MARS
The planet that varies most in the beauty of its aspect is Mars. It is as much as fifty times brighter when it is nearest to us than it is at its greatest distance from us. At its brightest it is many times more brilliant than any of the first-magnitude stars; but when it leaves our neighborhood and goes far off into space in its journey around the sun, its glory is so dimmed that it becomes not brighter than an ordinary second-magnitude star, such as the pole-star, and less brilliant than the brightest stars in the Big Dipper.
These extreme changes of brightness are due not so much to any great distance that Mars goes from us in comparison with other planets as to its coming so very near to us at times. It is, after all, a small body, and no great distance, as heavenly distances go, is required to make it show so. But the eccentricity of its orbit brings it sometimes very near us, and its near approaches are at a time when we can see its entire disc, and not a mere crescent, such as we see when Venus is nearest to us. Mars does not come quite so near to us as Venus comes, but when he is in the best position to be seen he is much nearer than she is when in her best position. For we have seen that Venus is brightest before she reaches her nearest position to us, while Mars is brightest when he is at his nearest to us. When Venus is at greatest elongation she is three times farther away than Mars is at his nearest.
HOW TO IDENTIFY MARS
But with all his variations in brilliancy and beauty Mars remains ever a charming, rosy-hued planet, shining always with a steady, clear light, and when once we have come to know him is not easily mistaken for any other planet, or for any of the brilliant stars that may more or less resemble him in color. Red in varying degrees of intensity is, perhaps, the most obviously distinguishing mark of Mars; but his own characteristics are never more distinct than when his path takes him into the region of the two best-known red stars in the heavens. These are Antares, the glowing star in the constellation Scorpio, which we see in the southern sky during the summer, and ruddy Aldebaran, which shines in the head of Taurus and under the Pleiades through the bright wintry nights. On every journey around the skies Mars passes near these two stars. They are both in the constellations of the zodiac, and are often quite near to Mars, as well as to the other planets and the moon. The stars, though of the same color as Mars, are much more jewel-like than the planet. Mars is less sparkling. When it is small, it shows a placid, rosy little disc, without much gaiety, and not in any way suggesting anything martial; but at its largest, it has a distinctly flame-like aspect, which easily suggests why it was named for the god of war.
THE TWO PHASES OF MARS
We see its full face when it is opposite the sun. When half-way between opposition and conjunction it becomes gibbous, as shown in the photograph on the right. These photographs were made at the Mt. Wilson Observatory.
Mercury is the only planet that in color even suggests Mars, and for Mercury it can never be mistaken after one has once seen the two planets. Mercury, we know, is always very near the sun; but when visible at all is, even in that unfavorable situation, always as bright as a first-magnitude star. Mars is near the sun, to our view, only when it is approaching conjunction, and it is then so far from us that it always appears as a rather small star, and, while never insignificant, is, in this situation, quite inconspicuous even as compared with the rarely visible Mercury.
On seeing a planet, then, sufficiently high above the horizon to attract one’s attention, one may be sure that it is Mars if it is red, and equally sure that it is not Mars if it does not show this color. Under certain atmospheric conditions the sun, moon, and all the planets sometimes appear red when they are very near the horizon; but in this situation there is always something other than color that marks them.