Bringing Stars Closer

            You have probably used a magnifying glass to make things look bigger. Perhaps as long ago as the thirteenth century someone though of arranging two such magnifying glasses, or lenses, to make an instrument for viewing distant objects. This instrument is called a light telescope. A light telescope focuses light from distant objects so they seem nearer and larger.
            In 1609 Galileo, an Italian astronomer, built a light telescope. His was the first telescope used for detailed study of the sky. Galileo's first telescope magnified objects to appear three times bigger than normal. His later telescopes magnified objects to appear thirty times bigger. With his telescopes Galileo discovered many stars that were too faint to be seen with the eye alone. He saw craters and mountains on the moon. He even discovered sunspots and four of Jupiter's moons.
            A telescope does two things. (1) A telescope gathers the light from an object. It then concentrates that light in a small area. This makes the object seem brighter. (2) A telescope forms a magnified image of the object. This makes the object appear to be closer and larger.
            Some light telescopes contain only lenses. A large lens gathers light from an object and focuses it, forming an image. Another lens – more often two lenses – magnifies the image made by the large lens. This kind of light telescope is called a refracting telescope.
            Other light telescopes contain mirrors and lenses. A large, curved mirror gathers light from an object and focuses it on a small, flat mirror. The flat mirror reflects the light to a small lens or lenses that magnify the image. This kind of telescope is called a reflecting telescope.
            Very often a camera is attached to a telescope. The film in the camera can be exposed to the light from a star or other object for a long time. In this way, the light striking the film builds up for several hours. As a result, the photograph of the star is much brighter than what could be seen with the telescope alone.

Tuning in Space

            In 1931 scientists discovered that radio waves are sent out by some objects in space. Telescopes of a different kind were built to measure the strength and direction of these radio waves coming from space. Radio telescopes, as they are called, receive radio waves from the sun, the moon, some planets, and many other distant objects. This doesn't mean that someone on the sun or the moon is sending radio messages. Objects in space send out many forms of energy that travel as waves. One form of energy travels as radio waves. These radio waves are just like the waves used to carry radio broadcasts on the earth. Another form of energy is light waves. Still other forms of energy are infrared waves and ultraviolet waves.
            With the aid of radio telescopes, astronomers have discovered very distant objects in space. Radio telescopes have also been used to measure the temperature of objects in space.
            Interference from the many radio sources on the earth can cause problems for people using radio telescopes. To overcome these problems, radio telescopes are built in valleys. The mountains around the valleys screen out radio waves transmitted on the earth. But radio waves from distant objects in space are then easily detected.

Viewing Stars from Space

            Smog, clouds, and light from nearby cities can make the work of an astronomer very difficult. One way to solve these problems is to study the stars from space. The view is clearer as you move away from the earth's atmosphere.
            The first observations made from space were carried out by a rocket launched in 1946. Photographs of the sun were returned to the earth from the rocket. Today many satellites, or space vehicles circling the earth, keep constant watch on the earth and space. Photographs of their findings are sent back to the earth.
            Information about some of the planets has been gathered through space probes. These are spacecraft guided through space by instruments on the earth. Space probes have passed close to Jupiter and Mercury. Probes have landed on Venus and Mars. Television cameras on board have given scientists much information about these planets.
            One outstanding observatory in space so far has been Skylab. Skylab was our first space station. Scientists were sent there to experience life in space for a few months. Our knowledge of the sun and other space objects has been greatly increased because of the observations from Skylab.

People Who Keep Track of the Universe

            Imagine turning on the sun, lighting up the moon, or putting the stars in motion. Sound like an impossible job? Not if you work in a planetarium!
            A planetarium is usually a building with a huge dome painted white inside. The dome serves as a rounded movie screen. A machine under the dome projects on the screen something very much like the sky in miniature. Inside the planetarium, visitors can sit back and watch the planets revolve around the sun. What happens during a whole year in the sky can pass before their eyes in moments.
            Many people who work in a planetarium are astronomers. These astronomers plan demonstrations and exhibits to help people understand many things about the universe. They may show the path of a comet expected to appear that year. Or they may treat the audience to an imaginary journey into space.
            Astronomers working at planetariums may also teach college classes in astronomy. Or they may make audiovisual presentations for grade-school and high-school students studying about the universe.
            Some astronomers are advisers for the space program. Other astronomers study the sky with telescopes at observatories. They may also do research at a university.