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TIL - Linux supports tilted monitors... apparently 22° is best
(www.tomshardware.com)
This is a most excellent place for technology news and articles.
Earth's axial tilt is 23.5°, COINCIDENCE? I DON'T THINK SO!!!
Seriously though, I'd be tempted to set it to 23.5° as a gag and tell everyone "Well, for full accuracy, you have to correct for the Earth's axial tilt..."
Keep in mind that the planet rotates, so the angle between the ecliptic and the screen has to be recalculated periodically with a cron job.
Should be easy to automate it completely with an arduino and a stepper motor.
For this I would use a servo, not a stepper.