Winston Freeman, age 13, of Dayton, Ohio, for his question:
WHAT IS A SPECTROSCOPE?
A spectroscope is an instrument used to examine spectra. The simplest spectroscope is a triangular prism.
Substances heated to a high temperature give off light. This light may be separated into a pattern of colors by passing it through a prism. The pattern is the spectrum for that substance. "Spectra" is the plural of the word spectrum.
No two materials have the same spectrum. For this reason, an expert can identify any substance by its spectrum. Any instrument he uses to examine spectra is called a spectroscope.
A person who looks through a prism, preferably with the aid of a small telescope, sees a band of colored images of the light source. These tend to overlap and blend into each other. Less overlapping occurs if the source is narrow and its images are sharply focused.
For the best possible separation of the colored images, the light source is placed behind a narrow slit. The slit is attached to one end of a tube, and a lens is attached to the other end, so that a beam of parallel light rays emerges from the lens.
This part of the spectroscope is the "collimator." The light from the collimator passes through the prism and then through a telescope to the eye of the observer.
Spectra of heavenly bodies are often obtained with a compound spectroscope. This consists of a series of prisms arranged in the arc of a circle. The spectroscope is attached to the eyepiece end of a large telescope that forms an image of the heavenly body on the slit of the spectroscope.
By using spectra obtained in this way, an astronomer can determine the chemical composition of the sun, the stars and of the atmosphere of planets. The astronomer can also determine the speed at which the body is moving toward or away from him by measuring small shifts in the spectrum lines.
A spectroscope may use a diffraction grating instead of a prism to separate light into different colors.
Modern graftings are made by ruling straight grooves with a diamond on a glass surface or on a metal mirror.
The graftings resemble the grooves on a phonograph record, but are much closer together. About 15,000 grooves per inch are common.
The spectrum formed by a glass grafting is seen by looking through it.
A spectrograph is an instrument for photographing a spectrum, which is the pattern of colors formed by light passing through a prism. A spectrograph is actually a spectroscope with a camera instead of a telescope.
Spectroheliography is an apparatus that allows one color of the sun's spectrum to be photographed. An image of the sun, obtained through a telescope, is allowed to pass through a slit of the spectrograph. The spectrum thus obtained is transmitted through a second slit that allows only light of a selected wave length to pass to a film behind it.