Lacaille at the Cape of Good Hope
16 Oct 2018
Lacaille 8760 is the brightest red dwarf in Earth’s sky. Lying in the constellation Microscopium, this 6.69 magnitude red dwarf honours a truly remarkable French astronomer – Nicolas-Louis de Lacaille (1713-1762) – the man who literally lived and died for the stars. During his working life, he made more observations and calculations than all of his peers put together, and he died one week after his 49th birthday from the rigors he suffered observing the sky, or as Patrick Moore put it “… burned out by the intensity of his intellectual fire”.
Indeed, his astronomical achievement alone during his two years at the Cape of Good Hope (1751-1753) was incredible, especially when we take into account that he completed his observations over one year, getting in 126 observing nights owing to the Cape’s weather which he categorised thus: “one fifth was cloudy, one fifth was variable, one fifth was calm and clear, and the remaining two fifths were clear with a strong, south-easterly wind that blew from September to March.”
Using an absurdly small 1/2-inch refractor (8x magnification), he measured the positions of an astonishing 9,766 stars; logged 42 deep sky objects including among others, 47 Tuc, Omega Centauri, the Tarantula Nebula, and the Eta Carinae Nebula; filled the un-mapped regions of the southern sky with 14 new constellations (placing 1,000 stars in them); gave precise boundaries to the earlier constellations; restored stars swiped by Edmond Halley from the enormous constellation Argo Navis to form the obsequious constellation, Robur Carolinum, Charles’s Oak, (it commemorated the oak tree in which King Charles II hid after his defeat by Oliver Cromwell’s republican forces at the Battle of Worcester in 1651) – to their rightful owner; and then he dismantled the enormous Argo Navis. In the notes to his catalogue he wrote: ‘I have divided [Argo Navis] into three parts, namely la Pouppe [Puppis], le Corps [Carina] & la Voilure [Vela]’.
And he has the distinct honour of being the first person to systematically observe the whole sky!
Yet despite being described by Sir David Gill as “one of the most earnest and active astronomers that ever lived…. he laid the foundations of sidereal astronomy of the Southern Hemisphere; he did that great work in a single year at Strand Street, Cape Town” Lacaille remains curiously obscure. His biographer, David Evans, wrote that he “lived for science and nothing else. In none of the accounts does he ever appear as a definite personality; he has few friends and no emotions. He seems a man without a private life who appears to pour forth the flood of his researches and disappears into an obscurity in which those researches are at once the only light and the only memorial.” (But he did love his dog! Indeed, he had a skilled instrumentalist called Poitevin but he doesn’t mention anywhere that Poitevin assisted him at night, whereas he does acknowledge the companionship of Gris-Gris, a dog that he had picked up at the start of his voyage south.)
Indeed, to the extent that Lacaille is known today, it is primarily for the 14 constellations he added to the southern sky. But, oh my, his wonderfully odd collection of a pendulum clock, microscope, telescope, geometer’s compass, chemist’s furnace, octant, engraving tool, ship’s compass, carpenter’s square, air pump, reticle, sculptor’s workshop, painter’s easel, and mountain tell us a lot about the man. All but the mountain honoured instruments that symbolised the Age of Enlightenment, the intellectual and philosophical movement that dominated the world of ideas in Europe during the 18th century, illuminating human intellect and culture after the dark Middle Ages. Reason, liberty and the scientific method… what else would a man who lived for science and nothing else put into the sky? And for us astronomy-lovers who have followed… what a fabulous way to honour the movement that wrenched human thought out of the wrong kind of “dark”.
Lacaille’s mountain… Mons Mensa (later simply Mensa), Cape Town’s Table Mountain… albeit a majestic and imposing mountain that dominates Cape Town, it seems an anomaly among all his fabulous instruments, and I have often wondered at what seems to me a charmingly romantic whimsy of putting it among the stars.
The inimitable Richard Hinckley Allen in his wonderful 1899 book, Star Names – Their Lore and Meaning wrote, “La Caille, who did so much for our knowledge of the southern heavens, formed the figure from stars under the Greater Cloud, between the poles of the equator and the ecliptic, just north of the polar Octans; the title being suggested by the fact that the Table Mountain, back of Cape Town, ‘which had witnessed his nightly vigils and daily toils,’ also was frequently capped by a cloud”. Indeed, Table Mountain is famous for its orographic cloud formation that lies over the top of the mountain “at the approach of a violent south-easterly wind” (“à l’approche d’un vent violent de sud-est”), as Lacaille put it, and he was very taken with it. He gave Mensa the appearance of being capped by the white cloud like its terrestrial namesake by incorporating part of the misty Large Magellanic Cloud into the new constellation.
Lacaille’s star chart depicting his 14 new southern constellations first appeared in the Mémoires of the Académie Royal des Sciences, oddly dated 1752 but actually published in 1756. A second edition of Lacaille’s planisphere was published in 1763 in Coelum Australe Stelliferum. This copy below of the planisphere is from Jean Fortin’s Atlas Céleste, first published in 1776, and gives constellation names in French, as did Lacaille’s original. Interestingly, although Lacaille subdivided Argo Navis into Puppis, Carina and Vela in his accompanying catalogue, he still depicted it as a unified figure on his chart (le Navire). Also interesting, he depicted Keyser and de Houtman’s Triangulum Australe with an attached plumb line.
And then there is the magnificent planisphere of the southern sky painted by Lacaille’s friend, Anne-Louise Le Jeuneux, in 1755, after his drawing. They were evidently close friends, for Lacaille asked after her in a number of his letters home from the Cape of Good Hope, sending his best wishes.
Lacaille’s observatory was erected in the courtyard adjoining the house at 7 Strand Street that a leading citizen, Jan L. Bestbier, put at Lacaille’s disposal when he arrived at the Cape on April 20, 1751. (The house was near the shore of Table Bay.) The governor, Ryk Tulbagh, helped with the building of the observatory. It was a 4.1 meter square with the corners pointing north, east, south and west, and Lacaille described it as “at the bottom of the court of the house where I stayed, on a raised area of 7 or 8 feet above the level of the sea”. It appears that Lacaille worked alone at his nightly vigils for although he had a skilled instrumentalist named Poitevin, a pupil of Claude Langlois (the most highly regarded maker of scientific instruments in France), nowhere does he state that Poitevin assisted him at night, whereas he does mention the companionship of Gris-Gris, a stray dog that he had found abandoned on the quayside at the start of his voyage south.
It was here that he compiled his star catalogue. Lacaille’s aim was to replace the catalogue of 341 stars made by Halley in 1677 (observing on the island of St Helena) with a better one, which he most certainly did with his 9,766 stars! Of these stars, Lacaille himself reduced the positions for only 1,942 of them for a preliminary catalogue, Coelum Australe Stelliferum, published posthumously in 1763. The remaining stars were reduced in 1844 and published under the direction of Francis Baily as A Catalogue of 9766 Stars in the Southern Hemisphere in 1847, 85 years after his death. Mr Wallace, Assistant Astronomer of the Royal Observatory, Edinburgh, did the reductions, and John Herschel wrote the preface.
While determining the position of stars for his catalogue, Lacaille also noted the positions of 42 nebulous objects, and his catalogue Sur les Étoiles Nébuleuses du Ciel Austral (On the nebulous Stars of the Southern Sky) was published in 1755 in the Memoirs of the Academie des Sciences. In the catalogue he divided the 42 nebulous objects into three types: ‘Nebulosities not accompanied by stars’, ‘Nebulosities due to clusters’, and ‘Stars accompanied by nebulosity’. There are 14 objects in each part. Today the objects are classified as 23 open clusters, 7 globular clusters, 4 diffuse nebulae, and one galaxy. The other 7 objects are asterisms or stars. (Interestingly, Messier later included seven of Lacaille’s objects in his famous catalogue – namely, M4, M6, M7, M8, M22, M55 and M83.)
In his report to the Academie des Sciences, Lacaille described his three nebulous types thus: “I first observe that three kinds of nebulae can be distinguished in the heavens; the first is no more than a whitish, ill-defined area, more or less luminous and of a very irregular shape: these patches are quite similar to the nuclei of faint, tail-less comets.
“The second class of nebulae comprises Stars which are only nebulous in appearance to the naked eye, but when seen in the telescope, show up as a cluster of distinct Stars, although very close to each other.
“The third class is that of stars that are actually accompanied by or surrounded with white patches or by nebulae of the first class.
“I have found a large number of these three types of nebulae in the southern part of the sky, but I do not flatter myself to think that I have observed them all, especially those of the first and third classes, because they can scarcely be seen out of the twilight and in the absence of the moon. However, believe that the list here is passably complete in regard to the more outstanding in these three classes.”
In the same report he also wrote: “The Stars that are called nebulous offer to the eyes of Observers a spectacle so varied that their exact and detailed description could occupy an Astronomer for a long time and cause philosophers to make curious reflections. As strange are those nebulae we can see in Europe, those which are in the vicinity of the southern Pole concede them nothing, either in number or form. I am going to outline here an account and a list: this essay may help those who have the equipment and leisure to study them with long telescopes. I would greatly wished to give something more detailed and instructive for this article, but, other than ordinary telescopes of 15 to 18 feet focal length, those I had at the Cape of Good Hope were not adequate or convenient for this kind of research. Those who would take the trouble to examine what occupied me during my visit to that country will easily see that I did not have time to make these kinds of observations.”
Lacaille also studied the Magellanic Clouds and wrote in the same report: “In frequent examination with a 14-foot telescope of the areas of the milky way where its whiteness is most noticeable, and comparing them with the two clouds common called the Magellanic Clouds, which the Dutch and Danes call the Cape Clouds, it is obvious that the white portions resemble one another so perfectly that one believes without too much conjecture , that they are of the same nature, or, if you like, that these clouds are no more than detached parts of the milky way, which are themselves composed merely of parts often interrupted. It is not certain that the whiteness of these parts could be caused, as is commonly supposed, by clusters of small Stars, more closely packed than in other parts of the sky, for with such attention as I have observed the better defined extremities, whether of the Milky Way or of the Clouds, I have not seen anything with the 14-foot telescope, other than a whiteness against the background of the sky , without seeing there more stars than anywhere else, where the background becomes darker.”
And his description of the Coalsack, the Southern Cross’ prominent dark nebula, in an appendix to the catalogue, is one of the first on record: “One can add among the phenomena which strike the eye of anyone looking at the southern sky, a space of about 3 degrees in every direction which seems intensely black in the eastern part of the Southern Cross. This is caused by the contrast with the brightness of the Milky Way which surrounds this space on all sides.”
Lacaille also made many other astronomical and physical observations. Adopting a new procedure involving the skillful combination of observations of the same 160 stars from both Paris and the Cape, he determined the effect of atmospheric refraction on stellar altitudes and in 1755 published improved correction tables. Making simultaneous observations with Jérôme Lalande in Berlin, he obtained the best values of his time for the parallax of the Moon, Mars and the Sun. (It was on this occasion that the nineteen-year-old Lalande made his own astronomical reputation.) Considered to be of particular importance by members of the Academie des Sciences were his experiments on the determination of longitude at sea, for which he recommended a revised procedure based on observations of the position of the moon.
He determined the longitude of Cape Town more accurately than before, by timing occultations of Jupiter’s satellites. He surveyed Table Mountain from a baseline on the beach. He determined the local magnetic elements, and made tidal observations. He also kept a daily meteorological record. A paper published in the Memoires of the academy in 1755 summarised and discussed the meteorological observations he had made during the year from 1 July 1751 to 30 June 1752. More than a century later, in 1864, Thomas Maclear considered this paper important enough to have an English translation, “Meteorological observations, or description of the winds and seasons at the Cape”, published in the Cape of Good Hope Blue Book.
After completing his main astronomical tasks in August 1752, Lacaille set about measuring an arc of meridian to determine the size and shape of the earth in the southern hemisphere. He set off on 9 September in two wagons (one drawn by six horses, the other by ten oxen) for the northern end of his chosen arc – a farm called Klipfontein (still in existence and near the small modern day village of Aurora which was founded in 1906 when the owner of the farm, P.J. Kotze, granted a part of the farm for its development). This was some 135.7 kilometres north of his Strand Street observatory, giving an arc length of 1.2°. He measured the latitude of the two sites using standard procedures, which involved a plumb line for defining the zenith, and triangulated from the tops of two mountains (Kapocberg and Riebeek Kasteel) to determine the linear distance between the sites.
The result of Lacaille’s measurements were puzzling, to say the least. From it – and he checked his figures with his habitual care – the southern half of the earth was found to be of different shape from the northern half. In fact, it appeared the earth was the shape of a pear, with a larger bulge in the southern hemisphere! The discrepancy remained a mystery for nearly 90 years, until Thomas Maclear, acting on a hint by Sir George Everest solved the mystery (Maclear and his assistants were heavily involved in the project from late 1837 to late 1847). The problem was that Lacaille measured his Arc of the Meridian between two mountains. Setting up his instruments at each end of the Arc required for them to be exactly vertical in order to measure the positions of stars for determining the latitude, but his instruments were influenced by the gravitational attraction of the mountains (Table Mountain and Piketberg). A plumb line will not hang exactly vertical next to a mountain, because the gravity will pull it off-centre. Maclear used a very particular instrument, the Bradley Zenith Sector, which allowed him to accurately make his latitude measurements in the gravitational field of the mountains. By correcting for the gravitational attraction in his calculations he proved the Earth was in actual fact, not pear-shaped.
There is a gentle irony in Lacaille’s measurements being skewed by Mensa… and I have often wondered if the plumb bob he attached to Triangulum Australe in his original star chart wasn’t to honor the simple but incredibly important tool he used in his endeavour? Personally, it seems a pity it was subsequently ditched.
In addition to all these endeavours, Lacaille’s travels and myriad other interests, recounted in his Historical Journal of the voyage made at the Cape of Good Hope (published posthumously in 1776) are incredible… Table Mountain, inland travel, botany and zoology, mapping Hout Bay, anthropology, weather, food, farming, animals, hospitality, administration, slaves and prostitution, the customs of “Hottentots and inhabitants of the Cape of Good Hope”. He collected a great number of plants, bulbs, seeds and roots unknown in Europe for the royal botanical gardens in Paris. In addition he sent a great numbers of shells, rocks, and even the skin of a wild ass to the cabinet of the royal gardens. (The now tragically extinct, but then plentiful quagga was known as a wild ass; one wonders if it was a quagga’s skin he happened upon and shipped to Europe? The quagga was a subspecies of the plains zebra, but distinguished from other zebras by its limited pattern of primarily brown and white stripes, mainly on the front part of the body. The rear was brown and without stripes, and therefore more horse-like.)
Alas for Lacaille’s obscurity, especially in Cape Town. In 1973 the building in which he resided was demolished for the Old Mutual Centre. As if tearing down this historic house and burying all that history beneath tons of insurance company concrete wasn’t bad enough, this corner of Cape Town is held to be one of the worst examples of 1970s town planning – cheerless buildings with blank facades and roads that exclude pedestrians, forcing them into a dismal underground concourse.
And to top it all, in 1903, to commemorate his achievements, the South African Philosophical Society had designed and erected a beautiful bronze plaque to be placed at 7 Strand Street. The plaque was designed by none other than Sir Herbert Baker, the English architect responsible for some of South Africa’s most beautiful buildings. In 2010 the plaque was swiped, presumably to be flogged for scrap.
Alas for philistines and thieves.
Although, let’s face it… buildings and bronze plaques have limited lifespans, whereas the red dwarf Lacaille 8760 has an expected lifespan as close to limitless as I can imagine… it will still be shining some 70 billion years after our Sun has exhausted its fuel and shrunk to a white dwarf.
There could be no better celestial memorial for a remarkable astronomer.
Copyright © Susan Young 2018