Jodrell and Cambridge: A shared radio astronomical heritage

18th April is World Heritage Day, and as the UK’s newest World Heritage Site, this is a good opportunity for us to reflect on our new status. This year’s theme is Shared Heritage.

Jodrell Bank became a World Heritage Site in July 2019, in part because the site is the only one in the world that retains traces of the development of radio astronomy from its earliest days to the present. This extraordinary story that is written across the landscape of Jodrell Bank, from the remains of the 1946 searchlight aerial; an instrument for the radar detection of meteors, through the majestic Lovell telescope, to the shiny new headquarters of the Square Kilometre Array.

But why is the story of radio astronomy so important? Why does it have the ‘Universal Value’ that UNESCO look for in a site of international importance? The development of radio astronomy marked a revolution in our understanding of the universe; it has been the basis of the 20th and 21st century’s great leaps forward in astronomy and cosmology, such as the cosmic microwave background, the search for extra-terrestrial intelligence and the recent imaging of a black hole. And crucially it also paved the way for astronomy in other wavelengths, such as infrared and x-ray. It is in multiwavelength astronomy that we now get the most colourful and detailed picture of the universe.

These developments have had a profound impact on humanity; on how we understand our own place and our planet’s place in the universe; our ‘pale blue dot’.

But although our site tells this story, the story doesn’t belong exclusively to Jodrell. Radio astronomy emerged as a new science after the second world war. Although two notable individuals, Karl Jansky and Grote Reber, had detected galactic radiowaves earlier than this, it was war time radar research that inspired physicists, such as Lovell, to see whether radar could be used to study the sky. This happened simultaneously and most significantly at four sites: Jodrell Bank, the Cavendish Laboratories in Cambridge, the British Army Operational Research Group and the Council for Scientific and Industrial Research Organisation in Sydney, Australia. Open a correspondence file from the Jodrell archive of this period and you will find many letters between Lovell and the leaders of these research groups; sharing data, asking questions, reporting new developments, requesting corroboration, outlining hypotheses.

There was a particularly strong relationship between Jodrell and Cambridge. Lovell and Cambridge’s Martin Ryle were similar in many respects. Both had worked for the Telecommunications Research Establishment during the war, developing radar systems, before returning to their respective universities where they applied their wartime expertise to their research.

The 1949 letters below are part of a series between the two men from the exciting early days of radio astronomy. They had turned their radio receivers to the skies and found that the universe was indeed transmitting in radio frequencies; the possibilities of seeing what had previously been invisible was starting to unfold. The areas of interest were in the constellations of Cassiopeia and Cygnus, and Lovell speculates about the cause of fluctuations in the signal and asks his peer ‘Is there any fallacy in this reasoning?’.  Ryle responds three weeks later with his own speculation and encloses their own tracings of Cygnus and Cassiopeia plus their ‘activity charts’ so Lovell can make the comparison for himself.

The ongoing dialogue between scientists was critical in the rapid development of radio astronomy, that went from bouncing radar signals off meteors in 1946 to the first mapping of an extragalactic radio source – the Andromeda Galaxy – just four years later.

Radio astronomers in these early years had no real contact with optical astronomers; the phenomena they were discovering didn’t correspond to anything before seen in optical astronomy, and their processes were entirely different. Each research site had different equipment and approach; Cambridge for instance had a number of small aerials and concentrated on the technique of combining them to obtain a sharper view. Jodrell focused on the use of larger, single dishes, allowing them to detect much fainter and more distant radio sources. Neither could get a complete picture but by working together, along with the team in Sydney and, in the next few years an increasing number of sites around the world, they mapped the entire radio sky and created a revolutionary new window into the universe.