Looking into Space with Radio Eyes
July 1954 Popular Science

July 1954 Popular Science [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Popular Science, published 1872-2021. All copyrights hereby acknowledged.

In 1933, Karl Jansky, at Bell Telephone Laboratories, reported electromagnetic radiation coming from the center of our Milky Way galaxy in the direction of Sagittarius. It was the first time radio signals were knowingly detected in space. I say knowingly because there were likely others who noticed the energy but did not realize their source. This, by the way, was not the cosmic microwave background radiation (CMBR) that Penzias and Wilson discovered, also at Bell Labs, a decade later in 1964. Reported in this 1954 issue of Popular Science magazine are advances made in radio astronomy since the early efforts to detect and map the radio sky as a supplement to the visible light map. In most cases at the time, "radio stars" were coincident with known visible light stars; however, new stars were discovered which had no visible signature. Since that time, with the advent of larger telescopes and vastly more sensitive light detectors, many of those radio-only stars have been determined to also have a visible light component. Quite interestingly, the author mentions, "Many radio stars outshine the sun in radio 'brightness.' A bright one in the constellation of Cygnus, the Swan, was the first discovered, by Australian observers." Could this have been Cygnus X-1, the first x-ray star determined to be a black hole, which was discovered in 1971?

Looking into Space with Radio Eyes

By P. A. O'Brien

Cavendish Laboratory, Cambridge

The world's largest radio telescope has gone into service at Cambridge, England. Four parabolic sections, each 300 feet long and 40 feet wide, focus incoming radio waves upon antennas to locate radio "stars" - heavenly bodies that radiate at radio frequencies.

Radio astronomy is a new science. The first radio star was discovered in 1948. Now more than 200 are known; and Cambridge's new radio telescope should increase this number to about 1,000. Some actually are nebulae, but our sun, a faint radio star, is one example of a true star among them. They account for mysterious hissing radio noises from nowhere on earth, which observers since 1931 had tried to trace with the directional aerials called radio telescopes.

A new window into space opens to radio astronomy. Now astronomers can observe the skies by radio waves, as well as by visible, ultraviolet and infrared light. All are electromagnetic waves, differing only in wave length. And radio waves that pass unhindered through the earth's atmosphere, ranging in length from 1/4 of an inch to 60 feet, offer a vast spectrum thousands of times as extensive as the visible one.

Because of radio waves' similarity to light, a radio astronomer can do far more than listen to static from the stars. He views heavenly objects and makes actual pictures of them by radio "light."

Seeing the Sun by Radio

How does the sun "look" by radio? Its disk swells in apparent size. According to the wave length used, a bright ring may encircle it - or its shape may startlingly change from round to oval.

Sunspots, dark to the eye, become far brighter than the rest of the disk, vividly flickering and flaring.

The sun looks bigger by radio waves because they come mostly from its atmosphere - which we see only in a total eclipse, when scattered light from the sun's surface forms the faint pearly white corona. Appearance changes with wave lengths because different ones come from different heights. Radio astronomy unexpectedly finds the sun's upper atmosphere at million-degree temperature, compared to its 6,000-degree surface.

Many radio stars outshine the sun in radio "brightness." A bright one in the constellation of Cygnus, the Swan, was the first discovered, by Australian observers. Soon after, the brightest of all was found in the constellation of Cassiopeia by Martin Ryle and his Cavendish Laboratory group at Cambridge.

Precise measurements at Cambridge of the two "stars'" positions were sent to Mt. Palomar, and photographs with the 200-inch telescope showed two strange objects faintly visible there.

New-Found Wonders of the Sky

The Cassiopeia radio star proves to be a nebulous, 100,000,000-mile-diameter Milky Way cloud in a chaotic state of turmoil, with filaments of gas moving at up to 1,000-mile-a-second velocity.

The Cygnus radio star looks like two distant galaxies in collision! Such swarms of stars might pass through each other unscathed, in millions of years; vast distances separating stars would make direct hits unlikely. But gas and dust clouds between stars could not escape collision. Most of the gas would be left behind at the scene, and heated to extreme temperature by the impact.

While radio astronomy led to finding these wonders, and more like them, some radio stars are familiar objects. The third-brightest radio star has been identified with the famous Crab Nebula in Taurus, the remains of a supernova or exploding star. Notably the brightest radio stars have one thing in common - diffuse gaseous matter in violent motion.

Day or night, the "radio sky" is dark and seeing is good for observers at radio telescopes. Neither clouds nor city lights bother them. But a handicap is their instruments' inferiority to optical telescopes in resolving power, the ability to define details clearly, which depends upon a telescope's diameter measured in wave lengths. It would take a radio telescope as large as the Pacific Ocean to match the resolving power of the 200-inch Palomar telescope!

What is next-best? One answer is to build a single radio telescope as large as physically possible. Due for completion at Manchester, England, in 1955 is a bowl-type radio telescope of record 250-foot diameter, steerable toward any part of the sky. Under direction of Prof. A. C. B. Lovell, work on the million-dollar instrument is well advanced.

Another answer is the interferometer-type radio telescope, with two or more aerials, up to one-third of a mile apart, joined by cables to one receiver. The effect is as if the aerials were small portions of one gigantic one. The new Cambridge radio telescope is of this type - a "double interferometer" - unprecedented in resolving power, as well as in size. To sweep the heavens, it depends upon the earth's rotation. Meanwhile a wavy line upon a chart records in-coming radio waves' strength. Its units tilt to cover the sky in strips.

Observations with these two new instruments should bring about the next great advance in radio astronomy.

Here's the New Way the sun looks, by radio "light." Bigger than by visible light (far left), it enlarges with increasing wave length, and its round shape changes into an oval one (far right on facing page). Another striking feature is bright ring observed at one-inch wave length. PSM artist's paintings are based on brightness charts obtained with radio telescope and shown on smaller scale above them. Colors symbolize different wave lengths. This is an apt analogy, since changing the wave length alters celestial bodies' appearance much as a change of color filters does in visible-light observation. Note that visible sky is bright in daytime, "radio sky" always dark - a boon to radio astronomers.

Posted January 24, 2024