You will have no difficulty in recognizing Venus, but you must choose
the right time to look out for her. In the first place, you need never
expect to see Venus very late at night. You should look for the planet
in the evening, as soon as it is dark, towards the west, or in the
morning, a little before sunrise, towards the east. I do not, however,
say that you can always see Venus, either before sunrise or after
sunset. In fact, for a large part of the year, this planet is not to be
seen at all. You should therefore consult the almanac, and unless you
find that Venus is stated to be an evening star or a morning star, you
need not trouble to search for it. I may, however, tell you that Venus
can never be an evening star and a morning star at the same time. If
you can see it this evening after sundown, there is no use in getting
up early in the morning to look out for it again. The planet will
remain for several weeks a splendid object after sunset, and then will
gradually disappear from the west, and in a couple of months later will
be the morning star in the east. Venus requires a year and seven months
to run through her changes, so that if you find her a bright evening
star to-night, you may feel sure that she was a bright evening star a
year and seven months ago, and that she will be a bright evening star
in a year and seven months to come. Nor must you ever expect to see her
right overhead; she is always to the west or to the east.
The splendor of Venus, when at her best, will prevent you at such times
from mistaking this planet for an ordinary star. She is then more than
twenty times as bright as any star in the heavens. The most conclusive
proof of the unrivalled brightness of Venus is found in the fact that
she can be recognized in broad daylight without a telescope. Even on
the brightest June afternoons the lovely planet is sometimes to be
discerned like a morsel of white cloud on the perfect azure of the sky.
Venus is so brilliant that perhaps you will hardly credit me when I
tell you that she has no more light of her own than has a stone or a
handful of earth, or a button. Is it possible that this is the case,
you will say, for as we see the planet so exquisitely beautiful, how
can she be merely a huge stone high up in the heavens? The fact is that
Venus shines by light not her own, but by light which falls upon her
from the sun. She is lighted up just as the moon, or just as our own
earth is lighted. Her radiance merely arises from the sunbeams which
fall upon her. It seems at first surprising that mere sunbeams on the
planet can give her the brilliancy that is sometimes so attractive.
Let me show you an illustration which will, I trust, convince you that
sunbeams will be adequate even for the glory of Venus.
Here is a button. I hang it by a piece of fine thread, and when I
dip it into the beam from the electric lamp, look at the brilliancy
with which the mimic planet glitters. You cannot see the shape of the
button; it is too small for that; you merely see it as a brilliant gem,
radiating light all around. Therefore, we need not be surprised to
learn that the brilliancy of the evening star is borrowed from the sun,
and that if, while we are looking at the planet in the evening, the sun
were to be suddenly extinguished, the planet would also vanish from
view, though the stars would shine as before.
Thus we explain the appearance of Venus. The evening star is a
beautiful, luminous point, but it has no shape which can be discerned
with the unaided eye. When, however, the telescope is turned towards
Venus we have the delightful spectacle of a tiny moon, which goes
through its phases just as does our own satellite. When first seen as
an evening star Venus will often be like the moon at the quarter, and
then it will pass to the crescent shape. Then the crescent becomes
gradually thinner, and next will follow a brief period of invisibility
before the appearance of Venus as the morning star. It seems at first
a little strange that Venus when brightest should not be full like the
moon, which in similar circumstances is, of course, a complete circle
of light. The planet, however, has a very marked crescent-shaped form
in these circumstances. But at this time the planet is so near us
that the gain of brilliancy from the diminution of distance more than
compensates for the small part of the illuminated side which is turned
towards us.
You ought all to try to get some one to show you Venus through a
telescope. A very large instrument is not necessary, and I feel sure
you will be delighted to see the beautiful moon-shaped planet. You will
then have no difficulty in understanding how the brightness of the
planet has come from the sun. The changes in the crescent merely depend
upon the proportion of the illuminated side which is turned towards us.
Were Venus itself a sunlike body we should, of course, see no crescent,
but only a bright circle of light.
In Fig. 50 you will notice an imaginary picture of a young astronomer
surveying Venus with a telescope. I have not, as is obvious, attempted
to show the different objects in their proper proportions. The sun is
supposed to have set, so that his beams do not reach the astronomer.
Night has begun at his observatory; but the sunbeams fall on Venus,
and light her up on that side turned towards the sun. A part of this
lighted side is, of course, seen by the telescope which the astronomer
is using, and thus the planet seems to him like a crescent of light.
[Illustration: FIG. 50.--To show that Venus shines by Sunlight.]