When Venus appears in the sky she is not often mistaken for any other
planet. Among all the planets she is the most readily recognized and
the easiest to find. This is due largely to her extreme brilliancy and
a peculiar silvery appearance that none of the other planets have;
but also, in part, to her limited range in the sky, and her favorable
situation for observation. Unlike Mercury, she is far enough away from
the sun to be seen above the horizon for as much as three hours after
sunset, and is then sufficiently high in the heavens to be seen free
from the vapors of the atmosphere at the horizon. Yet, being one of the
inferior planets, with her orbit smaller and nearer the sun than that
of the earth, she can never get so far from the sun as to be at any
uncomfortable height for viewing, and hence, when she can be seen at
all, is always an obvious bit of brilliancy and a joy to the beholder.
She is never higher in the sky than forty-five degrees, which is
half-way between the horizon and the zenith, and is never farther away
from the sun than forty-eight degrees. One frequently sees a bright
planet higher up in the heavens than this; but it is never Venus nor
Mercury.
We first begin to notice Venus in the evening sky about six weeks after
she has passed superior conjunction. She is then very near the sun, and
sets a little less than half an hour after sundown. Evening by evening
she grows gradually brighter, mounts higher and higher in the sky and,
consequently, sets correspondingly later, until in a little more than
seven months after superior conjunction, and about six months after we
have begun to watch her, she reaches her greatest elongation east from
the sun. At that time she is usually somewhere near forty-five degrees
above the sun, and is a very lovely and conspicuous object in the
evening sky, setting a little more than three hours after sundown.
From this point she begins to travel back toward the sun, still
becoming brighter each evening, because she is really coming nearer to
us; and in about four or five weeks she attains the greatest brilliancy
that she will have as an evening star during the particular revolution
she is making. About twelve days after her brightest she will reach the
point where she seems to be stationary for a time. This is when she
is about to overtake us in our journey around the sun. After a short
pause she will move on gradually, her course among the stars then being
retrograde or westward; but what we most notice is that she is drawing
nearer to the sun, setting earlier each evening, and becoming more
and more difficult to see. At the end of about three weeks she is in
inferior conjunction, on a line between us and the sun, and invisible.
She has run her course as an evening star for nine and a half months,
and has been visible anywhere from seven to eight months, the time
of her invisibility depending upon the eye of the observer and the
conditions of situation and atmosphere.
A week or two later we shall find her a splendid morning star, rising
nearly an hour earlier than the sun. About three weeks thereafter she
will be at her brightest as a morning star, and will continue to be
very brilliant for some weeks. In about five more weeks she will have
reached her greatest elongation west of the sun, and will rise about
three hours and a half before dawn. Then she will begin to retrace her
path, moving eastward, growing smaller all the time as she goes farther
away from us, and showing a slower apparent movement, which gives one
an agreeable sense of a reluctant parting, until after a little more
than seven months she will have reached the sun and will again be in
superior conjunction. She has then been a morning star for nine and a
half months, and has been visible for about the same length of time
that she was when she shone as an evening star.
This is a brief outline of a typical journey of Venus through one
synodic revolution. She began one of these journeys on July 5, 1912,
being then in superior conjunction. During the autumn of this year and
the winter of 1912–13 she may be seen shining with great brilliancy
in the west at sunset, and a few hours thereafter. Early in November,
1912, she and Jupiter will both be in Scorpio, where they will approach
within two degrees of each other; and there is no doubt that their
presence will add much charm to that region of the sky during the
entire autumn.
About the middle of February, 1913, Venus will appear half-way up to
the zenith at sunset. She will then be at her greatest distance east
of the sun, and will be very bright; but, though a little nearer the
sun, she will be still brighter shortly after the middle of March. A
month later she will be invisible, and inferior conjunction will occur
on April 24th. During most of May and all of June and July she will
be a morning star, and her brilliant beauty will well repay an early
morning outlook. She will get back to superior conjunction on February
11, 1914, and in that year she will be in an ideal situation for us
to cultivate a more intimate acquaintance with her. From the latter
part of March to November, 1914, she will be the brightest star in the
western evening sky, and will do much to enhance the beauty of the
pleasant summer evenings of that year. The sturdy, red-faced Mars will
meet her on August 5th, a little more than a month before greatest
eastern elongation, and might almost kiss her pale cheek as they pass
within one-sixth of a degree of each other, a distance equal to less
than one-third of the diameter of the moon.
The next long period when Venus will shine as an evening star will
comprise the spring and early summer of 1916. She will be at her
greatest distance from the sun during the last week of April, and will
not pass from view until about the first of July. Then again she will
be an evening star, and so seen in the west during the autumn of 1917
and the winter of 1917–18, reaching greatest eastern elongation during
the first few days of December, 1917. Her next return to the evening
sky will be for the first eight months of 1919, and the next will be
for the winter of 1920–21 and the spring of 1921.
The synodic period of Venus is nearly five hundred and eighty-four
days, or a little more than one year and seven months. That is, the
planet returns to the same position with relation to the sun and
the earth at intervals of about that length. The intervals do vary,
however, as much as a week or more, owing to the various motions and
situations of the planet and the earth. But every eight years Venus and
the earth come around to almost exactly the same relative position with
each other and the sun and the stars, and thus the appearances of Venus
at the various seasons practically repeat themselves every eight years.
The full splendor that she is to offer us in the summer of 1914 will
be repeated in 1922, just as that of 1914 will but repeat that which
she showed in 1906. And in each of the intervening years she will have
again the same appearances that she had eight years before.
With the following table as a guide, the appearances of Venus can be
followed through a number of years with sufficient accuracy for any
but a close student of her movements. The exact dates of elongations
and conjunctions will vary a few days, but for at least two or three
multiples of eight years not enough to make any material difference in
her various aspects.
1913--1921--1929--1937
Greatest eastern elongation, February 12th. Inferior conjunction,
April 24th. Greatest western elongation, July 3d.
1914--1922--1930--1938
Superior conjunction, February 11th. Greatest eastern elongation,
September 17th. Inferior conjunction, November 27th.
1915--1923--1931
Greatest western elongation, February 8th. Superior conjunction,
September 14th.
1916--1924--1932
Greatest eastern elongation, April 26th. Inferior conjunction, July
5th. Greatest western elongation, September 14th.
1917--1925--1933
Superior conjunction, April 28th. Greatest eastern elongation,
December 2d.
1918--1926--1934
Inferior conjunction, February 11th. Greatest eastern elongation,
April 22d. Superior conjunction, November 25th.
1919--1927--1935
Greatest eastern elongation, July 6th. Inferior conjunction,
September 14th. Greatest western elongation, November 25th.
1920--1928
Superior conjunction, July 5th.
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.