Armagh Observatory: A 200-Year Legacy

By Caleb Todd

Armagh Observatory is an astronomical research institution located in the centre of Armagh City. Throughout its over 200 years in operation the observatory has been at the forefront of astronomy in the UK and Ireland, supporting a rich history and housing many influential physicists from all reaches of the world. It has endured through challenging times to keep astronomy alive in Armagh and has a much greater historical significance than most realise.

The Armagh Observatory was originally founded by Archbishop Richard Robinson in 1790 during the Age of Enlightenment, a pivotal time where the study of science was increasing steadily based on the foundations of Galileo and Newton’s methods in the previous two centuries [1].

During the Observatory’s foundational years, the astronomers main focus was in measuring star positions, this was done using meridian and transit circles – instruments which utilised simple refracting telescopes to record the time planets crossed the meridian in order to measure their coordinates. In 1794 the Observatory purchased their first major instrument, the revolutionary Troughton Equatorial Refractor, this was intended to improve observations in the frequent poor, cloudy conditions in Armagh [2] and is now believed to be the oldest telescope in the world still in its original dome, and one of very few of its kind left [3].

Ultimately the complicated design of the telescope proved to not be as accurate as the simpler methods for position measurements. However, in order to obtain these results, the astronomers required temperature and pressure conditions to be measured daily, this resulted in the Observatory unknowingly beginning the longest record of unbroken temperature and pressure measurements in the UK and Ireland and one of the longest in the world [4]. These measurements date back to 1794 and are still made daily by physicists at the Observatory today, where they still utilise some traditional tools, alongside newer digital instruments.

On January 6th 1893 a windstorm hit Ireland causing widespread damage. The severity of this storm led to the Observatory’s third Director, Thomas Romney Robinson, wondering how to quantify the conditions of the storm, in particular the wind speed. This inspired him to design the Robinson Cup Anemometer for measuring wind speed, this instrument was revolutionary and remains to this day as the main inspiration for most modern anemometers [4]. A version built in this style is present at the Observatory today and used to measure wind speed, a record of which the Observatory has taken since 1843.

As well as temperature, pressure and wind speed, the Observatory records many other climate conditions such as cloud coverage and rainfall. Sunlight has been measured since 1880 using a Campbell-Stokes Sunshine Recorder which was invented by Sir George Gabriel Stokes, Robinson’s son-in-law and an influential physicist and mathematician credited for popularising Stokes’ Theorem. The conditions measured provide a valuable resource for understanding the climate and climate change in Ireland, with records now complemented by journals provided by local farmers and gardeners [5].

Robinson himself compiled a large catalogue of stars and wrote many related reports. In 1862 he was awarded a Royal Medal for his work before he was succeeded by John Louis Emil Dreyer as Director in 1882.

Dreyer’s ‘New General Catalogue of Nebulae and Clusters of Stars’ (NGC) is probably the single most important contribution to science to have come from Armagh Observatory. This record was compiled over 100 years ago and it remains to this day the principal catalogue of nebulae and galaxies used by astronomers around the world [6]. The NGC contains 7,840 objects which Dreyer listed and classified from previous observations, including observations made using The Great Telescope at Birr Castle Demesne in County Offaly and by himself at Armagh. He went on to win the Gold Medal of the Royal Astronomical Society in 1916, and now has a crater on the moon named after him.

Following the major successes of the Observatory in the 18th and 19th centuries, the beginning of the 20th century led to a tragic decline in scientific research in Armagh. The passing of the Home Rule Bill and the threat of civil war in Ireland broke the economic power of the rich anglo-irish landowners who had previously funded much of the scientific research of the time [7]. This resulted in the observatory losing its estates in 1914 and Dreyer leaving the observatory in 1916, ultimately causing a period of inactivity between the wars.

After years of struggle, hope was not lost for the Observatory, in 1937 Eric Mervyn Lindsay was appointed Director; educated at the King’s Hospital School, Dublin and Queen’s University Belfast, Eric Lindsay was on familiar terms with many of the Irish leaders of his time, both from Northern Ireland and the Republic [8]. At this time, the vast majority of telescopes were positioned in the northern hemisphere, causing an imbalance in observational astronomy [9]. After the end of the second world war he proposed that the Armagh Observatory and Dunsink Observatory (belonging to Trinity College Dublin) should, combined with Harvard University, set up a large telescope in the southern hemisphere at the Harvard Southern Station in South Africa, in order to both explore this gap in observation and once again provide all Irish astronomers access to high quality equipment and data.

The Armagh-Dunsink-Harvard telescope (ADH) was almost exclusively used for photography of stars and galaxies, gathering valuable data for use in the observation and understanding of the southern Milky Way and the Magellanic Clouds. The signing of the ADH agreement in 1948 was a significant achievement not just for astronomy but for the foundation of new relationships within Ireland, Butler describes this as “a milestone in cross-border cooperation in Ireland” [10] with it being one of the first North-South agreements following the partition of Ireland.

Coming into the modern age the Armagh Observatory welcomed Ernst Julius Öpik in 1948, a prominent astronomer who is known for his study on stellar evolution, including being the first to estimate the density of white dwarf stars and discussion of processes to fuse Hydrogen to Helium in stars [11]. Most recognizable however were his postulations for the origins of comets in the solar system which he, alongside Jan Oort, believed originated beyond Pluto in what we now call the Öpik-Oort cloud.

The Observatory expanded its horizons for the public in 1968 by opening the Armagh Planetarium, the now longest running planetarium in the British Isles, celebrating its 50th anniversary in 2018. The observatory is still in operation to this day with its main research focus being solar physics and supermassive black holes. The Planetarium has undergone several refurbishments since its construction, allowing it to remain at the forefront of knowledge for the public and educate people of all ages on the cosmos in an entertaining and informative way.

Sources:

[1] “A Short History of Armagh Observatory”, C.J Butler, accessed Feb 01, 2025, History and Archives of Armagh Observatory

[2] “J A Hamilton and the Early Instruments,” Armagh Observatory and Planetarium, accessed Feb 01, 2025, J A Hamilton and the Early Instruments – Armagh Observatory and Planetarium

[3] “Telescopes” Armagh Observatory and Planetarium,” accessed Feb 01, 2025, Telescopes – Armagh Observatory and Planetarium

[4] “A Brief History of Weather Observations at AOP,” Armagh Observatory and Planetarium, accessed Feb 01, 2025, A Brief History of Weather Observations at AOP

[5] “Recording the weather since 1794,” Armagh Observatory and Planetarium, accessed Feb 01, 2025, Recording the weather since 1794

[6] “John Louis Emil Dreyer,” Armagh Observatory and Planetarium, accessed Feb 01, 2025,John Louis Emil Dreyer – Armagh Observatory and Planetarium

[7] “The decline of scientific research in the early 20th century in Ireland,” Armagh Observatory and Planetarium, accessed Feb 01, 2025, The decline of scientific research in the early 20th century in Ireland – Armagh Observatory and Planetarium

[8] “The Rebirth of Irish Astronomy,” Armagh Observatory and Planetarium, accessed Feb 01, 2025, The Rebirth of Irish Astronomy – Armagh Observatory and Planetarium

[9] “Southern Hemisphere Astronomy and the ADH Telescope ” Armagh Observatory and Planetarium,” accessed Feb 01, 2025, Southern Hemisphere Astronomy and the ADH Telescope – Armagh Observatory and Planetarium

[10] THE ARMAGH-DUNSINK-HARVARD TELESCOPE: FROM DREAM TO OBLIVION C. J. BUTLER The Armagh-Dunsink-Harvard Telescope:

[11] “Professor Ernst Julius Öpik”, accessed Feb 01, 2025, Professor Ernst Julius Öpik – Armagh Observatory and Planetarium