A High Reflecting Power

The density of Uranus is only about one and one-fourth times that of water, so that a body at its surface, weighing 100 pounds on the earth, would weigh only 90 pounds on Uranus. Although Uranus is the brightest of the three discovered planets, it cannot be found unless one knows exactly where to look for it, as it appears without the aid of a telescope only as a star-like object of fifth or sixth magnitude and near the limit of visibility to unaided vision. Uranus has a high reflecting power, which implies that its atmosphere is cloud-filled; and the presence of faint belts, similar to those on Jupiter and Saturn, have been detected. It is believed that it has a dense and extensive atmosphere. The rotation of the planet has been found, spectroscopically, to have a period of ten and three-fours hours. Uranus has four remarkable satellites, the brightest not exceeding 1000 miles in diameter. They are, with several faint satellites of Jupiter and Saturn, the faintest objects to be observed telescopically in the solar system.

The two brightest, named Oberon and Titania, were also discovered by Sir William Herschel; the other two, Ariel, nearest the planet, and Umbriel, were not found until 1851, by Lassell. The brightest are of the 14th magnitude, and they can only be detected with a 10-inch telescope under good observational conditions. The strange fact about these satellites is that the plane of their orbits is inclined nearly perpendicularly to the ecliptic, and in that plane they revolve backward, or from east or west. The equator of the planet lies almost in the same plane as the satellites, and the direction of rotation of the planet is also from east to west, which is contrary to the usual direction of motion in the solar system.

It was not long after the discovery of Uranus before it was found that the planet was perturbed in its motion by some unseen body. This disturbance finally reached what was regarded by astronomers as the "intolerable" amount of two minutes of arc, which is so great as to be almost visible to the eye without telescopic aid. Two young mathematicians, Adams of England and Leverrier of France, were working on the problem mathematically in the year 1846. Adams presented his results to the Astronomer Royal of England before Leverrier wrote his memorable letter to Galle at the Berlin Observatory, telling him to point his telescope to a certain position in Aquarius and he would find, within a degree of that point, a new planet looking like a star of the ninth magnitude but with a perceptible disk.

Fate favored Leverrier rather than Adams, for Galle was in possession of a new star chart covering that region. This greatly aided the search, and within half an hour of the time the search was begun the planet was found as predicted.

By: davidbunch

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