We can examine this meteor light by using the spectroscope and spectrograph. Through these specially designed instruments we can make the meteor light reveal the chemical elements present in the incandescent masses. Each such element sends out light rays as characteristic of its nature as fingerprints are of the individual who made them. Photographs taken of these characteristic light rays are called spectrograms, and what might be termed the “fingerprints of light” recorded on these spectrograms are known as spectra—which is the plural of the word spectrum. If the source of light is a meteor, the photograph shows a meteor spectrum.
From a study of a considerable number of good quality meteor spectra, scientists have found that the principal elements in the masses responsible for meteors are iron, calcium, manganese, magnesium, chromium, silicon, nickel, aluminum, and sodium.
As we have already noted, the resistance encountered by meteor-forming particles as they dash through our atmosphere is so great that they become incandescent and vaporize. These small bodies must therefore be in very rapid motion.
Before we attempt to find out the nature of the paths in space followed by meteorites, we must take into account the fact that these bodies are observed from a station—the earth—which is itself in rapid motion. You may have noticed that on a still day, when rain drops fall vertically downward, the streaks they leave on the windows of a swiftly moving car are not vertical but almost horizontal. Obviously, it would be wrong to say the rain drops are falling from left to right or from right to left when they are actually falling almost straight down, and it is only the forward motion of the car that makes them leave horizontal streaks.
Diagram showing meteorite moving along a “closed” (elliptic) orbit, e, which intersects the earth’s orbit, E. Held by the gravitational attraction of the sun, the meteorite is a permanent member of the Solar System.
Similarly, neither the apparent speed nor the apparent direction of motion of a meteorite with respect to the moving earth is significant. The important factor is the meteorite’s velocity with respect to the sun at the time the meteorite is picked up by the earth.
Diagram showing meteorite moving across the earth’s orbit, E, along an “open” (hyperbolic) orbit, h. The meteorite is traveling at such high velocity that it will pass right through the Solar System and back out into space unless it should chance to collide with the earth or another planet. The sun, however, in any case is able to change materially the direction of motion of the transient visitor to our Solar System.
This factor enables us to determine in which of two possible kinds of path the meteorite was moving before it was “fielded,” as we might say in baseball, by the earth. This factor tells us whether the meteorite was moving about the sun in a relatively short, closed, oval-shaped path or, instead, was following an indefinitely long, open path which began in the depths of space and would have returned there if the collision with the earth had not prevented.