Dimitris
For the black screen problem I use direct copy instead of rotation so I have a way around with an if.
It would be nice if you find why and correct it, no hurry...
Robert
I want to recomend a book for you to read - "Strata" by Terry Pratchet.
Its fiction, but has a very interesting point of view about "previous" and "later". It involves lots of stars of course.