The Ways of the Planets

by Martha Evans Martin

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.