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Aug30-04, 06:54 PM
Sci Advisor
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At its closest, Jupiter is 4.2 AU away from Earth. It's 142,984 km gives it an angular diameter of about 47 arcseconds in our sky:

Magnified 200 times, it would have an angular size of about 2.6 degres, a little over 5 times the angular size of the Moon (0.5 degrees) viewed with the naked eye.

Saturn would be a little over a degree in angular size at the same magnification.

You should be able to see at least four of Jupiter's moons, along with several differently-colored cloud bands. The great red spot should be very obvious. On a good night, you should be able to see considerable detail in the regions where the cloud bands mix.

Saturn will appear five times smaller in the same eyepiece, but will easily show its rings. On a good night, the Cassini gap, the division between the inner and outer rings, should be quite easy to see. Several moons would be visible if you know where to look for them on the night in question. The planet may show some color gradations on the disc, but it is generally featureless.

Before buying a telescope, I strongly urge you to find a public star party in your area. Attend it and try out various kinds of telescopes. Ask the owners as many questions as you can. Choosing a telescope involves a lot more criteria than just the kind of detail it'll show on a planet!

- Warren