few peeks I've had I know there is a wealth of detail here for larger scopes.

[nicoscy]

Last night with average to good seeing, I managed to see Thor's helmet with a 50mm f6.67 APO, both with OIII and without filter.

Without a filter the view was of a very faint patch of nebulosity, barely visible against the sky background.

With OIII filter, the object took the characteristic shape of the bubble plus the beginnings of the "wings" of the helmet, making the object appear orthogonal to the eye due the beginning of the wings being "attached" to the helmet.

[RolandosCY]

I can confirm NicosCY observation. I was amazed on how distinct NGC 2359 was with an OIII through the little refractor. I could even tease out at times the wings structure. Without the filter it was an averted vision object at the edge of visibility...