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Ken Tapping, January 28, 2009
In the sky this week...
> Venus dominates the southwestern sky after sunset.>
> Saturn rises around 9 p.m.> The Moon will reach First Quarter on February 2.
Radio waves are like light waves, only longer. We can record their strength or make images with them, just the way we can with light waves. If that were the whole story, why bother? If using radio telescopes to map the sky is just a more technically challenging way of seeing what we see with ordinary telescopes, particularly excellent ones like Gemini and the Canada France Hawaii Telescope, why not stick to optical astronomy. Obviously that is not the case. Radio telescopes show us things about the universe invisible to telescopes using light. Moreover those things are really important. It is fair to say that radio telescopes have shown us a face of the universe that we never knew existed.
On a clear, dark night you might see two or three thousand stars, and maybe a planet or two. If the sky is dark enough, you might see the Milky Way, crossing the sky like a great arch. You'll see the Moon and some meteors. Sometimes you'll see a comet. A radio telescope will show you something so different that for decades it was hard to relate all we saw with radio telescopes with what we were seeing with optical telescopes.
To radio telescopes the Milky Way is the brightest thing in the sky. What's more, when we look at the Milky Way with our eyes, we see a stream made up of millions or billions of faint stars. The bright radio emissions from the Milky Way don't come from the stars at all. They come from the space between them: from gas, dust, high-energy particles and magnetic fields. Almost all of this stuff is invisible to the naked eye. Some radio emission comes from the clouds of cold hydrogen gas, the main ingredient for making stars. Most of the chemicals in the dark clouds of cold dust have radio signatures, so using radio telescopes we can identify them and study the chemical reactions going on there. Cosmic chemistry is a subject that would not exist without radio telescopes.
In places we see bubbles blown in the gas clouds. This is where old stars have exploded, blowing holes in the clouds. The magnetic fields and shock waves around the explosions produce radio emissions. On the wall at our observatory we have a picture of something that looks like a jellyfish. In the sky it would look bigger than the Full Moon, except that this object is giving off radio waves, not light waves. Our Synthesis Radio Telescope discovered it. Another star exploded close to a gap between two clouds, making something looking like a baseball being caught by someone using a huge catcher's mitt. All of this stuff is totally invisible to our eyes, but our radio telescopes show it.
Radio telescopes show us a very special view of the universe; one of chemical reactions in dark, cold clouds making materials that could have been important in the development of life. We see the raw material for making stars, shock waves, jets of material ejected from galaxies, and strange, high-energy processes taking place in the centres of galaxies. It was a radio telescope that serendipitously showed us the radiation forming the fading breath of the birth of the universe. Without radio telescopes our knowledge of the universe would be in a much poorer shape.
Ken Tapping is an astronomer at the National Research Council Herzberg Institute of Astrophysics (NRC-HIA), and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9 Tel (250) 493-2277, Fax (250) 493-7767,