Deep Sky Astrophotography

A Lobster Claw, reaching out to a Bubble

The constellation of Cassiopeia is an easy to spot target, even from a light-polluted inner city location. In the close neighborhood of Cassiopeia are some very attractive areas of the night sky. One of those regions is the “Lobster Claw Nebula”, catalogued as “Sharpless 157” or “Sh2 157”. The nebula is formed by huge clouds of gas, mainly hydrogen, oxygen and sulfur. Under certain conditions the gas molecules in those clouds can emit light. While each individual molecule does only contribute a tiny amount of light, there is a lot of gas around. And this light can be made visible by modern cameras. You just need specific filters, which only let pass the specific wavelength of the involved gases. Plus, you need to be patient, as imaging faint clouds of gas takes a lot of time. To make this image, I had to collect nearly 30 hours of light.

One the right top of the image you’ll find a structure, that has the distinct shape of a sphere. Well, it is not a perfect sphere, as it is slightly elongated from North to South. One could also say, it is rather an egg than a sphere. Despite geometrical imperfections, this object is area is called “Bubble Nebula”. It can be found in many catalogues, such as the New General Catalogue (NGC 7635), the Sharpless Catalogue (Sh2 162) or the Caldwell Catalogue (Caldwell 11). The structure is created by the stellar wind from a massive hot star in the center of the bubble.

The colors of the nebulae are no true colors. The light resulting from hydrogen and sulfur is red, while oxygen emits light in a wavelength between blue and green. In order to better reveal the structure of the nebulae, the specific signals of each gas were mapped to the three “basic colors” red, green and blue. However, the colors of the stars are true colors.

So far this is my deep sky image with the longest imaging time:
- 181 frames of Hydrogen Alpha with 3 minutes each, thus 9 hours 6 minutes
- 194 frames of Oxygen III with 3 minutes each, thus 9 hours 42 minutes
- 182 frames of Sulfur II with 3 minutes each, thus 9 hours 6 minutes
- 16 frames of Red with 2 minutes each, thus 32 minutes
- 20 frames of Green with 2 minutes each, thus 40 minutes
- 22 frames of Blue with 2 minutes each, thus 44 minutes

The image was taken in La Palma over several nights, from no moon present to full moon. It was done with a Newtonian Telescope of 430 mm focal length and a cooled 12 bit monochromatic astronomy camera. The editing was done solely in PixInsight.

La PalmaLa Isla BonitaCanary IslandsLobster Claw NebulaSharpless 157Sh2 157Bubble NebulaNew General CatalogueNGC 7635Sharpless CatalogueSh2 162Caldwell CatalogueCaldwell 11ConstellationCassiopeiaH alphaHydrogen alphaOxygen IIISulfur IIRGBCold GasDust CloudsEmission Nebula