The Sun Kings: The Unexpected Tragedy of Richard Carrington and the Tale of How Modern Astronomy Began
- Stuart Clark
During the nineteenth century, astronomy was transformed from a mathematically oriented science preoccupied with mapping the positions and movements of celestial bodies to a physical science aiming to understand their nature and constitution. In The Sun Kings, science writer Stuart Clark offers a captivating account of this tortuous and passionately fought century-long transformation.
The tale centres around the solar astronomer Richard Carrington and his observations of the gigantic solar flare of 1 September 1859. Carrington, who today is little known outside the field of solar physics, happened to witness this event while drawing sunspots at his private observatory. Most solar flares can be seen only with modern spectroscopic equipment and so this white-light flare was very rare. The nearby Kew geomagnetic observatory recorded a weak magnetic disturbance lasting only 10 minutes, but exactly coincident with Carrington's flare. There was a violent geomagnetic storm 18 hours later and a worldwide display of the most magnificent aurorae, together with electric surges that disrupted telegraph communications.
Carrington's suggestion of a connection between the flare on the Sun and the geomagnetic disturbances and aurorae was largely dismissed and ridiculed. Even 40 years later, Lord Kelvin, then president of the Royal Society, presented a 'proof' against a solar connection in an address published in Nature. Kelvin based his proof on Maxwell's electromagnetic theory to show mathematically how it would be energetically impossible for the Sun to cause the observed disturbances in the Earth's magnetic field. Around that time Kelvin also pronounced that “there is nothing new to be discovered in physics now. All that remains is more and more precise measurements.”
The case for the solar connection was finally won in 1905, in a series of debates at the Royal Astronomical Society, thanks to the statistical analysis of Walter Maunder and the physical arguments of Joseph Larmor, the new Lucasian professor of mathematics at Cambridge. Larmor invoked the recently discovered electron to make the case that beams of charged particles from the Sun disturbed Earth's magnetic field. He suggested that “investigations of this rich tapestry of particle interactions beckoned, and would distinguish the twentieth century from the nineteenth”.
One of the first to advocate turning astronomy into a physical science was the eminent astronomer William Herschel in the early 1800s. His call fell on deaf ears because it was related to another idea of his that was ridiculed, namely that the number of sunspots was statistically related to the price of wheat in England. Herschel was seeking a connection between sunspots and climate, which we now know exists. He used the price of wheat as a proxy for temperature, because there were no data on global temperature. Herschel found that when there were more sunspots, wheat was cheaper, implying warmer weather and bigger crops. Today's satellite observations show that the radiative output from the Sun is indeed higher when the sunspot number peaks.
The imprint of Carrington's 1859 flare could be seen in an ice core retrieved from Greenland in 1992. The proton beams from solar super-flares produce nitrates in the Earth's atmosphere, which get deposited in the ice. Of all the flares of the past 500 years, the 1859 flare was one of the most powerful.
The most revolutionary tool for the physical exploration of stars was spectroscopy. Dark lines in the solar spectrum were noticed by William Wollaston in 1801 and rediscovered by Joseph von Fraunhofer in 1814, who later mapped these lines in much greater detail with his invention, the diffraction grating. Robert Bunsen and Gustav Kirchhoff showed that these absorption lines were the fingerprints of chemical elements — despite the famous French philosopher's Auguste Comte 1835 pronouncement that we would never know how to study the chemical composition of the stars.
Stuart Clark weaves all these events and ideas together in a fascinating tapestry. The account is accurate while being non-technical, and is suited for anyone with a general interest in the history of science. Clark's engaging writing style conveys the passion, intrigues and captivating life stories of the main players. It is a gripping tale of the birth of modern astronomy.
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Stenflo, J. Science with flare. Nature 448, 27–28 (2007). https://doi.org/10.1038/448027b