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In focus

A nebula of papers

by Louisiane Ferlier

From the archives to space, Louisiane Ferlier dives into the papers Caroline, William and John Herschel created when observing nebulae and searching for comets.

The digitisation of the nebulae papers was made possible thanks to the generous donation of the John S. Cohen Foundation.

Somewhere, orbiting indefinitely between the Sun and the Earth, you will find the decommissioned Herschel Space Observatory. The image of the Horsehead nebula (Barnard 33) in the constellation of Orion you will see at the top of this article was captured using the Herschel telescope, which was launched in 2009 by the European Space Agency (ESA). In every way, this image builds on the work started closer to home, by another Herschel telescope in the 1780s.

The astronomical work of Caroline, William and John Herschel is well-known and celebrated, from the discovery of Uranus, galaxies and comets. But what I would like to focus on here is the patient hours three generations of Herschels spent observing nebulae.

‘Nebulae’ was the term used in the eighteenth century to qualify celestial objects outside our solar system, with a diffuse, hazy quality. We now know them to be clouds of gas or dust. In 1771, the French astronomer Charles Messier published a first catalogue locating and identifying 45 nebulae. Caroline Herschel, during one of her sweeps for comets on her 40-foot telescope, noted objects which were absent from Messier’s catalogue. Caroline and her brother William then set out to systematically look for and locate additional nebulae, or ‘island universes’ as William called them.

The process was highly choreographed, iterative and often collaborative: the Herschels would sweep the skies with the telescope, then note down results, carefully indicating the locations, describing the objects and any other relevant observations. They would cross-check positions in existing celestial maps such as Flamsteed’s Historia Coelestis Britannica.

Orion and Taurus constellations, map 2, John Flamsteed, Atlas coelestis, 1729.
Royal Society printed collections.

The results were later tabulated, and the Herschels created an indexing system, still used as an astronomical reference today, to name the objects observed in the night sky. Science in the Making contains for the first time archival documents from every stage of that process.

First the registers, which read like diaries of the Herschels’ nightly sweeps:

Registers of nebulae

They reveal the collaborative aspect of their scientific process. For example, William wrote on 23 September 1783:

‘My sister has found a new Nebula. Its situation is not easily described since Flamstead [sic] has not given us one star in that part of the heavens to delineate its situation by.'

The raw observations were later turned into indexes or catalogues, with their rows locating the objects and making neat what may have been a frustrating sweep due to clouds or poor optical resolution.

Finally, the results were submitted for publication to the Royal Society. William Herschel published the first 'Catalogue of nebulae and clusters of stars' in the Philosophical Transactions in 1786 locating a first set of 1,000 celestial objects. Three years later, the total would double and by 1802 they would reach 2,500.

Catalogues of nebulae

Published catalogues of nebulae

Caroline Herschel’s meticulous work to revise Flamsteed’s reference book would be published as a separate monograph by the Royal Society and its related archive can be found at the Royal Astronomical Society.

This astronomical cataloguing endeavour was pursued by John Frederick William Herschel, William’s son and a scientific giant himself. From Cape Town, South Africa, where he resided for five years, Sir John added to the observations of the Northern skies made by his aunt and father to create a picture of the celestial bodies visible from the Southern hemisphere.

His work was published in 1864 as the ‘General Catalogue of nebulae and Clusters of Stars’ which would double the number of his father’s observations, bringing the total to 5,079. Finally, after his death, a General Catalogue of 10,300 multiple and double stars would testify to the progress of telescopes in less than a hundred years and the importance of creating a global network of observatories.

In addition to augmenting the astronomical record of his aunt and father, Sir John also enriched the Royal Society collections by depositing the archival treasure trove as he was finishing the process of publishing his own nebulae catalogue. In his diary for 4 October 1863, he writes:

‘Added the final sentences to the introduction of my nebulae catalogue and prepared a letter for Stokes [George Gabriel Stokes, then Secretary of the Royal Society] presenting my Father’s sweeps and Register sheets & my Aunt’s catalogue to R.S.’

The manuscripts in the Royal Society collections represent eighty years’ worth of observational and research effort by successive generations of the Herschel family to record, classify and publish the locations of nebulae, galaxies, globular clusters and other astronomical objects. For the Royal Society, the product of this monumental effort was only four published papers: but it is worth noting that many observations were published in the Memoirs of the Royal Astronomical Society and elsewhere.

The records themselves are fascinating archives of science as it is being made. They make visible the intimate relationship with the telescope, through their sheer volume, and the drudgery needed to translate scientific observation to finished catalogue. They also remind us of the important contribution of the first female professional astronomer, Caroline Herschel, which is sometimes hidden in the pages and because of, as she wrote herself, ‘how dangerous it is for women to draw too much notice on themselves’.

This brief venture through the nebula of Herschel papers certainly reveals how central astronomical activities were to the family. Indeed, Sir John’s son, Colonel John Herschel, would continue to observe nebulae from South Africa and India. With so much work done by the Herschel family to observe, map, classify and index celestial objects, I hope you will agree that it was only right that an instrument sent to space 200 years later, should write their names in the sky.

Fellows of the Royal Society mentioned in this article:

Caroline Lucretia Herschel

About the Author:

Dr Louisiane Ferlier is the Digital Resources Manager for the Royal Society collections. She has been working on Science in the Making since its inception when she joined the Society in 2015 to manage the digitisation of its historical journals. She previously held positions at the University of Oxford and the Centre for Editing Lives and Letters at UCL, specialising in the history of ideas, books, archives and libraries.