On rare occasions, when Venus is in inferior conjunction, she makes a
transit, and can then be seen as a black dot moving over the bright
face of the sun. Transits can occur only when the earth and the planet
are near the point where their orbits cross each other. The earth is at
this point every year on June 7th and December 7th; but the orbit of
Venus is such that she is there on the proper dates only four times in
a period of two hundred and forty-three years. In every two hundred and
forty-three years four transits take place. They occur in pairs, eight
years apart, and in the same month. If a pair occur in June, it will be
one hundred and five and one-half years after the last one of the pair
until we have the first of the December pair of transits. After that it
will be one hundred and twenty-one and a half years until we have the
first of another pair of June transits.
The first transit of Venus that was scientifically observed was in
December, 1639. It was the last of a December pair, there having been
a transit eight years before, in December, 1631. One hundred and
twenty-one and a half years later, in 1761, a June transit occurred,
and in 1769 another one took place in June. Then there were no more for
one hundred and five and one-half years, when we had a December pair in
1874 and 1882. The next ones will be in June, 2004 and 2012.
Great importance was attached to those transits that occurred in 1874
and 1882, because they were expected to be useful in determining with
greater exactness the distance of the sun. Extensive preparations
were made for scientific observation of them; but the results were not
satisfactory, largely because the atmosphere of Venus prevented her
from showing a sharp outline at the moment of entering upon and of
leaving the face of the sun. The main scientific value of a transit of
Venus now is in the opportunity it may offer to investigate the nature
of her atmosphere. Even though that interesting question may have been
practically settled before another transit takes place, it will be
important to know to what degree the phenomena observed at the next
transit confirm the decision.
* * * * *
On account of the surpassing brilliancy of Venus, the brightest of all
the heavenly bodies after the sun and moon, she was to the ancients
the most important of all the stars and planets. She was the supreme
evening and morning star. As evening star she was known as Hesperus, or
Vesper; as a morning star she was called Phosphorus, or Lucifer, and
under all these names she is frequently mentioned in Greek and Latin
and kindred literatures.
The symbol of Venus is ♀, a figure which is nothing more than the
conventionalized form of a looking-glass, an article that is often
pictured in the hands of the goddess for whom our beautiful planet was
named. In her general aspect she is as placidly splendid and charming
as ever a goddess could be, and it is not strange that the happy ears
that could hear such strains should find her, as they did, singing a
rich contralto in the music of the spheres. Jupiter and Saturn, under
this mythological apportionment, sang bass, Mars took care of the tenor
strains, and the high soprano was carried by our little dwarf Mercury.