Venus, Mars, Jupiter, and Saturn, brilliant beauties that they are,
have always been distinguished features of the heavenly view. The
records of Mercury do not go back so far as those of these more easily
seen planets, yet there is no reason to think that he has not been
always known, though less widely, perhaps, than the four planets more
frequently in view. To Uranus belongs the distinction of being the
first planet that was _discovered_--a distinction that one cannot help
but feel was too long delayed, for it did not come until 1781. For ages
and ages his lovely pale beams had been shining down upon us from his
little disc, no fainter in brilliancy than many a sixth-magnitude star
(a degree of brightness which we think is within the limit of good
vision, even in these days), and no human being had been conscious that
this bright body was only another member of the solar family, circling
with the rest of us around our parent, the sun, and having nothing in
common with the far-off stars among which we had numbered him. Nineteen
times he had been charted as a fixed star before his identity was
suspected, and after he became known to us as a planet he was, by means
of these charts, traced back for one hundred and thirty years, and much
information was thus gained concerning his orbit and movements.
Uranus was not, however, discovered through observation of his movement
among the stars. A view of his actual disc was caught by the musician
and astronomer, Herschel, as he gleaned with his telescope in that part
of the sky where the planet lay, one hundred and seventy-one years
after the invention of that aid to vision. It was at first thought that
a comet had been discovered, but later investigation showed a much more
important member of the solar system, and the discovery of a new planet
was announced.
George III. was then King of England, and the loyal Herschel called
the planet _Georgium Sidus_ in honor of that monarch. Fortunately,
the world-wide interest in this newly discovered body saved it from so
local an appellation, and it finally came to be called after Uranus,
the father of Saturn, a name somewhat more in keeping with its place
among the planets. In England, however, a very commendable loyalty to
Herschel has resulted in the planet’s sometimes being called Herschel,
after its discoverer, and we see this name often in English books on
astronomy, especially the older books; but Uranus is now the generally
accepted name.
The symbol of the planet as it appears in all almanacs--at least in
all English almanacs--is a capital H with a planet swinging from the
cross-bar in the letter, thus ♅. And to this extent the discovery of
the planet by Herschel is commemorated. In American almanacs the symbol
is contracted into this figure ♅.
It is a matter for regret that Uranus does not come more easily within
our view; for he is a very beautiful planet, pale green in color, and
unlike any of the others in his aspect. There are, however, very few
persons nowadays who can see him without the aid of at least a small
glass, and to most of us he must ever remain a body with which we can
have no personal acquaintance. None the less he must have an interest
to us such as attaches always to anything so closely related to us,
and sharing with us a common origin and a common destiny. To those who
have unusually keen vision--or a small telescope--there will be much
pleasure in viewing the planet. But even to those who have not these
facilities for seeing, it ought to be interesting to know in what
region of the skies this far-off member of our family dwells, what his
wanderings are, and something of his personality and habits.
It requires a few days more than eighty-four years for Uranus to make
one revolution around the sun, so that he moves even more slowly than
Saturn from one constellation to another; and if we could only see him
more easily, he would be scarcely more difficult to keep track of than
a fixed star. He remains in each constellation somewhere near seven
years and his change of place in the skies amounts in one year to but
little more than four degrees, which is less than the distance between
the pointers.
Since Uranus was discovered he has made one circuit of the skies, which
he finished in 1865, and he is now (1912) more than half-way around
on another. His position now is in Capricornus, nearly twenty degrees
east of the “milk dipper” in Sagittarius, and for the next quarter of a
century he can be seen by any who have eyes, or a glass, to accomplish
this during the summer evenings. Each year he will be about seven
degrees farther east. He is, however, still pretty far south of the
equator, and not so easily seen as he will be when he reaches that
part of the ecliptic which runs somewhat higher in the skies. Even an
opera-glass will bring Uranus into the view of many persons. His path
deviates very little from the line of the ecliptic--never quite so much
as half a degree. The knowledge of this makes it less difficult to find
him.
The synodic period of Uranus is about three hundred and sixty-nine
days, so that an opposition occurs about four or five days later each
year. He was in opposition this year (1912) on July 24th. In 1913 an
opposition will take place on July 29th, and in 1914 on August 2d, and
oppositions will occur about four days later each year thereafter.
Uranus is twice as far from the sun as Saturn is, and nineteen times
as far as the earth. Its mean distance from the sun is 1,784,732,000
miles, and at this distance more than two hours and a half would be
required for light to travel from the sun to the planet. Viewed from
the planet, the sun would appear only about two and a half times
larger than Jupiter appears to us, and the earth would be a very small
telescopic body, if, indeed, it would be visible at all. Even at this
great distance from the sun, and with the sun showing so small as it
does, the planet would still have more than a thousand times as much
light as we get from our moon, and so in this respect might be fairly
comfortably provided for even for eyes constructed like those of human
beings. The heat the sun’s radiant energy furnishes to Uranus is, from
our point of view, almost a negligible quantity. If there were no
other source of supply, the normal temperature of the planet would be
more than three hundred degrees below zero, Fahrenheit. There is no
reason to think, however, that this is the temperature that prevails on
Uranus. As far as we can tell, it has a dense and extensive atmosphere,
and probably very considerable internal heat.
Uranus is smaller than either Jupiter or Saturn; but it is much larger
than Mars, Venus, Mercury and the earth combined. Its diameter is
nearly thirty-three thousand miles. Its volume is sixty-five times
as great as that of the earth; but its mass is only about fourteen
times the mass of the earth, which shows it to be a very much expanded
body. It is slightly more dense than water, but only about two-tenths
as dense as the earth. Its force of gravity is small for so large a
body--only about nine-tenths that of the earth.
There is every indication that the planet is not a solid body at all,
and that it is, perhaps, largely vapor. We undoubtedly cannot see the
surface of it; but through the telescope it faintly shows the same
belted appearance that we see on Jupiter and on Saturn, though it is
difficult to see the belted region, which is near the equator, because
the axis of the planet is so inclined to its orbit that much of the
time the poles are pointed almost toward us. The spectroscope indicates
something of the same materials in its atmosphere that the other large
and faraway planets have, and there is no reason to doubt that the
planet is in a much earlier stage of development than any of the
terrestrial planets.
We really know nothing certainly about the rotation of Uranus; but
there seems to be some indication that, like Jupiter and Saturn, it
revolves swiftly--in perhaps ten or twelve hours, and hence has a very
short day and night. The great inclination of its axis must make its
seasons so abnormal, from our point of view, that it is difficult to
understand what they are. Moreover, the planet is, at this stage of its
development, so far from being a habitable body, for beings such as we
know anything about, that the subject of its seasons seems not very
important or interesting.
It seems but fitting that this vapory, pale green planet should have
satellites with the fairy names of Ariel, Umbriel, Titania, and Oberon.
One can forgive a good many utilitarian feats in nomenclature for
the sake of these charmingly appropriate names for the satellites of
Uranus. Titania and Oberon were discovered in 1787 by Herschel, the
discoverer of the planet. They are not very much farther from Uranus
than our moon is from us, and are easily seen with a telescope.
Titania, the nearer to Uranus and the larger, is probably about one
thousand miles in diameter; and Oberon is not very much smaller. In
1852 Umbriel and Ariel were discovered. They are both smaller and
nearer to Uranus than either of the two first discovered, and are seen
with considerable difficulty, because of their proximity to the larger
and brighter body of the planet. There is not, however, very much
difference between any of the four in real brightness.