Thor's Helmet / by Conor Cunningham

Lurking 15 000 light years away is a star rapidly losing mass. So massive is this star in fact, that it can by way of its own solar winds create gas clouds 30 light years across. HD 56925 is estimted to be 16 times the mass of our sun and is lossing enormous amounts of its  every day.

The result of this stellar wind and mass loss is Thor's Helmet (NGC 2359), an emission nebula; a collection of elements excited by the stellar windws.

If you point a good telescope at it and expose the attached camera correctly for 22 hours you can wind up with an image like this.

Thor's Helmet, NGC 2359. Sulphur II, Hydrogen Alpha and Oxygen III filters used for RGB respectively.

The image is composed of 88 x 15 minute exposures. Three filters were used: Sulphur II for the Red, Hyrdrogen Alpha for the green and Oxygen III for the blue. This is known as the hubble palette. When an Oxygen atom is excited by the stellar wind, its electrons gain energy. When they lose that energy they give it of as light. By using the aforementioned filters one can capture the specific wavelengths of the various elements.

For those interested in the instrument used to take this, the full set of details can be found here :