To do
this successfully, and without waste of time, it is necessary to
have an astronomical ephemeris for the year. All the observable
phenomena are there predicted for the convenience of observers.
Perhaps the most curious observation to be made is that of the
shadow of the satellite crossing the disk of Jupiter. The writer
has seen this perfectly with a six-inch telescope, and a much
smaller one would probably show it well. With a telescope of this
size, or a little larger, the satellites can be seen between us
and Jupiter. Sometimes they appear a little brighter than the
planet, and sometimes a little fainter.
Of the remaining large planets, Mercury, the inner one, and Uranus
and Neptune, the two outer ones, are of less interest than the
others to an amateur with a small telescope, because they are more
difficult to see. Mercury can, indeed, be observed with the
smallest instrument, but no physical configurations or changes
have ever been made out upon his surface. The question whether any
such can be observed is still an open one, which can be settled
only by long and careful scrutiny. A small telescope is almost as
good for this purpose as a large one, because the atmospheric
difficulties in the way of getting a good view of the planet
cannot be lessened by an increase of telescopic power.
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