Simple, Digital Blink Comparator

How do we - or can we - find "new" or moving celestial objects in our digital astro images? Well, here is an idea for "a poor man's blink comparator" to play with:

A blink comparator is a fairly sophisticated and costly device with which one could could view and compare photographic plates of identical star fields exposed at different dates. After careful alignment of the plates these were alternately projected such that their immages were superimposed in a blinking manner. Any celestial object that had moved between the two dates of exposure would then reveal themselves by jumping forth and back to the eyes of the viewer, while any "new star" (nova or variable) would reveal itself as a blinking star at a fixed position.

Today, I assume, there are other digital means of comparing (digital) images, but one could in principle make a digital blink comaparator with simple animated gif. Again, take two shots at different times; align them in your photographic imaging software. Then crop them and use them for an animated gif image.

Now, I have never had the fortune to photograph a nova, but take the example below. In this shot of Orion, I have inserted an artifical "new star "in the image to the right. Can you see, where it is?



Not too easy - eh? But try clicking either picture and see what happens. Now, the "new star" (blinking) should be fairly easy to find. Granted, I have cheated and used the same exposure and you could eqaually well subract these images digitally from one another and find the star this way. But in real life, no two exposures are completely identical, and the fixed stars would hardly ever fully cancel out each other in a digital  subtraction. Anyway, now the idea has been presented for you to experiment with, if you  would like to.
Another, more real - albeit very simple example is presented below. This shows the slight movement of planet Saturn in southern Leo during three weeks in April 2009:
Saturn in Leo, April 2009

Four photos taken on 2, 10, 15 and 22 April 2009 added. All individual frames are 8 second exposures at ISO 320 captured with Olympus C50 Zoom digital camera with 7.8 mm focal length, f/2.8

Images are slightly contrast enhanced, aligned, cropped and added in PhotoImapct12.

The pinkish background colour is just what it looks like: Light pollution added up!

Clik on Image to see an animation in the "Digital Blink Comparator"




Copyright 2009 - Steen G. Bruun