Flowers of the Sky

by Richard A. Proctor

It will be noticed that Mars described a wide loop ranging to a considerable distance from the ecliptic (or sun's track). Saturn, on the other hand, travelled on a narrow and shorter loop lying much nearer to the ecliptic, his whole track, except just where he was turning,—his stationary points,—lying nearly parallel to the ecliptic. It may be well to mention the reason of this well-marked difference. Mars does not in reality range even quite so widely from the plane of the ecliptic as Saturn does. Nay, his path is even less inclined to the ecliptic. (This may sound like repetition, but the inclination of a planet's path to the ecliptic is one thing, the range of the planet north and south of the ecliptic, in miles, is another. Mercury, for example, has of all planets the path most inclined to the ecliptic, but Mercury never attains anything like the same distance from the plane of the ecliptic which is attained by the remote planet Uranus, whose path is of all others the least inclined to the plane of the ecliptic. In fact, none of the planets, except Venus and Mars, have so small a range from the ecliptic in actual distance as Mercury has.) The reason why the range of Mars from the ecliptic appeared so much greater than that of Saturn, in 1877, is similar to the reason why Mars, though much smaller than Saturn, largely outshone him. Mars looked larger because he was nearer, his loop looked larger because his real path was nearer. For the same reason that a hut close by seems to stand higher above the horizon than a palace at a distance, or a mountain yet further away, so the displacement of Mars from the ecliptic plane appeared greater than that of Saturn, though in reality much less.

Let us consider how the paths of these planets are really situated. I know of no better way of showing this than by drawing the paths of the two families of planets separately. It is in fact utterly impossible to give an accurate yet clear view of the solar system in a single picture; and the student may take it for granted that every drawing or plate in which this has ever been attempted is from one cause or another misleading.

In figs. [17] and [18] the shape and position of the planetary paths are correctly shown. Very little description is necessary, but it may be mentioned that on each orbit the point nearest to the sun is indicated by the initial letter of the planet, while the point farthest from the sun is indicated by the same letter accented. The places where each path crosses the plane of the earth's—which is supposed to be the plane of the paper—are marked ☊ and ☋, the former sign marking where the planet in travelling round in the direction shown by the arrows crosses the plane of the earth's path from below upwards, while the latter marks the place where the planet in travelling round crosses the plane of the earth's path from above downwards.

Fig. 17.—The paths of Mercury, Venus, the Earth, and Mars, around the Sun.

[Fig. 17] shows the paths of the inner family of planets of which our earth is a member. [Fig. 18] shows the outer family of planets, and inside of it the ring of small planets called asteroids. Inside that ring, again, we see the paths of the inner family of planets; but they appear on a very small scale indeed. In fact, the scales appended to the two figures show that a length which represents 50,000,000 miles in [fig. 17], represents 1,000,000,000 miles in [fig. 18]; or, in other words, the scale of [fig. 18] is only one-twentieth of the scale of fig. 17. On the scale of [fig. 17] the sun would be fairly represented by an ordinary pin-hole; on the scale of [fig. 18] the sun would be scarcely visible. The dots round the orbits show the planets' places at intervals of 10 days in [fig. 17], and of 1000 days in [fig. 18], starting always from the left side of orbit (on horizontal line through sun).

Fig. 18.—The paths of Jupiter, Saturn, Uranus, and Neptune, around the ring of small planets.

Now looking at [fig. 18] and noting how small is the distance of the path of Mars from the earth's path, compared with the distance of Saturn's path, we understand why Saturn, despite his far superior size, shines far less brightly in our skies than Mars does. In fact, in October, 1877, the Earth and Mars were on the parts of their tracks which lay nearest together, that is, the parts occupying the lower right-hand corner of [fig. 17]; and turning to [fig. 18], we perceive that the distance separating the two paths here is very small indeed compared with Saturn's distance.

So that, when we looked at Mars and Saturn as they shone in conjoined splendour in our skies, in 1877, we saw in the bright orb of Mars the planet whose track lies nearest to us in that direction, whereas in looking at Saturn the range of view passed athwart the track of Mars, through the ring of asteroids, and past the orbit of Jupiter, before entering the wide and barren region which separates the orbits of the two giant members of the solar system.