ASTRONOMY.

ASTRONOMY treats of the heavenly bodies, and tells all about the sun, the moon, the planets, the stars, etc. As the earth is one of these planets, it tells all about it also.

Planets. Some of the stars shine with a clear steady light, and as they change their position in the heavens they are called planets, meaning wanderers.

Fixed Stars.-Then there are other stars that remain immovable. although their light is twinkling; these are called fixed stars.

Milky Way.-Spanning the heavens diagonally is a whitish vapory belt, like a luminous cloud. It is really a stream of suns, divided into two branches, and consists of countless multitude of stars whose light blends. Herschel states that 258,000 stars passed across the field of his telescope in forty-one minutes.

History. This is the most ancient of the sciences. The study of the stars is as old as man himself.

The Chinese boast of their discoveries, and their emperor calls himself the Son of the Sun. They have the first record of an eclipse in 2128 B C, and two of their chief astronomers, Ho and Hi, were put to death for failing to announce a solar eclipse, 2169 B. C.

The Chaldeans were among the earliest observers. Their priests were astronomers, and their temples were observatories. When Babylon was taken by Alexander, 331 B. C., he found that observations had been made reaching back nineteen centuries, nearly 4000 years ago.

The Greeks and Egyptians were also close observers.

Among more modern astronomers, COPERNICUS was the first to teach that the earth revolved around the sun, and that it revolved on its own axis once in twenty-four hours.

Kepler's Laws.-TYCHO BRAHE was a famous Danish astronomer, who did a great deal of work, but lacked the ability to apply it, but his pupil, Kepler, discovered three great laws that bear his name. The first law is, that "Planets revolve in ellipses, with the sun at one focus." The second law is, that “A line connecting the centre of the earth with he centre of the sun passes over equal spaces in equal times." The third law is, that The squares of the times of revolution of the planets about the sun are proportional to the cubes of their mean distances from the sun.”

Galileo was contemporary with Kepler. He discovered the laws of the pendulum and of falling bodies. Learning that a Dutch watchmaker had invented an instrument for making distant objects appear near, he soon had a telescope completed, with which he examined the moon, and saw her mountains and watched the dense shadows upon her plains. January 8th, 1610, he turned his telescope toward Jupiter, and near it saw three bright stars, and later on a fourth star . . Poor Galileo had the mortification of having to fight the prejudices of his time.

On

In 1666 Newton, then a young man 24 years of age, was spending the summer in the country, on account of the plague. One day sitting in the orchard, he saw an apple fall from a tree, and reflecting on this, he was 'ed to discover the famous law of gravitation, which is as follows: "Every

particle of matter in the universe attracts every other particle of matter with a force directly proportional to its quantity of matter, and decreasing as the square of the distance increases."

Space. The blue arch of the sky as it appears to us is termed the Celestial Sphere.

Only one-half of the heavens is visible at one time. The point directly over us is called the zenith, while the point directly beneath on the other side is the nadir. The vanishing point directly in front of us, where the sky seems to disappear, is the horizon.

The apparent path of the sun through the heavens is called the Ecliptic. This is the real path that the earth traverses in its course around the sun A Belt of the Celestial Sphere 8° on each side of the ecliptic is called the Zodiac. Certain constellations in the heavens correspond to the months, which is the time the earth occupies in traversing that portion of the heavenly sphere.

THE SOLAR SYSTEM.

is mainly comprised within the limits of the Zodiac. It consists of 1. The sun-the centre.

2. The major planets—Vulcan (undetermined), Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

3. The minor planets, at present 237 in number.

4. The satellites or moons, twenty in number, which revolve around the different planets.

5. Meteors and shooting-stars.

6. Thirteen comets, which have now been found, by a second return, to move, like the planets, in elliptic paths.

The Sun, the centre of this system, is at an average distance of 93,000,000 miles from the earth. Since the earth's orbit is elliptical, the sun is nearer the earth in January by 3,000,000 miles than it is in June. The nearest point to the sun is called the perihelion. The further point, which corresponds to the summer solstice, is called the aphelion.

To give some idea of the earth's distance from the sun, it would take an express train travelling at the rate of 30 miles an hour, day and night, 352 years to reach its destination. Or if a sound was made large enough to reach from the sun to the earth it would take that sound 14 years to

come to us.

The light of the sun is equal to that of 5,563 wax candles held at a distance of one foot from the eye.

Regarding the heat of the sun Sir John Herschel calculates that if a solid cylinder of ice, 45 miles in diameter, and 200,000 miles long, were plunged, end first, into the sun, it would melt in one second of time.

The diameter of the sun is 866,000 miles. The sun appears larger in summer than it does in winter. Through a telescope, or a smoked glass, the sun appears to be full of spots. These were noticed as early as the year 807. Sometimes, but rarely, the sun's disk is clear. During a period of ten years, observations were made on nearly 2000 days, and on about 400 of these there were no spots on the sun. These spots change from day to day, and take about 14 days for one spot to cross the disk of the sun from its eastern to its western side. Sir John Herschel first advanced the idea that the years of abundant sunspots would be also years of plentiful harvests. These spots are supposed to be depressions in the luminous surface of the sun. A telescope of moder

ate power will show the sun to have a mottled appearance like that of an orange peel.

One theory supposes that the sun is composed of a solid, dark globe, surrounded by three atmospheres. The first, nearest the black body of the sun, is a dense cloudy covering. The second, called the photosphere, consists of an incandescent gas, and is the seat of light and heat. The third, or outer one, is transparent, like our own atmosphere.

The theory now held is that the sun is a vast fiery body, surrounded by an atmosphere of substances volatilized by the intense heat. The different portions of the sun are thought to be arranged like this: (1) The nucleus, most likely gaseous. (2) The photosphere, a covering several thousand miles thick, constituting the visible part of the sun. (3) The chromosphere, composed of luminous

gas, mostly hydrogen, and the seat of enormous protuberances, tongue, of fire, which dart forth at the rate of 150 miles a second, and to a distan e of 100,000 miles. (4) The corona, an outer covering of faint pearly light, consisting of streamers reaching out often several thousand miles.

THE PLANETS.

The planets all move in the same direction around the sun from right to left, or from east to west. They are opaque, and shine by the light of the sun, and turn upon their axes the same as the earth.

The question sometimes arises-Are the planets inhabited? This of course no one can prove, but judging from the different conditions, similar to those necessary for life, we have good reason to believe that some of them are inhabited. The planets are divided into two classes. (1) Those whose orbits are inside that of the earth, Mercury and Venus. (2) Those whose orbits are outside that of the earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The planets between the earth and the sun, Venus and Mercury, are evening stars part of the time, and at others morning stars. The different planets are also morning and evening stars at different periods. are evening stars as follows:

The

is nearest the sun, and is visible only when the sky is clear, just about sunset, near the western horizon. It revolves around the sun at a distance of about 36,000,000 miles. Mercury's year is about 88 days, and its daily rotation is about the same as our earth. It is about 3000 miles in diameter. It is one-fifth denser than the earth, and a pound on the earth would weigh only about 7 oz. on Mercury.

Mercury is so much nearer to the sun than the earth that it would appear to the inhabitants thereof, if there were any, ten times larger than it appears to us.

VENUS

comes next. She is about 67,000,000 miles from the sun, and takes about 225 days to turn on her orbit, or about 71⁄2 months. She is 7600 miles in diameter, and has no moon.

THE EARTH.

Our own earth is next in order. It revolves around the sun at a distance of 93,000,000 miles. Its diameter is 79251⁄2 miles. Its circumference is about 25,oco miles. It weighs 6,069,000,000,000,000,000,000

tons.

SOLSTICES.

On the 21st day of June and the 21st day of December we have what is called the summer and winter solstice, which are the longest and shortest days of the year. At two other times, the 21st of March and the 21st of September, the days and nights are alike. These are called the Vernal and the Autumnal equinoxes. At this time the earth is said to be crossing the line.

The earth revolves upon its own axis once in 24 hours, causing day and night. It takes about 365 days to make a complete rotation around the sun.

THE SEASONS.

The change of seasons is due to the fact that the earth's axis: that is, the line running from the North to the South Pole, is not at right-angles or perpendicular to the path or plane that the earth describes in revolving around the sun. It is exactly as if the earth were a top spinning on one end, inclining to either side, so that first one side and then the other is brought under the influence of the direct rays of the sun. Then again summer is longer than winter because the sun is not in the centre of the earth's orbit, but nearer one end than the other, as the earth's orbit is elliptical.

THE MOON.

The earth has one satellite, the moon. This is at a mean distance of 239,000 miles from the earth. The moon completes her motion around the earth in 27 days, but as the earth is constantly moving in its orbit