Fig. 132.—Meteorite of Iron Etched with Acid.
Meteors and Meteorites.—If you will look at almost any part of the sky on a clear night when there is no Moon you will no doubt see a bright flash like a rocket. But if you will scan the sky during the dark nights of August and November you will be very apt to see dozens of these shooting stars or meteors.
Now, meteors, fireballs, shooting stars and meteorites are all one and the same thing to start with and they have their beginnings when some comet goes to pieces.
After a comet breaks up, the pieces of stone and iron which form it still travel round in the same orbit. Some of these pieces may get within range of the Earth’s force of gravitation when they are drawn to it, and on striking the air they are intensely heated by the friction, and if they are small they burn up before reaching the ground.
The smaller meteors burn up almost instantly and the shining tails they leave last only a few seconds. Fireballs, which are simply large meteors, leave burning trails which can sometimes be seen for several minutes. Shooting stars are merely meteors which are not very bright, while meteorites are meteors which have fallen to the Earth before they have had time to burn up.
Many meteorites have been found, but ninety-five out of every hundred are of the stony kind, the others being of the iron kind. The way to tell a meteorite from a common stone is by examining its surface. A true meteorite is covered with a black, shiny, burnt crust, caused by the intense heat to which it was subjected as it fell through the air. The test for an iron meteorite is to grind and polish a part of its surface and then cover it with a dilute solution of nitric acid, when markings like those shown in [Fig. 132] will be etched upon it.
Fig. 133.—The Milky Way.
The Milky Way.—You have, no doubt, often seen on a clear, dark night, a wide, ragged band of light stretching from the northern sky across the celestial equator and beyond. This band of light is the famous Milky Way.
If, as you were looking at the Milky Way, the Earth could be moved from under you and you were left standing in space alone so that you could see in every direction, you would find that the band formed a complete ring round the sky.