The Planets and Minor Solar System Objects

Abstract

Seven planets — Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune — are angularly large enough to be seen as disks in small telescopes. Of these, Uranus and Neptune at best are only 4 and 2.5 seconds of arc across respectively, and so little or no detail can ever be seen on them. The four Galilean satellites of Jupiter — Io, Europa, Callisto and Ganymede — can just be seen to be non-point sources under the best observing conditions. The remaining tens of thousands of objects (Pluto, the Asteroids, Planetary Satellites etc.) appear star-like at all times. Thus observing the planets and other solar system objects involves similar procedures to observing the Moon (Chapter 4) in the case of the five planets out to Saturn, and to observing stars (Chapter 7) for all the remainder.