Tuesday, 17 January 2012

A Short History of Radio Astronomy

NSF was lucky enough to hear a talk by Dr Haida Laing (School of Science and Physics, Nottingham Trent University) on the History of Radio Astronomy.

The talk was part of the “Stargazing LIVE” event at Wollaton Hall, Nottingham on 17th Jan 2012

As is often the case, the talk opened up a series of vistas on areas of knowledge that you didn’t know you didn’t know and forms the basis of this blog post (any errors are probably mine, not Dr Liangs). . . .

The first radio astronomers weren’t professional astronomers.
One of the founding fathers of radio astronomy was Karl Guthe Jansky, who was working at Bell labs on radio communication antennas at Bell Laboratories in the US. In 1932 he built an antenna that could be rotated and measured the radio reception in various directions for several months. After categorising most of the signals as thunderstorms he wondered what could be causing the other static he was he was receiving. Noting that the static correlated with the sidereal day as opposed to the solar day, he realised that it was coming from outside the solar system and eventually pinpointed the source as being the centre of the Milky Way.

In recognition of his pioneering work, the strength of radio sources is measured in Janskys

Replica of Jansky's antenna

Sidereal Day? Wassat?
Dr Liang helpfully explained the difference between a solar(i.e.24hr) day and a sidereal day. This is one of those things that is best explained by a picture rather than a bunch of words (but if you need a bit more info, go here):

Explanation of a Sidereal Day

Grote Reber, a man doesn’t mess about.
In 1933, Grote Reber, an amateur radio operator in the Chicago area, was inspired by Janskys work and, in 1937 he built a 9metre radio telescope in his back garden, as you do.

He first repeated Janskys work and then went on to make a radiofrequency map of the sky, which he completed in 1943.

Sadly, Grote would have to wait a while before he could receive Sky. . .

Still No Professionals
There were further advances by Southwork (Bell Labs) and James Hey (a British physicist) in the early 1940s before the professional astronomers finally pulled their socks up and entered the game. . .

At Last, the pros arrive
1944 saw the Dutch astronomer Jan Oort (as in Oort cloud) and Van de Hulst (one of Oort’s students) predicted the presence of a 21cm (1420Mhz) radio frequency Hydrogen spectral line - something that could give information about the speed that gas clouds are moving at and allow the structure of the galaxy to be determined. But actually making a telescope that could detect this proved to be a difficult challenge that was not solved until, in 1951, Ewen and Purcell finally detected the line in radio emissions from the milky way using a horn telescope at Harvard.

Since then, telescopes have, or course, got bigger and bigger. . .

Parkes antenna

Arecibo antenna


Why Radio Astronomy
The two key benefits of radio astronomy are that the atmosphere is relatively transparent to radio waves and that radio waves are much better at travelling through interstellar dust clouds of dust than visible light is. In addition, some structures are visible in the radio spectrum that are not visible in the visible spectrum.

For example, in the image below, the left side is a visual image of galaxy 0313-192 overlaid with a radio frequency image in red, which shows the galaxys’ radio emitting jets. The image on the right is a close-up of inner portion of the jet. (NASA)

Whilst the image below shows the radio lobes of the Centaurus A Galaxy overlaid on a visible spectrum image (Hubble)

Finally, Dr Liang also mentioned some of the arrays coming on stream in the future :

Square Kilometre Array


Image Sources : Jansky, Time, Grote, Parkes, Areciebo, SKA, VLA, ALMA, Galaxy

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