Feature

Pioneering Radio Astronomy

For a brief time in the late 1940s, New Zealand played a very active role in the emerging field of radio astronomy.

Dr Wayne Orchiston

Fifty years ago, in 1945, observations in New Zealand contributed to the development of the new science of radio astronomy, with the discovery of radio waves emitted from the Sun. British-born scientist Elizabeth Alexander, who was responsible for analysing these observations and recognising their significance, ranks as one of the world's first female radio astronomers.

The exciting field of "radio astronomy" was born in 1931 when a young US radio engineer named Karl Jansky discovered radio waves from the sky. This gave astronomers a new way of looking at the universe, but idea that radio astronomers could contribute significantly to our understanding of the universe only emerged during the 1950s, largely as a result of important advances during and immediately after World War Two. Very few people realise that New Zealand played an important role at this time as one of four countries responsible for the independent discovery of radio waves from the Sun.

Between 1939 and 1945 scientists in Germany, England, the United States and New Zealand independently detected radio waves coming from the Sun, but because of security issues these discoveries were largely kept secret until after the war.

Norfolk Island Effect

The New Zealand discovery occurred between 27 March and 1 April 1945 when a large increase in "radio noise" was noted by operators of a 200 MHz Royal New Zealand Air Force radar unit located on Norfolk Island. This increase only occurred within half an hour of the rising or setting of the Sun.

Dr Elizabeth Alexander, a government scientist with the Radio Development Board, was assigned to investigate this phenomenon, which was dubbed the "Norfolk Island Effect".

Alexander arranged for monitoring of the Sun to take place within one hour of sunrise and sunset at five different locations where there were New Zealand radar units -- Norfolk Island, itself, North Cape, Whangaroa, Maunganui Bluff and Piha.

This challenging research project brought immediate results for, during April, all five radar stations recorded solar radio emission. These observations demonstrated to Alexander that "... the Norfolk Island effect was significant and was connected with radiation from the sun ...".

In the light of these findings, Alexander proposed an even more elaborate solar monitoring programme for the second half of 1945, this time involving a combination of Air Force, Army and Navy radar units. As part of this observational programme, New Zealand's very first dedicated radio telescope was set up on the cliffs just south of Piha Beach. Despite being a rather primitive device, it could follow the Sun all day long and was able to detect "noise signals" -- radio waves -- coming from the Sun.

Although observations were carried out between July and December 1945, intense radio emission from the Sun was recorded at these stations for a short interval only, centred on October 5. At this time "...violent surges of noise were observed at irregular intervals."

In her summary of the observations carried out in March, April and October 1945, Alexander concluded that there was a direct correlation between the presence of sunspots on the Sun's disk and the occurrence of radio bursts from the Sun.

At the end of the war, Alexander was reunited with her husband (who had been interned in Singapore) and resigned from the DSIR in order to return to England. As a result she never got to write up a detailed scholarly account of the important radio astronomy discoveries she made while in New Zealand.

Peacetime Projects

But solar radio astronomy did not die with her departure, for the government approved a new peacetime atmospheric research project using one of the WWII radar units set up at Ashburton in South Canterbury. The Director of the Carter Observatory, Ivan Thomson, was aware of Alexander's exciting findings and prevailed upon the officer in charge to track the Sun each day after sunrise.

This monitoring took place between March and December 1947, and a large number of solar bursts of short duration were detected. On many occasions these occurred when sunspots and other visual signs of solar activity were in evidence. However, Thomson never published the results of this collaborative project.

While the so-called "Canterbury Project" solar work was in progress a student named Alan Maxwell embarked on a solar radio astronomy project for his MSc thesis at what is now the University of Auckland. His Masters thesis was one of the first completed anywhere in the world specifically on solar radio astronomy. In mid-1947 he erected twin Yagi antennas on the roof of the Biology Department and tracked the Sun during 1947 and 1948. Of particular interest was a period of solar activity between August 5-8 1948, when there were numerous small-scale bursts of radio noise. Unfortunately Maxwell left for England shortly after this in order to enroll for a doctoral degree, so he never did publish his results. (He's now Emeritus Professor Maxwell of Harvard University).

Australian Connection

The results of the solar radio observations carried out in New Zealand in 1945 were shared with the allies through appropriate military channels and inspired the Division of Radiophysics of the CSIRO in Australia to take up this line of research. Alexander's pioneering findings were soon replicated and greatly expanded on, and the Sydney group went on to achieve international pre-eminence in solar radio astronomy.

Meanwhile, two Sydney scientists, British-born John Bolton and Gordon Stanley, a New Zealander, were intrigued by British reports of the discovery of a "radio star". They quickly found the strange new object, Cygnus A, and soon discovered a number of others. The only way they could determine the true nature of these enigmatic objects was to record very accurately their positions in the sky. To do this, they needed to determine their precise rising and setting times.

This was best done from a high cliff-top location looking out over the sea -- something which Sydney could not offer. At the end of May 1948, Bolton and Stanley shipped an ex-Australian Army radar trailer containing four Yagi antennas, a radio receiver and weather-recording equipment to Auckland.

For two months, the radio astronomers worked at a site near Leigh, observing the rising of two different radio stars. Then they moved their little mobile radio telescope out west to Piha, to record the setting times of the objects. The weather was so cooperative at Piha it took them just three weeks to make useful observations of four different radio stars.

Armed with this priceless New Zealand data, Bolton and Stanley went on to identify the sources of three of the four radio stars and to show for the first time that radio astronomy could provide useful information about the universe.

Not much remains at the old radar site at Piha beyond a few concrete foundations; the equipment and buildings were all removed in the 1960s.

Despite the auspicious start, New Zealand was to play no further major part in radio astronomical research until the 1970s, when a group from the University of Otago under Professor Paul Edwards became active.

We can but hope that these pioneering efforts will inspire some future young astronomers to pursue this exciting field at the forefront of modern astronomy.

Dr Wayne Orchiston is the Executive Director of the Carter Observatory in Wellington.