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Saturn is the showpiece of the sky. Apart from Jupiter, it
is by far the largest member of the Sun's family; even though it is so far from
the Sun (886,000,000 miles on average) it shines brightly, and even a modest
telescope will show its superb system of rings. Also on view will be some of
the remarkably interesting retinue of moons or satellites.
I have been asked many time what size telescope is needed to
see the Moons now that Saturn is at a reasonable height in the dawn sky. Here are the average magnitudes of Saturn's principal satellites.
There are 62 satellites altogether. One of them, Titan Mag 9.7, is of planetary size, and is visible with a 2-inch telescope. Of the
rest, Iapetus Mag 13, Rhea Mag 9.7, Dione Mag 10.6, and Tethys Mag 10.7 are moderately bright, but the others cannot be seen except with the help of
powerful instruments.
Mimas Mag 12 and Enceladus Mag 11.6 are distinctly elusive
(I find them difficult even with a 12-inch reflector), but are interesting
because they seem to be only about as dense as water.
Next, reckoning outward from Saturn, we come to Dione Mag
10.6, which is much more massive than Tethys. My own observations indicate that
it is a little brighter, but in any case a modest telescope will show both.
Rhea Mag 9.7 is further out, and larger, so that it is quite easy to see in a
small instrument.
Between the orbits of Titan and the next major satellite,
Iapetus, there is a wide gap. In this region Bond, in 1848, found a small moon,
Hyperion Mag 13, which is distinctly difficult to observe.
All the inner moons move practically in the plane of
Saturn's equator, which is the plane of the ring-system. Iapetus, however, has an
orbital tilt of more than 14 degrees. It is a long way from Saturn, and its movement’s
are relatively slow. But its main point of interest lies in the fact that it is
variable in brightness. When west of Saturn, it is conspicuous; my
observations indicate that it can become brighter than the 9th magnitude.
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