John B has alerted me to these questions on the Forum, which I am no longer reading.
As previous posters have noted, Jupiter and Saturn were in the southeastern sky on the nights over which the Rendlesham incident unfolded. For those who understand the astronomical brightness scale, Jupiter was at magnitude -2.0, which is brighter than Sirius, the brightest star in the sky, while Saturn was around mag +1, which is a bit brighter than the first-magnitude star Deneb.
At 3am on 1980 Dec 28, Jupiter and Saturn were at around 23 degrees altitude in the SE and still rising. An hour earlier they would have been at about 15 degrees altitude and an hour later at around 30 degrees.
Jupiter and Saturn were just over a degree apart, equivalent to two Moon widths.
None of these figures changed appreciably over the three nights of the incident.
Planetary movements are complex and there is no regularly repeating cycle. I don’t understand how this part of the question is relevant to the case. If you want to play around with a chart of planetary orbits see here
http://www.heavens-above.com/planets.aspx?
Does any of this matter? It’s possible that Jupiter and Saturn were among the lights in the sky seen by Col Halt and others but there is no clear evidence of this from the eyewitness descriptions so Jupiter and Saturn have never formed part of my explanation.
There were reports of starlike objects hovering over the forest for hours but these objects were at lower altitude than Jupiter and Saturn and in different directions. I have dealt with these reports at length here
http://www.ianridpath.com/ufo/rendlesham3.htmFor those who are not familiar with my explanation of the case, the original sighting of an object apparently crashing into the forest around 3 am on 1980 December 26 coincided with a bright fireball over southern England
http://www.ianridpath.com/ufo/rendlesham1d.htmIn their witness statements made for Col Halt, John B and Ed C admitted that after they had entered the woods they saw and chased an unidentified light that turned out to be the lighthouse, but this was not the original stimulus.
Ian