Richard Lies, age 10, of Garden Grove, California, for his question:
At what speed is the earth moving?
Our dizzy old world spins and whirls in several different directions,each at a different speed. Every year it swings in a complete orbit around the sun. It makes this 600 million mile trip at an average speed of 18 1/2 miles per second. Meantime, the sun and its orderly family are moving in an immense journey around the Galaxy. It takes 200 million earth years to complete one of the cosmic trips. The sun, the orbiting earth and other members of the Solar System travel this stupendous journey together. In neat formation, they swoop through the starry heavens at an average speed of 170 miles per second.
Our dizzy globe also spins around on its axis like a top. The axis is a line through the center from pole to pole and the earth completes one turn with every calendar day. However, because it turns on an axis, the exact poles do not spin around at all. As the globe bulges toward the equator, the surface rotates faster. The wide equator must rotate fast est. Every spot on this bulging line spins around at about 1,000 miles per hour. Cindy and Sandy Wulff, age 11, of Panama Heights, Ohio, for their question:
\What use are ultraviolet rays?
In small quantities, ultraviolet rays are healing and healthful and able to perform dozens of useful industrial duties. In large quantities, they are killers. Of course, water also can be either healthful or fatal. Enough is enough and, as with everything, too much is too much.
Seething, searing ultraviolet rays come from the sun. They arrive in a dynamic package along with ordinary light, radio and several other forms of electromagnetic energy. Most of the sunlight gets through the atmosphere, but most of the ultraviolet is filtered out by the air and its dusty particles. Above the atmosphere, an unprotected spaceman would be sizzled by the full force of solar ultraviolet rays. Down on earth, the ultraviolet in summer sunshine tans our skins and adorns our cheeks and noses with artistic freckles. But an overdose causes blistering sunburns.
The energy of ultraviolet has many uses but it must be used sparingly. We can separate small quantities from ordinary sunlight. And we can produce small quantities with chemicals and electric current. But when `we deal with even such small doses of ultraviolet, the watchword is caution. The rays are invisible.
Ordinary glass blocks off ultraviolet rays, but quartz crystal and glass made of quartz let them through. A lamp using quartz or quartz glass directs an ultraviolet beam of.' invisible ultraviolet, or black light. Its rays are strong enough to kill germs and ultraviolet beams are used to purify foods and drugs. It may be used to enrich milk with extra vitamin D. It may be used to sterilize water and the air in an operating room.
Ultraviolet from an ordinary sunlamp is used to speed the healing of wounds or perhaps to treat certain skin diseases and sickness caused by poor diet. But remember, even weak ultraviolet is dangerously destructive to sensitive eye tissues. No sensible person goes near a sunlamp without the protection of proper goggles.
Ultraviolet rays make certain substances glow with fluorescent colors. Some glow under the beam, others give off their telltale colors after periods of exposure to ultraviolet. Prospectors and rock hounds use little portable quartz lamps to identify minerals and to test ores.
The most common use of ultraviolet is in fluorescent light bulbs. It is created by chemicals and electric current. The glass tube contains mercury vapor and when current passes through this sensitive gas, it gives off invisible rays of ultraviolet. The inside of the glass tube is coated with chemicals that convert ultraviolet into visible light. Different chemicals convert the ultraviolet to different colors. Fluorescent lamps are useful because they use a small amount of electric current to shed a large amount of very bright light.
The wave lengths of ultraviolet energy are shorter than the shortest wave lengths of ordinary light. They come after the blue bands of the rainbow colored spectrum. The shortest visible rays of violet have wave lengths of about 16 millionths of an inch. Ultraviolet rays have wave lengths ranging from this size down to .16 millionths of an inch. At the other end of the visible spectrum is a band of invisible infrared. These rays are longer than the longest red rays of visible light.