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!"


NGC 2359_n.jpg
Above photo Credit & Copyright: Mike Halderman/Caltech/Anglo-Australian Observatory (AAO)/Digitized Sky Survey 2


ngc_2359-aul_gendler.jpg
Above photo credit & copyright: Robert Gendler