Centering the sun as it set?

On the 5th of June I recorded a few hours of the transit of venus. Now I am trying to create a time lapse video of the event, but need to find a way to keep the sun in center frame. As the sun set it drifted towards the lower right of the frame, at which time I would recenter the sun and let it record until it needed to be adjusted again. While doing this I was under the impression that I could somehow get iMovie to keep the sun in the center and I could then just fill the missing area of the frame with black since that is what it was in the first place with the filter I had in place.

Any ideas or suggestions, or if this is even possible is greatly appreciated. This is my first REAL project with iMovie so I am a bit over my head here! Thanks so much.

Dave W.