Part 19

The most interesting feature about Jupiter for the amateur astronomer consists in observing four of its moons, which are visible with a small telescope. They appear like mere dots of light, and their transit of or occultation with the planet (that is, their disappearance before or behind its disk) can be watched, and is a never failing source of pleasure. A large telescope alone reveals Jupiter's four other moons.

SATURN.

Saturn is farther removed from the earth than any of the planets in the solar system, visible to the naked eye. It is distinguished from the fixed stars by the steadiness of its light, which is dull and of a yellow hue, though to some it appears to be of a greenish tinge. It seems barely to move, so slow is its motion among the stars, for it takes two and one half years to pass through a single constellation of the Zodiac.

Saturn has eight moons. Titan, its largest one, can be seen with a 3" glass. Its celebrated rings are telescopic objects but a small glass reveals them.

URANUS.

The student will hardly mistake Uranus for a fixed star, as it is only under the most favorable circumstances that it can be seen with the naked eye.

At its nearest approach to the earth, it is as bright as a sixth-magnitude star. Uranus is accompanied by four moons, and takes seven years to pass through a constellation of the Zodiac.

NEPTUNE.

Neptune is the most distant of the planets in the solar system, and is never visible to the naked eye.

The earth comes properly under a discussion of the planets, but a description of it is hardly within the scope of this work.

Confusion in identifying the planets is really confined to Mars and Saturn, for Venus and Jupiter are much brighter than any of the fixed stars, and their position in the heavens identifies them, as we have seen before.

The following table of first-magnitude stars in the Zodiacal constellations confines the question of identifying the planets to a comparison of the unknown star with the following-named stars:

Castor and Pollux in Gemini. Spica " Virgo. Regulus " Leo. Aldebaran " Taurus. Antares " Scorpius.

The first four stars named above are white in color, so that either Mars or Saturn is readily distinguished from them.

As for Aldebaran and Antares, which are both red stars, not unlike Mars and Saturn in color and magnitude, the fact that the latter do not twinkle, and that they do not appear in the diagrams, should satisfy the observer of their identity. Reference to an almanac, or a few nights of observation, will in any case set at rest any doubt in the matter.

THE MILKY WAY.

The Milky Way, or Galaxy as it is sometimes called, is a great band of light that stretches across the heavens. Certain portions of it are worthy of being viewed with an opera-glass, which separates this seemingly confused and hazy stream into numberless points of light, emanating from myriads of suns.

This wonderful feature of the heavens is seen to best advantage during the months of July, August, September, and October. Beginning near the head of Cepheus, about thirty degrees from the North Pole, it passes through Cassiopeia, Perseus, Auriga, part of Orion, and the feet of Gemini, where it crosses the Ecliptic, and thence continues into the southern hemisphere, beyond our ken in these latitudes.

It reappears in two branches in the region of Ophiuchus, one running through the tail of Scorpius, the bow of Sagittarius, Aquila, Delphinus, and Cygnus; the other above and almost parallel to it, uniting with the first branch in Cygnus, and passing to Cepheus, the place of beginning.

The student should note especially the strange gap between , , and Cygni. This dark space has been called the "Coal Sack."

The Milky Way in the vicinity of Cassiopeia is particularly rich, and well repays a search with an opera-glass.

"The Galaxy covers more than one tenth of the visible heavens, contains nine-tenths of the visible stars, and seems a vast zone-shaped nebula, nearly a great circle of the sphere, the poles being at Coma and Cetus."

THE MOTIONS OF THE STARS.

It may be that the student desires to proceed in this conquest of the sky at a more rapid pace than the scheme of study permits. To assist such, it should be borne in mind that the circumpolar constellations, as Ursa Major, Ursa Minor, Draco, Cepheus, and Cassiopeia, are designated,--are visible in our latitude in the northern sky every night.

A reference to their diagrams, and a glance at any of the large plates showing the entire group in their respective positions, will suffice for the student to identify them.

The hours of darkness alone limit the speed with which a knowledge of the constellations can be acquired.

Let us suppose that the student begins his search for the constellations on the night of April 1st, at nine P.M. He has for his guide the large plate, and the spring group of eleven constellations set forth in the diagrams. The remaining three constellations of the circumpolar group are, as we have seen before, visible in the north.

If he faces the western sky, he will see Andromeda just setting, and Perseus, Taurus, Orion, Lepus, and Canis Major but a short distance above the horizon. If he is so fortunate as to be able to identify these, and the spring group, he may turn his attention wholly to the eastern sky, where new constellations await him.