What makes a good Planetary Telescope?

THE PLANETS ARE THE AMONG the most rewarding targets for backyard telescopes, but they can also be the most challenging. Although planetary observing is all but immune to the effects of light pollution, it is particularly sensitive to atmospheric turbulence — what astronomers refer to as ‘seeing’ — the principal enemy of telescope performance. Grappling with issues of optical design and thermal properties, aficionados strive for instruments optimised specifically for the task. In recent years, notions of what constitutes the best planetary telescope have embraced Voltaire's axiom “the perfect is the enemy of the good,” often with surprising results. Atmospheric limitations Historian and AS&T Contributing Editor William Sheehan once compared planetary observing to “watching a motion picture in which the camera is out of focus except for an occasional sharp frame thrown…