The meetings of Venus with the other planets do not, however, occur
with this delightful regularity. They all are moving about in their own
ways, and engaged in their own affairs, and only the earth gets back
to repeat the meeting with her in just eight years. These eight-year
cycles are due to the fact that Venus makes thirteen revolutions
around the sun while the earth makes eight. Her journey around the
sun requires a little less than two hundred and twenty-five days
(224.70), and the earth completes its revolution in a little more than
three hundred and sixty-five days (365.25). So at the end of about
two thousand nine hundred and twenty-two days--which equals eight
years--they come into almost exactly the same relative positions in
their orbits with which they started out, and begin the cycle anew.
DISTANCE AND BRILLIANCY
The mean distance of Venus from the sun is 67,269,000 miles. Her orbit
more nearly approaches the form of a circle than that of any other
planet. It is, like the orbits of the other planets, an ellipse, but
of such small eccentricity that the difference between her greatest
and least distance from the sun is scarcely more than a million miles.
Light, traveling as it does, at the rate of a little more than one
hundred and eighty-six thousand miles a second, goes from the sun to
Venus in about six minutes. It takes something more than eight minutes
for light-rays to come from the sun to us. When Venus is nearest the
earth, her silvery beams come swiftly across to us in a little more
than two minutes. When she is farthest from us, the rays of light
require a few seconds more than fourteen minutes to travel over the
distance. She is, when at her greatest distance, more than one hundred
and thirty-five million miles farther from us than when at her nearest.
This difference is due not to any great eccentricity in her orbit, or
in that of the earth, such as causes Mercury’s great variations of
distance, but to the situation of the two bodies in their orbits: they
are nearest together when they are on the same side of the sun, and
farthest apart when on opposite sides.
Usually at inferior conjunction Venus is a little more than twenty-five
million miles from the earth. At her nearest possible approach to us,
however, which takes place at inferior conjunction, when the earth
is nearest the sun and Venus is farthest from it, a situation which
occurs only once or twice in a century, the distance between us and
the planet is only a little more than twenty-three million miles. This
is nearer than any other heavenly body ever approaches us, except the
moon and, so far as we now know, one small asteroid. Also, it is nearer
than Venus comes to any other heavenly body except perhaps Mercury.
Her nearest approach to that planet is also about twenty-three million
miles.
Public-domain text, read in full here on John Shaqi.
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