Professor Thomas Henderson (1798-1844) was Scotland’s first Astronomer Royal. A native of Dundee, he travelled as far as South Africa to work at the Cape Observatory, before returning home to his prestigious appointment at the Royal Observatory in Edinburgh.
The Royal Observatory sits on the summit of the Calton Hill directly across from the Nelson Monument. Surrounded by a high stone wall and built in the shape of a cross with a dome in the centre, the gable ends on each of the four sections face north, south, east and west. Designed to resemble an ancient Greek temple, the roofs on each section are supported by six pillars cut from Craigleith stone.
Opened in 1818, the Royal Observatory was designed by William Henry Playfair and funded by the Astronomical Institution of Edinburgh. A clock was placed in the window of a small stone building standing outside the observatory. Landing at the Port of Leith, mariners climbed the hill to the transit house to set their chronometers with the time on the clock. Known as the ‘politician’s clock’ as it was fitted with a face at the front as well as the rear, the transit house clock was also used by the townspeople to set their watches.
In the early nineteenth century, the world’s naval and merchant fleets, especially the UK’s, were expanding rapidly. In addition to collecting information for star charts, the astronomers supplied data for the Admiralty’s nautical almanacs used by navigators to determine their ship’s position at sea. Using the observatory’s nine-foot long transit telescope, Alexander Wallace, the assistant observer at the time, obtained the data by observing the position of the stars.
Thomas Henderson was appointed Astronomer Royal for Scotland in 1834. Born in Dundee in 1798, his mother, Isabell Henderson, was widowed early and left to raise five children. Thomas, the youngest, was educated at Dundee Grammar School before enrolling at Dundee Academy at the age of eleven. Run by the Town Council, the academy, which stood in the Nethergate, specialised in teaching mathematics and the various branches of science connected with the subject. The rector Thomas Duncan, a brilliant mathematician, described Thomas as being ‘everything that was good’.
In addition to supplying the time and lecturing on astronomy, mathematics and natural philosophy at Edinburgh University, and assisted by Wallace, Professor Henderson began recording the hundreds of observations he had made during the time he had spent as astronomer at the Cape Observatory. He also found time to track the orbits of several comets. In their lifetimes, Henderson and Wallace compiled five volumes of the ‘Edinburgh Astronomical Observations’ while a sixth was in the process of being completed. The publications led to the work being carried out at the observatory being recognised by scientific institutions all over the world.
While working at the Cape Observatory, Thomas had decided to measure the distance from the Earth to the star Alpha Centauri using an astronomical method known as parallax. Although he had established the existence of a parallax to a fraction of a second, he decided to delay publishing the results. A meticulous researcher, he continued to check his findings to ensure that his calculations were accurate before announcing the result – and was beaten to it by Friedrich Wilhelm Bessel. This German mathematician had been working on the same project and published his research in October 1838; the first astronomer to officially measure the distance between the Earth and a star.
A few years later, when Friedrich Wilhelm Bessel accompanied by Carl Gustav Jacob Jacobi arrived in Scotland on a visit, Thomas Henderson, ever the gentleman, not only took the mathematicians on a tour of the Highlands but also presented Bessel with a daguerreotype of the Royal Observatory.
In recognition of the outstanding work he was carrying out, Thomas was elected a member of the Royal Society of London in 1840. That same year an official residence was provided for Scotland’s Astronomer Royal and his wife at 1 Hillside Crescent at the foot of the Calton Hill. Thomas had married Janet Mary Adie the eldest daughter of Alexander Adie the optician and instrument maker two years after returning to Scotland from the Cape of Good Hope. When Janet Mary died in 1842 a few weeks after giving birth to a daughter, the infant was handed over to her relatives to look after.
Unable to come to terms with the death of his wife, and the long hours spent in the observatory combined with the steep daily climb from Hillside Crescent, Thomas Henderson died of hypertrophy of the heart in November 1844. Scotland’s first Astronomer Royal is buried in Greyfriars Kirkyard. His successor, Professor Charles Piazzi Smyth, set up a memorial stone to Henderson which can be seen on the wall of west section of the observatory facing Arthur’s Seat. In addition, the names of Thomas Henderson and Friedrich William Bessel, first astronomers to measure the distance from the Earth to a star are inscribed on the ornamental stonework of the main observatory building on Blackford Hill.
Refurbishment work starts on the Royal Observatory on Calton Hill in June.
Further information can be found on the observatory can be found on the One o’ Clock Gun Association website: www.piazzi.co.uk
Images of the Royal Observatory East Tower and Thomas Henderson are courtesy of Wikimedia Commons. Professor Henderson’s portrait is an original drawing by Angus McBride, based on a sketch made by Professor Piazzi Smyth.