In
the case of Mercury about 116 days on the average elapse between its
reappearances; in the case of Venus, about 584 days. The latter, for
instance, having become an evening star at the end of April, 1901, will
become an evening star again in December, 1902.
With the aid of the Nautical Almanac and the charts the amateur will
find no difficulty, after a little practise, in keeping track of any of
the planets.
In the back part of the Nautical Almanac will be found two pages headed
"Phenomena: Planetary Configurations." With the aid of these the student
can determine the position of the planets with respect to the sun and
the moon, and with respect to one another. The meaning of the various
symbols used in the tables will be found explained on a page facing the
calendar at the beginning of the book. From these tables, among other
things, the times of greatest elongation from the sun of the planets
Mercury and Venus can be found.
It may be added that only bright stars, and stars easily seen, are
included in the charts, and there will be no danger of mistaking any of
these stars for a planet, if the observer first carefully learns to
recognize their configurations. Neither Mars, Jupiter, nor Saturn ever
appears as faint as any of the stars, except those of the first
magnitude, included in the charts. Uranus and Neptune being invisible to
the naked eye--Uranus can occasionally be just glimpsed by a keen
eye--are too faint to be found without the aid of more effective
appliances.
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