If you've been photographing close-up colour images of Saturn & Jupiter (i.e. w/ DSLR & long lens/scope) you may have noticed the discs of the planets showing the effects of atmospheric dispersion. Here's a quick thread on how to tackle this with the free software Registax. [1/5]

Atmospheric dispersion is where reddish light from the planet is smeared downwards & bluer light is refracted upwards -- this causes a reddish lower limb & turquoise/blue upper limb to show on bright objects like planet discs. [2]

You can buy Atmospheric Dispersion Correctors (ADCs) to correct these unwanted effects before the light enters the camera (they essentially use prisms to recombine the smeared colours). But there's a rough workaround you can do with Registax that's free... [3]

You first need to save your raw image in a format Registax can use - I like to use lossless PNGs. Then open the image file and look for the 'RGB Align' button in the functions tab (which appears on the last 'Wavelet' page in the processing workflow). [4]

This will bring up a colour channels alignment tool that has a manual setting; it allows you to nudge the blue channel down & the red back up (assuming the bottom edge of your frame is ~parallel to the horizon). Here's a before & after GIF to show how well it works. HTH! :) [5]