The Elephant Trunk Nebula

The Elephant Trunk Nebula

We return once again to the constellation Cepheus, a constellation that is often ignored by visual observers, but which contains yet another great photographic favorite. The Elephant Trunk Nebula is a dark nebula embedded in the open cluster IC 1396. This is a large open cluster about three degrees across (half the size of the Andromeda Galaxy), that is accompanied by significant emission nebulosity as well as dark dusty nebula intermingled throughout. Visually the cluster has a vague “X” like pattern of stars with some very faint nebulosity that can be gleaned under dark skies and a larger telescope of 8-inches or more. Photographically, the nebula can be captured with any aperture and exposures of only a few minutes. This cluster is an H II star forming region about 3,000 light years from us and is estimated to be only three to four million years old, making it one of our galaxy’s youngest clusters. At three degrees across, the entire cluster and nebula can be captured with a short focal length, while longer focal lengths can focus on the Elephant Trunk itself.

The Elephant Trunk is seen as a smaller portion of this larger nebula and is cataloged as IC 1396A. It is also a member of Canadian astronomer Sidney van den Bergh’s list of reflection nebula as number 142 and is most often designated as “SAC vdB 142” for its place in the well-known Saguaro Astronomy Club catalog of deep sky objects. Scientists studying dark nebula in the region will refer to it as “Globule A”.

Seeing the Elephant Trunk itself takes a little imagination. Using the image shown here, the roughly circular feature to the right of center would be the elephant’s head. Imagine it looking to the left in profile, towards the bright star. The trunk is then the long feature seen at the far left extending from the bottom to about halfway up the frame. Many imagers will often focus their efforts to frame up the trunk itself. It is a beautiful and worthy target, but without the surrounding context, it’s difficult to see as a “trunk”. A little girl at an outreach event once told me it looked like a mermaid sitting on a rock, and I can’t disagree. Another friend imaging the target presented it sideways, and my wife noted that it looked more like a dragon’s head. Now I can’t unsee it! A 40 light year long dragon’s head at that!
A one-shot color camera will capture the entire IC 1396 region or the trunk itself well enough. Better results will be had however using one of the many available tri-band light pollution filters that brings out the Ha (red) and OIII (blue) regions of emission targets particularly well. This is a target where a monochrome camera and filters will have some additional advantage though. The color images shown so far were taken with a monochrome sensor and RGB filters, combined with some Ha images. Ha (Hydrogen Alpha) captures the red light from glowing hydrogen gas in emission nebula and provides a great deal of additional detail that can then be combined with an RGB color image. Hydrogen Beta is also present in Ha regions in lesser concentrations, and many imagers will combine some Ha data with their red channel, and about 20% or so of the Ha image to their blue color channel to represent the blue light of Hydrogen Beta. I employ this technique myself most of the time. This region is also an ideal candidate for a full narrowband approach shown below.

This image which focuses on the trunk itself was taken with three narrowband filters, Hydrogen Alpha, Oxygen III, and Sulfur II -- the most common narrowband filters employed by amateur astrophotographers. These three monochrome channels are then mapped to RGB colors in such a way to not just provide some visual appeal, but also to highlight visually the concentrations of these three different elements in the nebula. The specific treatment above is called the “Hubble Palette”, as this particular color synthesis was first used for similar narrowband images from the Hubble Space Telescope. One of the biggest advantages to these narrowband wavelengths is they are quite resistant to light pollution, and even moonlight! This narrowband image was taken from a neighborhood backyard not far from the bright lights of Orlando Florida for example.

Like me, you probably do not have access to a space telescope, but as you can see here, space is still quite accessible from your own back yard, or a dark sky site. This month, there’s a giant space elephant flying around up there… or a dragon… or a mermaid. Go get it!

  • Name: The Elephant Trunk / SAC vdB 142/IC 1396A
  • Constellation: Cepheus
  • Classification: Dark Nebula
  • Distance: About 3,000 light years
  • Apparent Size: 45 Arc minutes
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