Tuesday, 9 April 2013

Some Pictures of Galaxies

I've recently been trying to get some really nice pictures of galaxies by stacking together multiple exposures from the BRT. I'd like to share two that I have made so far.

I know a lot of the people who get the most use out of the telescope are doing research of one kind or another: either doing variable star measurements or looking for supernovae are the usual topics. I think there is a lot to be said for the BRT's capabilities for astrophotography though.

Usually, to get a really beautiful picture of space would require perhaps hours of exposure (at least on the size of telescope we have). We limit people to 3 minutes of exposure per request to make sure everyone can have a go, but that doesn't mean you can't get some quite stunning results. The way to do it is to take a large number of pictures and then stack them together.

Stacking is where you combine multiple images to make a single image by averaging the pixels of all the images. So, the top left pixel of the resulting image is an average of the top left pixels on all the individual images and so on. The reason behind this is to reduce the amount of noise. 
All cameras produce some noise (some more than others). You often wont notice this in your pictures on your digital cameras because the light from the scene you are photographing is much brighter than the small amounts of noise added in your camera. On pictures of space though, the things you are imaging are extremely faint. Even though our CCDs produce far less noise than a digital camera, there is so little light coming from far away galaxies etc. that the noise can be quite noticeable.
The nice thing about noise is that it is random and that gives us a way to fix it. If you take enough images of the same object, in some of those images a particular pixel my be brighter than it should be. In others maybe darker. As you average them all, these start to cancel out and the speckled noise just becomes an even glow that can easily be removed, just leaving a crystal clear picture. The same is achieved by having a longer exposure time too.

The following two pictures are ones I have produced purely from BRT images that were returned to me over the course of about a week. They were assembled using the new fits viewer I mentioned in my previous post. Each one represents a total of over an hour of exposure (details beneath).

 Luminance: 10x3min clear
 Colour: 3x3min each of BVR (27 mins total)
 Pink Highlights: 10x3min H-alpha

 Luminance: 5x3min clear
 Colour: 3x3min each of BVR (27 mins total)
 Pink Highlights: 5x3min H-alpha