This planet being half as far again from the sun as our earth is, his light and heat are not half so much as our own. When in opposition to the sun, he is found to be five times nearer to us than when in conjunction; and, therefore, he appears so much bigger and brighter at one time than another. In 1719, his apparent magnitude and brightness were so much increased, that, by the uninformed, he was taken for a new star.
The telescopic appearance of Mars is very variable. This planet exhibits larger and more remarkable spots than any of the others. The belts and cloudy appearances are found to change their shape and arrangement frequently. The predominant brightness of the polar regions leads to the supposition that those parts of his surface, like the poles of the earth, are intensely frozen, or always covered with snow; and Dr. Herschell imagines that the changes in brightness are connected with the summer and winter seasons on that planet. The phases of Mars were first discovered by Galileo. Having his light from the sun, and revolving round it, he has an increase and decrease like the moon. At his quadratures, he appears gibbous, but never horned, like Venus, Mercury, and the Moon; which shows, that his orbit includes that of the earth, and that it is from the sun that he receives his light.
Between the orbit of Mars and that of Jupiter, the smaller planetary bodies, lately discovered, revolve. Ceres was discovered on the 1st of January, 1801, by M. Piazzi, astronomer at Palermo, in the island of Sicily. When viewed through a good telescope, it is of a ruddy color, appears to be of the size of a star of the eighth magnitude, and surrounded with a dense atmosphere. Her mean distance from the sun is 260,000,000 miles; and her revolution is performed in 4 years, 7 months, 10 days. Dr. Herschell and Schroëter differ very much as to the magnitude of this planet; the former says the diameter is only 160 miles, but the latter makes it more than ten times greater, or 1,624 miles. Pallas was discovered on the 28th of March, 1802, by Dr. Olbers, of Bremen. Its mean distance from the sun 270,000,000 miles; its diameter 80 miles; and it performs its revolution in about 4 years, 280 days. Juno was discovered on the 1st of September, 1804, by M. Harding, of Lilienthal. Its mean distance from the sun is 290,000,000 miles; and its diameter is 119 miles, and the time of revolution round the sun 5 years, 181 days. Vesta was discovered by Dr. Olbers, on the 29th of March, 1807. It is nearer to Mars than either of the other newly discovered planets; and the revolution through its orbit is performed in less time. The size of this planet is not known. Its light is more intense, pure, and white, than any of the other three.
A century and half ago it was conjectured, says a very intelligent author, that there must be a planet between the orbits of Jupiter and Mars, on account of the distance subsisting between those two planets. The discovery of Ceres confirmed this happy conjecture; but the opinion which it seemed to establish respecting the harmony of the solar system, appeared to be completely overturned by the discovery of Pallas and Juno. Dr. Olbers, willing to find a theory that should account for the facts newly ascertained, imagined that these small celestial bodies were merely the fragments of a larger planet, which had burst asunder by some internal convulsion, and that several more might yet be discovered between the orbits of Mars and Jupiter. He therefore concluded, that though the orbits of all these fragments might be differently inclined to the ecliptic, yet, as they must have all diverged from the same point, they ought to have two common points of re-union, or two nodes in opposite regions of the heavens, through which all the planetary fragments must sooner or later pass. One of these nodes Dr. Olbers found to be in Virgo, and the other in the Whale; and it was actually in the latter of these regions that M. Harding discovered the planet Juno. With the intention, therefore, of detecting other fragments of the supposed planet, Dr. Olbers examined, thrice every year, all the little stars in the opposite constellation of the Virgin and the Whale, till his labors were crowned with success, by the discovery of a new planet in the constellation of Virgo, to which he gave the name of Vesta.
The existence of four planets between the orbits of Mars and Jupiter, (continues the same author,) revolving round the sun at nearly the same distances, and differing from all the other planets in their diminutive size, and in the form and position of their orbits, is acknowledged to be one of the most singular phenomena in the history of astronomy. The discordance of these phenomena with the regularity of the planetary distances, and with the general harmony of the system, naturally suggests the opinion, that the inequalities in this part of the system were produced by some great convulsion, and that the four planets, as we have already hinted, are the fragments of a large celestial body, which once existed between Mars and Jupiter. To suppose them independent planets, as they must necessarily be if they did not originally form one, their diminutive size, the great eccentricity and inclination of their orbits, and their numerous intersections, when projected on the plane of the ecliptic, are phenomena absolutely inexplicable on every principle of science, and subversive of that harmony and order which before the discovery of these bodies, seemed to pervade the planetary system. Admitting, however, the hypothesis that these planetary bodies, are the remains of a larger body, which circulated round the sun, nearly in the orbit of the greatest fragment, the system resumes its order, and we discover a regular procession in the distances of the planets, and a general harmony in the form and position of their orbits. But, independently of analogical reasoning, the elements of the new planets furnish several direct arguments, drawn from the eccentricity and inclination of their orbits, and from the position of their perihelia and nodes; and all concurring to show, that the four new planets have diverged from one point, and have, therefore, been originally combined in a larger body.
Jupiter is the largest of all the planetary bodies, and, next to Venus the brightest. He was called by the Greeks Ζευς, which is from ζεω, to be hot, or, says Parkhurst, immediately from the Hebrew זי to shine, compounded, perhaps, with יש substance, q.d. the shining substance; a name very justly given to this planet, on account of his strong and clear light.
——“In distant skies
Revolves the mighty magnitude of Jove,
With kingly state, the rival of the sun.”
His mean distance from the sun is 490,000,000 miles, and his diameter is 89,170 miles, or more than 11 times that of the earth, and therefore his magnitude is 1,400 times greater than our earth; of course, as the surface of a globe increases according to the square of its diameter, our earth will, to the inhabitants of Jupiter, appear 121 times less than this noble planet appears to us. His revolution round the sun, from east to west, is performed in 11 years, 315 days, 14 hours, 39 minutes, 2 seconds, which is nearly twelve of our years; and his motion in his orbit is 29,000 miles an hour. He performs his diurnal rotation upon his axis in 9 hours, 55 minutes, 33 seconds, by which motion his equatorial parts are carried round at the amazing rate of 26,000 miles an hour, which is about twenty-five times the velocity of the like parts of our earth. He has, of course, a rapid succession of days, as the poet observes,