New views of the cosmos

Light, radio waves in space

In the 1930s, Karl Jansky, an engineer and scientist with Bell Telephone Laboratories, was given the task of assessing the interference environment in which planned radio communications networks would have to operate.

In the process he discovered radio emissions coming from the Milky Way. This discovery marked the birth of the science of radio astronomy.

The (optical) astronomical community largely ignored what Jansky found, but radio amateur Grote Reber did not, and built the world’s first radio telescope, a 10-metre diameter dish that could be scanned up and down. He produced the first radio map of the sky, which was essentially an image of the Milky Way—what we would see if we could look at the sky with radio eyes.

The image showed a sky dominated by a brilliant Milky Way. There were no signs of any stars. Seeing the sky through "radio eyes" shows us a universe very different from what we see with our eyes. Unless you have spent a few nights out in the country, under really dark, clear skies, you have probably never seen the Milky Way. In cities, we are lucky to see the brightest stars and planets.

Light and radio waves are both types of electromagnetic waves. In order of increasing wavelength these are gamma rays, x-rays, ultraviolet, visible light, infrared and radio. All these waves come in fixed-size “packets,” called “quanta,” which just means packets.

A single packet is referred to as a “quantum.” The amount of energy needed to make a quantum depends on the wavelength. It needs an enormous amount of energy to make a quantum of gamma rays, and a tiny amount to make one of radio waves.

We see a starry sky with our eyes because stars have enough energy to generate quanta of light. Black holes, neutron stars or supernovae produce immense amounts of energy, enough to make gamma rays and x-rays. However, cold, almost empty space has a very small energy density, only enough to make quanta of radio waves. We only see the Milky Way with our eyes because millions of stars light up the clouds of cosmic gas and dust.

Our radio telescopes make it possible to image the clouds of gas and dust, and regions where high-energy electrons interact with the cosmic magnetic fields. Combining the radio and optical observations gives us a better picture of what is going on out there. Then of course we can fold in the gamma ray and x-ray observations of the high-energy objects, such as black holes, neutron stars and supernovae. Ultraviolet observations tell us about extra hot stars and clouds of hot gas. Infrared observations are used to study dust and gas clouds, particularly those forming new stars and planets. The universe is such a complex place, with conditions in some places more extreme than anything we are familiar with on Earth. This makes it very difficult or impossible to guess from, say, a radio image what the ultra-violet image would look like. It is only by integrating together the "pictures" obtained at many observing wavelengths that we can get a realistic impression of what is going on.

However, there is a complication our atmosphere blocks of all the electromagnetic waves coming in from space other than light and radio waves. This is good for us because gamma rays, x-rays and ultraviolet radiation are highly dangerous to living things. We can observe those waves by putting our telescopes above the atmosphere, in space.

Over the last decade or two the number and quality of the instruments and analysis tools we have for studying the universe have improved immensely. This will answer a lot of questions and no doubt raise at least as many new ones.


• Venus, Mercury and Mars lie low in the dawn glow.

• Jupiter and Saturn shine in the south after sunset.

• The Moon will reach its first quarter on Jan. 17.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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