Mars revolves round the Sun in 686d. 23h. 30m., at a mean distance of 141 million of miles, which the eccentricity of its orbit may increase to 154 millions or diminish to 128 millions. The planet’s apparent diameter varies between 4″ in conjunction and 30″ in opposition. Owing to the great eccentricity of the orbit the planet’s apparent diameter as seen from the Earth varies very much at different oppositions. The real diameter is rather more than 4000 miles.
In 1772 a German astronomer named Bode, of Berlin, drew attention to certain curious numerical relations subsisting between the distances of the various planets. This “law,” as it has been sometimes called, usually bears Bode’s name, though it was not he but J. D. Titius of Wittemberg who really first discovered it.
each of which (the second excepted) is double the preceding; adding to each of these numbers 4 we obtain—
which numbers approximately represent the distances of the planets from the sun expressed in radii of the Earth’s orbit. A little table will make the matter more clear.
Planets. Distance: Bode’s Law. True distance from Sun. Mercury 4 3.9 Venus 7 7.2 Earth 10 10.0 Mars 16 15.2 [Ceres] [28] [27.7] Jupiter 52 52.0 Saturn 100 95.4 [Uranus] [196] [191.8] [Neptune] [388] [300.0]
Bode having examined these relations and noticing the void between 16 and 52 (Ceres and the other minor planets, and Uranus and Neptune also, being then unknown) ventured to predict the discovery of new planets, and this idea stimulated him to organise a little company of astronomers to hunt for new planets. Before, however, this scheme was got into working order, Piazzi, director of the Observatory at Palermo, on January 1, 1801, noted an 8th magnitude star in Taurus, which on the next and succeeding nights he saw again, and found had moved. He observed the strange object for 6 weeks, when illness interrupted him. However he wrote letters announcing what he had seen, one of them to Bode himself; but this letter, though dated Jan. 24, did not reach Bode at Berlin, till March 20—a striking illustration of the state of the Postal service on the Continent less than 100 years ago. The new body, at first assumed to be a tailless comet, was eventually recognised to be a new planet; and the name of Ceres, the tutelary goddess of Sicily, was at Piazzi’s instance bestowed upon it.
