MARS

, one of the seven primary planets now known, and the first of the four superior ones, being placed immediately next above the earth. It is usually denoted by this character <*>, being a mark rudely formed from a man holding a spear protruded, representing the god of war of the same name.

The mean distance of Mars from the sun, is 1524 of those parts, of which the distance of the earth from the sun is 1000; his excentricity 141; and his real distance 145 millions of miles. The inclination of his orbit to the plane of the ecliptic, is 1° 52′; the length of his year, or the period of one revolution about the sun, is 686 23/24 of our days, or 667 3/4 of his own days, which are 40 minutes longer than ours, the revolution on his axis being performed in 24 hours 40 minutes. His mean diameter is 4444 miles; and the same seen from the sun is 11″: the inclination of the axis to his orbit 0° 0′; the inclination of his orbit to the ecliptic 1° 52′; place of the aphelion <*> 0° 32′; place of his ascending node <*> 17° 17′; and his parallax, according to Dr. Hook and Mr. Flamsteed, is scarce 30 seconds.

Dr. Hook, in 1665, observed several spots in Mars; which having a motion, he concluded the planet turned round its centre. In 1666, M. Cassini observed several spots in the two faces or hemispheres of Mars, which he found made one revolution in 24hours 40minutes. These observations were repeated in 1670, and confirmed by Miraldi in 1704, and 1719: whence both the motion and period, or natural day, of that planet, were determined.

In the Philos. Trans. for 1781, Mr. Herschel gave a series of observations on the rotation of this planet about its axis, from which he concluded that one mean sidereal rotation was between 24 h. 39 m. 5 sec. and 24 h. 39 m. 22 sec.; and in the Philos. Trans. for 1784, is given a paper by the same gentleman, on the remarkable appearances at the polar regions of the planet Mars, the inclination of its axis, the position of its poles, and its spheroidical figure; with a few hints relating to its real diameter and atmosphere, deduced from| his observations taken from the year 1777 to 1783 inclusively. He observed several remarkable bright spots near both poles, which had some small motion; and the results of his observations are as follow; viz,

“Inclination of axis to the ecliptic, 59° 22′.

The node of the axis is in <*> 17° 47′.

Obliquity of the planet's ecliptic 28° 42′.

The point Aries on Mars's ecliptic answers to our <*> 19° 28′.

The figure of Mars is that of an oblate spheroid, whose equatorial diameter is to the polar one, as 1355 to 1272, or as 16 to 15 nearly.

The equatorial diameter of Mars, reduced to the mean distance of the earth from the sun, is 9′ 8‴.

And the planet has a considerable, but moderate atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to ours.”

Mars always appears with a ruddy troubled light; owing, it is supposed, to the nature of his atmosphere, through which the light passes.

In the acronical rising of this planet, or when in opposition to the sun, it is five times nearer to us than when in conjunction with him; and so appears much larger and brighter than at other times.

Mars, having his light from the sun, and revolving round it, has an increase and decrease like the moon: it may also be observed almost bisected, when in the quadratures, or in perigæon; but is never seen cornicular, as the inferior planets. All which shews both that his orbit includes that of the earth within it, and that he shines not by his own light.