POSSIBLE MAGNITUDE VARIATIONS OF SATURN'S SATELLITES
by K.E. Chilton, Planetary Coordinator
For many years it has been known that he magnitude of Iapetus, Saturn's outermost moon, is variable. Recent observations have indicated that some of the other moons may vary in brightness, too. (Refs. 1,2) This was pointed out in Planetary Bulletin No.9. However, observers were left ot their own devices to work out the positions of the satellites.
Like all celestial bodies, the moon appears to revolve around the Earth, once every 24 hours. This is caused by the rotation of the Earth. However, the moon revolves eastward in its orbit, ie: in the same direction as the Earth. Therefore, it takes a little longer for the earth to catch up, lengthening the apparent revolution to 24h 50m.
Published in the October 1970 National Newsletter. [PDF]
The Moon that Never Was (Maybe?)
After reading about the “Planet That Never Was” in the last issue of the NEWSLETTER, I thought that our readers might be interested in a satellite which was photographed 13 times near the turn of the century but has never been seen since. This was Themis, a supposed tenth moon of Saturn.