Up to our north in the constellation Cepheus, the king, lies a cloud of gas and dust 100 light-years wide known as IC 1396. Within this region are large, denser globules of dust that serve as the birthing grounds of new stars. One of them is IC1396A, also known as the Elephant Trunk Nebula, thanks to its distinctive shape. This long column of dust, which is the central feature of the above image, is around 25 light-years tall. At a distance of 2,400 light-years, the portion of the nebula seen in the image spans about 55 light-years by 38 light-years.
The cloud’s gas glows as a result of the intense radiation from the star system HD206267A, which lies just off the top of the frame of the image. This star system contains two massive, extremely luminous O-type stars that orbit each other in a mere 3.7 days. A third star of similar luminosity and temperature may be an additional companion to the other two, though it is uncertain if it is gravitationally linked to its neighbors. The particles streaming off the stars (the stellar wind) are exceptionally high even for the hottest stars – over 3,000 km/s. The wind helps to erode away the surrounding cloud, including the dustier portions that contain developing nascent stars. At the top of the Elephant Trunk is a small cavity in which two stars can be seen. The cavity may have been produced by the stars as they grew and started producing their own stellar winds.
The image above is a false-color view of the nebula and is a combination of three images, each assigned a specific color of either red, green, or blue, and a luminance image that adds in information about brightness. The “red” image was made by combining multiple exposures obtained with a filter that only lets through the red light of sulfur atoms. In all, the 60 digitally stacked five-minute exposures produced a final red image with an effective exposure of five hours. The same was done to make the green and blue images, but with filters that only permitted through the red light of hydrogen and blue-green light of oxygen atoms, respectively. These images are known as “narrowband” images because the filters only transmitted extremely narrow slices of the full rainbow of colors. Though very useful for scientific work, they are also particularly useful for light-polluted areas as the filters reject much of the ambient light pollution while still letting through the light produced by the nebula. After combining the three color frames, a five-hour luminance exposure, which used no filters, was added to increase the brightness detail in the final image. Thus, the featured image is 20 hours of exposures. Though this may seem like a very long time, astrophotographers can easily render photographs from hundreds of hours of exposures!