Before radio signals, observatories were where time came from: Greenwich dropped its public time ball from 1833 so ships on the Thames could set their chronometers. The Belville family made a business of it — John Belville, and later his daughter Ruth, carried a pocket chronometer nicknamed Arnold from Greenwich to London subscribers each week, selling the time itself. Ruth Belville was still making her rounds in 1940, in her eighties, as the telephone speaking clock finally ended the trade.
Time-seller no longer exists as a living trade. Here is what erased it, and which profession took on the work.
1600 – 1800
The telescope changes the question
Galileo's telescope made the sky a place with landscapes rather than a pattern of lights; Kepler's laws turned planetary tables into physics; Newton's Principia of 1687 explained both at once. National observatories at Paris (1667) and Greenwich (1675) put astronomers on the state payroll to fix longitude and time, and in 1781 a Hanoverian musician in England, William Herschel, doubled the solar system's known size by finding Uranus from his back garden.
What else was happening then
1838
Bessel measures a star's distance
At Königsberg, Friedrich Bessel measured the annual parallax of the star 61 Cygni: about a third of an arcsecond, placing it roughly ten light-years away. The measurement — which rivals Thomas Henderson and Wilhelm Struve nearly beat him to — ended a two-thousand-year argument over whether the distances to stars could ever be known.
1912
Leavitt's law creates the cosmic ruler
From photographic plates of the Small Magellanic Cloud, Harvard computer Henrietta Swan Leavitt showed that a Cepheid variable star's pulsation period reveals its true brightness, turning Cepheids into distance markers. Every cosmic distance measured since, including Hubble's, stands on a relation published in a three-page circular issued under the observatory director's name.
1929
The universe is expanding
Using Mount Wilson's 100-inch telescope, redshifts largely measured by Vesto Slipher and Milton Humason, and Leavitt's law for distances, Edwin Hubble showed that galaxies recede at speeds proportional to their distance. Georges Lemaître had derived the same law theoretically in 1927 in a French-language Belgian journal; in 2018 the IAU voted to rename it the Hubble–Lemaître law.
1967
Bell Burnell finds the pulsars
On 28 November 1967, Cambridge PhD student Jocelyn Bell Burnell confirmed that a quarter-inch of recurring "scruff" on her radio survey's chart paper was a source pulsing every 1.337 seconds — the first pulsar, a spinning neutron star. The 1974 Nobel Prize for the discovery went to her supervisor Antony Hewish, an omission still argued about.
Where that work lives now
The scientist who measures the universe, from Babylonian clay tablets to space telescopes, still deciding which flicker in the data is a discovery.
🔭 Astronomer →