image stacking for astrophotography

src/astronomy/astrophotography/image_stacking.md

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+# Image Stacking
+
+Image stacking is the process of combining multiple images of the same thing into a single image. This is done for multiple reasons - to increase dynamic range, to reduce the effects of noise, etc. 
+
+## Theory
+
+[Keith Wiley](https://keithwiley.com/astroPhotography/imageStacking.shtml) has a really good article on the theory behind image stacking.