1.The Evening Sky. -As the light of the sun fades in the evening, we see the stars coming out one by one until at last the sky is studded with them. We notice, too, that the brighter the star is, the sooner itPART OF THE MILKY WAY.
The plate for this photograph was exposed ten hours and a quarter.
appears. In the morning, just the reverse of this takes place, the stars begin gradually to fade, and the brightest stars are the last to disap- pear.
We know how brilliant the light of a match or candle appears in a dark room, and how a light of this kind seems to fade out when it is brought into the presence of a strong electric light. It would seem quite probable that the vast light of the sun might have the same effectDOME OF THE 60-INCH REFLECTING TELESCOPE AT MT. WILSON SOLAR OBSERVATORY.
Pictures of the heavens are taken through a telescope.
upon the light of the stars. This supposition is also supported by the fact that when the sun is covered in an eclipse the stars begin to appear as in the evening. Astronomers are all agreed that if it were not for the greater brilliancy of the sun we should see the heavens full of stars all the time.
In the northern hemisphere the stars, except those at the north, which seem to go around in a circle, appear to rise in theeast and to set in the west, just as the sun does. If we observe the stars which rise to the east, southeast, and northeast of us, we shall find that these are above the horizon for different lengths of time.
The ancients noticed these facts, and explained them by saying that the earth was at the center of a hollow sphere, upon the inner surface of which were the stars, and that this sphere was continually revolving about the earth and also slightly changing its position in respect to the earth. We of the present day know that it is the earth that is turning around on an imaginary axis, and also gradually changing its position in relation to the stars. We also know that this axis, if extended far enough, would almost strike a star in the center of the northern heavens, which we call the North Star. The points on the surface of the earth through which the axis passes are called the poles.
2.The Earth as one of the Planets. -If we carefully observe thebright points which appear in the sky at night, we shall see that almost all of them shine with a twinkling light. There are, however, three of the brightest which give a steady light like that of the moon. When the positions of these three bodies are carefully observed for some time, it will be seen that they are continually changing their places among thestars, whereas the positions of the stars do not appear to change in relation to each other.
One of these three brightest points has a reddish brown color and has been named Mars, from the Roman god of war. The other two bear the names Venus and Jupiter, one namedfrom the goddess of beauty and the other from the king of the Roman gods. Astronomers call the earth and these three bodies, together with four others, planets, and tell us that they revolve around the sun as a center. They have no light of their own as do the true stars, butthe light which comes to us from them is a
reflection of the light of the sun.
MARS.
Most like the earth of all the planets. It is supposed to have a polar ice cap.
The unaided eye is able at some times to see five of these planets. Astronomers tell us that their change of place in relation to the stars is due to their motion about the sun. If we could stand upon one of these visible planets, our earth would appear to us like one of them. But the surface of some of these planets, like Jupiter or Saturn, is not solid likeTHREE VIEWS OF SATURN.
The planet with the beautiful rings.
that of the earth. Our sun, if seen from the distance of one of the stars, would appear like a star.
The list of the planets in the order of distance from the sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The sun, with the bodies revolving about it, is called the solar system. There is reason to believe that ours is only one of many similar solar systems that exist throughout space.
HALLEY"S COMET.
One of the most famous visitors from outer space. The small white dots are stars seen through the tail.
The planets are by far the nearest of all the starlike bodies, although the di stance from the sun to the farthest of the planets is some 2700 million miles greater than the distance from the earth to the sun. The distance of the nearest of the stars however, is probably about25,000,000,000,000 miles. This distance is so great that it takes light, which travels at the inconceivable rate of 186,000 miles in a second of time, over four and a half years to come to us from this star. From Arcturus, another of the stars, it takes light about 180 years to reach us, and from others very much longer. Sometimes from this outer space comets visit our solar system. Thus we see that our little earth is only a speck in the universe.
In the space between the planets Mars and Jupiter, there has been found a group of small bodies which are called planetoids or asteroids. The brighest of these is Vesta, not more than 250 miles in diameter.
A f a m o u s t h e o r y , c a l l e d the Nebular Hypothesis, was suggested many years ago to account for the formation of our solar system. This theory supposes that the materials of which the members of the solar system are composed once formed a cloud or nebula of finely divided matter filling anenormous space, and that this matter, by reason of the mutualDIAGRAM OF THE SOLAR SYSTEM.
Showing roughly the positions of the various planets and their moons.
attraction of the particles, gathered together into what is now our sun with its planets and their satellites. Man is unable to comprehend howmatter originated or how matter can either be created or destroyed. But we do know many of the properties of matter.
3.Properties of the Matter Composing the Universe.
