[18] The magnificent planet Saturn as captured by PL using his 14-inch Schmidt-
Cassegrain Telescope fitted with a high-frame-rate mono imaging camera. A set of RGB
imaging filters were used to capture three separate colour images which were then
combined using Photoshop to produce the final image you see here.The four so-called Galilean moons, Io, Europa, Ganymede and Callisto,
are bright enough that they can be seen through a steady pair of binoculars,
and make excellent targets to photograph. Their brightness is such that even
modest equipment can pick them up. As a bonus, as the four moons orbit
close to the equatorial plane of the planet and Jupiter’s tilt relative to the Sun
is quite small at just 3.1 degrees, it is also possible to see a whole host of
interesting interactions between them and Jupiter’s disc.
These interactions include transits of the moons in front of Jupiter,
occultations as they are hidden behind the planet, and eclipses as they enter
Jupiter’s shadow. The moons can also cast their own shadows on Jupiter’s
disc and these are quite easy to observe through even small scopes. On rare
occasions when the tilt angle of Jupiter is low, it’s also possible to see moons
passing in front of, or casting shadows over, one another.
For the sharpest moon overview images, a high-frame-rate camera
will produce the best results, but the telescope requirements here are
quite modest. A 3-inch refractor on a driven equatorial mount is capable of
producing a lovely image of Jupiter and its family of Galilean moons. The
technique which works best here is to produce two images – one optimized
for the planet’s disc, the other set to record the moons themselves. The
moons will appear indistinct or even absent in the first image while Jupiter
will appear over-exposed in the second.
Once you have both captures, they can be combined in a layer-based
graphics program such as Photoshop (commercial), Paint Shop Pro
(commercial) or GIMP (freeware). There are many ways to do this but one
is to layer the over-exposed Jupiter image on top of the surface-detail-18optimized one. Align both images, then carefully paint out the disc of Jupiter
in the over-exposed image using black. If the glare from the planet has
created a bright halo, this too can be removed by over-painting if required.
Once done, simply set the upper layer’s blend mode to lighten and the bright
moons will be joined by the planet’s disc from the layer below.
Next on our list, moving outward from the Sun, we come to what in our
view is not only the loveliest of all the planets, but the loveliest thing in the
entire sky.Saturn
In itself, Saturn's not too unlike Jupiter. It is smaller and its inner temperature
is lower. It certainly qualifies as a gas giant with a silicate core containing
rocky particles and an immense surround of gas – mainly hydrogen with a
good deal of helium. There is no solid surface to land on, and it is not easy to
decide where the atmosphere ends and the body begins.
Several spacecraft have visited – Pioneer 11 in 1979, then two Voyagers in
1980 and 1981, and the present Cassini probe, named after one of the best
early observers of the planet, Giovanni Cassini (1625–1712).
Cassini went into orbit around the planet, and at the time of writing, early
2012, it has already lasted for some years and there is as yet no end in sightAstronomer Book