Astronomers can take cosmic temperatures with specialized equipment

Photo: Wikipedia

The Dominion Radio Astrophysical Observatory, south of Penticton.

The Dominion Radio Astrophysical Observatory near Penticton sometimes gives tours to groups from local schools.

The tours often include demonstrations to help show what radio astronomy is all about. One of the devices that is occasionally rolled out for these tours is "The Cannon".

The equipment consists of a piece of copper tube around eight centimetres in diameter and about a metre long. On the end is a complex aluminium structure looking rather like a horn or the mouth of a blunderbuss. It is mounted, along with some electronics, on an equipment cart, so it intentionally looks like the sort of cannon pirates used to have lined up along the sides of their ships.

The device is completely harmless. It is a piece of prototype equipment used with the 46-metre in diameter dish in Algonquin Park, Ontario. The dish catches the weak radio emissions from cosmic radio sources and concentrates them at one point, the focus of the antenna, where they are collected by devices such as the one used in The Cannon.

Everything in the universe having a temperature higher than absolute zero (-273 C) emits radio waves. This is the idea behind the cannon demonstration. Volunteer students stand in front of this somewhat scary-looking device, so staff leading the tour can detect the radio emissions they are producing. It shows an important application of radio telescopes—we can use them to measure the temperatures of objects out in space, even if they are too cold to produce light or infrared radiation.

For example, we can measure the temperature on the moon without going there by just pointing a radio telescope at it. By making measurements at different wavelengths, we can measure temperatures at different depths below the soil level, and learn about the heat flows during the long lunar days and nights. That tells us about the composition and nature of lunar soils.

Using radio telescopes as cosmic thermometers has given us a few surprises. Maybe one of the biggest was when attempts were made in the 1950s and 1960s to measure the temperature of Venus.

Until then, because Venus is about the size of the Earth, permanently covered by cloud and closer to the sun, many scientists thought the planet's surface might be covered with a hot, steamy jungle, with lots of alien life forms waiting to be discovered.

Some, for no solid reason, hypothesized Venus could be like our planet as it was hundreds of millions of years ago. Then radio telescopes were turned on the planet. They revealed temperatures hot enough to melt lead and tin. However, the steamy jungle idea was so attractive, at first it was argued that those radio measurements were of the hot upper atmosphere, not the surface.

Finally, as the data accumulated, we had to accept Earth's sister planet is truly a hostile, hot, dry furnace of a world.

Radio telescopes have been used to measure the temperatures of other planets, and the temperatures of the dust and gas clouds between the stars. However, one of the most important discoveries was made by two engineers.

In 1964, Arno Penzias and Robert Wilson made accurate temperature measurements of radio emissions from the sky. They used an antenna shaped like a huge horn. However, they ran into a problem. No matter how carefully they did the measurements, the whole sky was three degrees Kelvin warmer than it should be.

Coincidentally, at the same time, Robert Dicke and other scientists finished a calculation that predicted if the universe started with a Big Bang, the echoes of the event should still be detectable and it would be a radio emission with a temperature of three degrees Kelvin.

Dicke and his co-workers had their answer. The universe started with the Big Bang. That three degree Kelvin emission is now known as the Cosmic Microwave Background.

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• The planetary line-up continues. Saturn lies low in the southwest sunset glow. Moving to the left (eastward) find brilliant Venus, then Jupiter, almost as bright and finally Mars, conspicuously red.

• The moon will reach last quarter on Feb. 20.

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