Portsmouth cosmologist celebrated for his part in solving centuries-old London mystery

A University of Portsmouth researcher has helped solve a 350-year old mystery in the heart of the UK capital.

Last week (31 October) London’s Lord Mayor Professor Michael Mainelli closed a series of scientific experiments held as part of his mayoral priorities at an event in the city. The series brought together academic researchers and industry experts to solve complex challenges.

One of these was to help answer a centuries-old question about the London Monument, which was built by Robert Hooke and Christopher Wren in the 1670s to commemorate the city’s reconstruction after the Great Fire of 1666.

The structure, a 61-metre Doric column, was also designed to act as a zenith telescope to prove Earth’s motion around the Sun. But Hooke’s attempts to recreate the measurements that would reveal this relationship did not work, and until now the reason why was unknown.

Professor Enrique Gaztanaga from the University of Portsmouth’s Institute of Cosmology and Gravitation (ICG), was part of a team tasked with solving this mystery.

The ‘Monument Measurement’ experiment proved that the pillar’s shape makes it unsuitable for its lesser-known second purpose to act as a giant telescope.

This is because, although the tower was built to be as rigid as possible, its tall structure would always make it prone to vibrations, and those vibrations are big enough to stop the positions of the stars being measured accurately.  

Up to now, the limiting factor has been thought to be road traffic – with this theory dating back to the 1670s. But the team’s work has revealed that both traffic and wind gusts contribute to the tower not doubling up as a telescope, as per Robert Hooke’s vision. 

Professor Gaztanaga said: “This story revolves around three critical numbers: +23, -21, and ±25 (arcseconds northern deviations of Gamma Draconis star), marking a journey through time. The first is a measurement by Robert Hooke in 1669, the second a prediction by James Bradley in 1727, and the third, our recent vibration error estimate prepared for the Lord Mayor in 2024. Was Hooke’s + value a sign error or a vibration artefact? After 350 years, we’ve resolved why The Monument couldn’t serve as a telescope. Yet, it endures as a symbol of the scientific revolution, an era devoted to uncovering the universal laws of physics and humanity’s place within the cosmos.”

Earlier this year, Professor Gaztanaga was awarded the Freedom of the City of London, for his outstanding achievements in the field of space, data and academia.

The Working Group for Measurement the Monument, lead by Professor Philips Thomas (4th from left) and participating members from the City of London University, Imetrum, WCSIM and City Optotech Ltd, with Professor Enrique Gaztanaga from the University of Portsmouth as science advisor 

The Freedom of the City dates back to 1275 and originally meant that a Freeman was not bound to a feudal lord and could own their land and property. In Mediaeval times, Freedom was necessary for anyone wanting to trade in the City and provided immunity from tolls at markets and freedom from impressment into the armed forces. 

Although most of the practical privileges of having Freedom have now disappeared, the award is still seen as a huge honour and Professor Gaztanaga does now have the right to drive sheep over London Bridge, toll free.

High-profile recipients of the award include theoretical physicist Professor Stephen Hawking, Archbishop Desmond Tutu, former prime minister Winston Churchill and Professor Dame Sarah Gilbert, who initiated and led the development of the Oxford-AstraZeneca COVID vaccine. 

Professor Gaztanaga is also a Professor at the Institute of Space Sciences (CSIC/IEEC) in Barcelona and publishes a science blog called Dark Cosmos.