Use the recent "Astronomy Picture of the Day" by NASA as your desktop wallpaper (Python script for Mac OS X, should be easy do adapt for Linux or Windows)
To install run the following command in your terminal:
cd <change_wallpaper_dir>
bash INSTALL.shThis will create the folder specified to save APOD images, update all paths needed by the change_wallpaper script, and create a symlink to the io.brocklobsta.changewallpaper.pist in ~/Library/LaunchAgents.
To stop this service from running periodically execute the following command:
mv ~/Library/LaunchAgents/io.brocklobsta.changewallpaper.plist ~/.TrashNote: This will not delete any saved pictures.