Three times a day a measurement is transmitted from the Dominion Radio Astrophysical Observatory of the National Research Council to a list of recipients around the world.
Some use it directly; others archive it and make it available on their websites, along with other data.
The measurements are made with two small radio telescopes, called “flow monitors”. The data consists of measurements of the intensity of the solar radio emission at a wavelength of 10.7 centimeters. It is used by those who take part in activities where, in one way or another, they are affected by the sun. These include communications services, space mission managers and various infrastructure services.
The data is known as “10.7 cm solar radius flux” or simply “F10.7”. This service has its roots in World War II.
In 1942, anti-aircraft radars sweeping the sky over Britain, looking for assailants, suddenly became unusable. Huge signals flooded any possible echo. The display screens, which should have shown radar echoes, were full of random dots and spots.
These things are now called “snow.” The radars were blocked. The first fear was that Britain’s air defenses were being hit by some secret weapon.
Then one of the engineers turned off the transmitter of one of the radars and moved the antenna while looking at the screen. Those traffic jams came from the sun. It was a relief to know that there were no secret weapons, but because every time the sun did what it did, the air defenses deteriorated; information about solar “attacks” was kept secret until after the war.
During this same war, warships at sea used their radars to sweep the horizon for any possible enemy ship. Operators soon realized that when the radar antenna was pointed at the rising or setting sun, the echoes of that direction were flooded by the same kind of “snow.”
Because this phenomenon could be used by potential attackers, it also remained as quiet as possible.
World War II was a high-tech war. He saw an explosion in the use of advanced radar systems and communication devices, along with efforts to manufacture equipment to jam or counterfeit enemy radars and communication devices.
When the war ended there were heaps of this advanced electronics that were no longer needed.
The Milky Way’s natural radio broadcasts had been discovered in the 1930s, launching the embryonic science of radio astronomy. The availability of military antennas and unwanted reception systems provided a gold mine for making radio telescopes.
During the war, the National Research Council was a hub for the development of radar systems. After the hostilities ended, NRC scientists used fragments of these radar systems to make Canada’s first radio telescope. They aimed the instrument at various objects in the sky, but the only thing they could detect was the sun, so they decided to accurately measure these solar radio emissions and how they varied.
Early in the war, Britain shared its military secrets with the United States and Canada. These include the resonant cavity magnetron. This device could generate high transmitter power at centimeter wavelengths.
This was especially necessary for airborne radar systems; short wavelengths mean that smaller antennas can be used. It is difficult to accommodate large antennas on aircraft. The magnetrons operated at a wavelength of about 10.7 cm, so did the radars.
So did the NRC radio telescope. It turned out that measurements of solar radio emissions at this wavelength were a good indicator of the full range of solar activity,
That is why this service has continued to this day.
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Venus is low in the glow of dawn. To his right are Mars and Jupiter, together, and then Saturn. The moon will reach the first quarter on Tuesday and will be full on June 14.
Ken Tapping is an astronomer at the Dominion Radio Astrophysical Observatory of the National Research Council near Penticton.