My plan was simple — over a period of number of days, take a picture of the sky where my telescope thought Neptune would be, stack the images, and find a line of dots against the fixed stars. Didn’t work.
There are 4 sub-images (“subs”, in the lingo), taken on 09/15, 09/21, 10/03, and 10/10. 25 days.
Here’s the partially processed stack, straight from the computer. Note that you select one of the subs as a reference, then try to fit the others on top. This is a full frame, 3.5×2.5 degrees in the sky:
I find this image aesthetically pleasing, though it is disconcerting that the 4 subs were so far from alignment. Somehow I thought the tracking software in my rig would do a better job. But in any case… Neptune takes 165 years to make a trip around the sun — 360 degrees in 165 years, or about 2.2 degrees a year. That’s about .006 degrees a day, or around 20″/day, on average, or an arcminute every 3 days. So, maybe 6-7 minutes over 25 days? A little less than half a cm on my screen, that would be.
Because of Earth’s motion around the sun, Neptune stops, then goes retrograde for a while, every year, and I don’t know where we are in this cycle. So maybe it didn’t move at all. I could probably get Stellarium to show me, but for the time being I’ll chalk it up as a failed experiment that gave me a pretty picture.