Joseph ¨M Rumolo, age 11, of Staten Island, New York, for his question:
Is there a way to make a small radio telescope?
A gossipy person, they say, can make a mountain from a molehill. In the gabby world of gossip, it also may be possible to kid a mountain down to the size of a molehill. But radio telescopes are giants of the factual world. And not one of them can be kidded down to vest pocket daze.
The purpose of a radio telescope is to bring in radio signals from outer space. A miniature model might bring in a tuneful program from your local radio station or more likely a spatter of static from the nearest thunderstorm. It would, of course, be an ordinary radio receiving set. But its limited scope would disqualify it as a radio telescope. The real cosmos probing instrument was discovered by accident and the first model was 100 feet long. The man who made it called it a merry round and only later did he discover that it really was a radio telescope.
The man was Karl Jansky, just out of engineering college. The Bell Telephone people employed him to track down static that was upsetting radio signals from ships and ocean cables. Jansky built a huge skeleton of brass pipes, 100 feet long, supported on a wooden frame. Metal surfaces reflect radio waves, somewhat as mirrors reflect light and assorted spurts of static were gathered from all directions. The brassy skeleton was turned by a motor and rotated on four wheels salvaged from an old Model T. Ford automobile.
The static interference was focused into a receiving set and Jansky listened with ear phones. He tracked down various sources of local interference, but one strange source refused to be identified. After a year of patient listening, Jansky concluded that these steady radio hisses were coming from a point far out in the universe. They were indeed coming from beyond the constellation Sagittarius, near the heart of the Milky Way:
Jansky made his astounding contraption way back in the early 1930s. Astronomers paid little attention to it, but another radio engineer built his own version of the radio telescope in his back yard. He was Grote Reber and his model used a shallow disc of shiny metal 32 feet wide. This might not be your idea of a small radio telescope. But so far as Andy could discover, this 10 yard model seems to be the smallest one on record. It gathered weak, short wave radio signals from space and focused them on an antenna at the center of the disc. There the pulses of cosmic radio energy were amplified by a receiving set.
Radio telescopes came into style after the invention of radar. They were needed to analyze the radio output of the sun and astronomers began to see their wider cosmic possibilities. Newer models got better as they grew bigger. Reflecting discs were made 100 and then 150 feet wide. The largest disc type radio telescope at present is 250 feet in diameter. Its huge round ear is rotated across the sky by massive machinery and supported firmly on massive scaffolding.
Most radio telescopes translate their cosmic signals into written grasps. But the receiving set can be hooked up to a loud speaker and the cosmic radio programs can be heard by the human ear. There are assorted whistles and whispers, shouts and shrieks. A trained expert can identify several sources of radio signals from their sounds. Jupiter puts out a low roar of mumbles and grumbles. The sun sends radio signals like soulful sighs and the.Milky Way puts out a steady, faraway hiss.