North America Nebula (Narrowband)

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The North America Nebula, shot in Narrowband(False Colour)


Annotated Version:

About the image:

This image is a false colour narrowband image shot on the ZWO ASI 294 MM Pro Cooled astronomy camera using Antlia 3nanometer filters for Ha (Ionised Hydrogen), Sii (Ionised Sulphur) and Oiii (Ionised Oxygen), shot over 3 nights from a Bortle 6 zone at F5.9, comprises a total of 12.4 hours of data. There are several named nebulae within this image. In the centre of the image is The North American Nebula, which is an emission nebula. It can be found fairly close to the star Deneb (see star chart below). Towards the centre bottom of the image is a small nebulous cloud known as the Pelican Nebula.


Within the North American Nebula is a prominent structure known as The Cygnus Wall, which I am currently shooting so check back soon for an update. This is the m shaped structure just slightly up and left from the centre of the image.


The whole north american nebula is approximately 140 light years across. Because it is an emission nebula, it is literally glowing in space, with the gases being ionised by a very hot star, believed to be the star named J205551.3+435225, estimated to have a temperature of over 40,000 Kelvin - to put that in perspective, our own sun is only 5,778 Kelvin. Narrow band data = Wide range of processing options + Starless Due to the nature of Narrowband imaging, unlike true colour RGB imaging, the three main elements that are captured - Hydrogen, Sulphur and Oxygen, are not red green and blue. Hydrogen is a Deep Red, Sulphur is a slightly deeper red, and Oxygen is a teal / greenblue colour. These are then combined into a final colour image but it gives freedom to how they are combined. There is the traditional SHO pallet (Sulpher = Red, Hydrogen = Green, Oxygen = Blue) which is used by Nasa for narrowband image produced by the Hubble Space Telescope. But there are other combinations as well. The image at the top of this page is created using Forax, which is a combination of SHO and HOO and some other combinations. The versions below is more akin to HOO pallet but does include all three datasets. The actual equations for each colour channel are as follows:

Red: iif(Sii > .1, Sii, (Ha*.7)) Green: iif(Ha > 0.7, 1-(1-Oiii)*(1-(Ha-0.3)), Oiii *(Ha+0.7)) Blue: iif(Oiii > .1, Oiii, (Ha*.3)+(Oiii*.2))

The second of these versions is a starless version. By using a form a neural net processing it is possible to remove the stars from the image so that the nebula structure becomes the entire focus of the image. Click on each of the images to view full size.

Where in the sky is it?

The North america nebula is located in the constellation of Cygnus, close by to the bright star Deneb.