When 15th-century European navigators first sailed south of the equator, they watched nervously as the North Star sank below the horizon. What new dangers, they wondered, would the southern seas hold? And how would they navigate without the familiar northern stars?
The dangers of the southern seas were real enough. But the stars of the Southern Cross served as a good omen to Christian navigators, and they pointed the way to the south celestial pole. In time navigators learned to find their position using many other bright southern stars, as well as the Sun and planets.
By the late 16th-century, Dutch navigators Pieter Keyzer and Frederick de Houtman, and the astronomer Petrus Plancius, created new southern constellations based on exotic creatures encountered on their travels (Tucana, Pavo, Dorado), or mythical beasts (Phoenix, Apus). These constellations were included on Johann Bayer’s epic star atlas Uranometria in 1603 and remain in use today.
But vast swaths of deep-southern sky remained unnamed until the mid-18th century when the industrious and austere French astronomer, Nicolas Louis de Lacaille, during a scientific expedition to South Africa of astounding range and productivity, produced the most rigorous and detailed southern sky survey for the next hundred years.
A Man Smitten by Mathematics and Astronomy
The son of a prosperous and respected family, Lacaille (pronounced “la-KAI”) was born March 15, 1713 in Rumigny, France, near the Belgian border. His father had a flair for mechanics, invented a number of industrial machines, and supported his family through positions appointed by the Duke of Bourbon. Nicolas studied classics, philosophy, and theology. When his father died suddenly, 19-year-old Nicolas was left without means to continue his studies. But the Duke recognized the young man’s ability and seriousness of purpose and continued to support him.
Lacaille planned to become a priest. But he was smitten by mathematics and astronomy, which he began to study privately. He finished his theology degree but had no taste for further religious study. Instead, as a self-taught astronomer, he was recommended in 1737 for a position at the Paris Observatory with Jacques Cassini. Here Lacaille honed his skills and applied them to the science of geodesy. He helped map the French Coast from Nantes to Bayonne and took a leading role in measuring the great meridian of France, proving the Earth was an oblate spheroid, somewhat wider across the equator than the poles.
A Plan to Map the Southern Skies
Lacaille’s work gained him election to the Royal Academy of Sciences in Paris and a post at the College Mazarin where he established a small observatory, made systematic observations of star positions and parallax, and wrote widely-read texts on mathematics, astronomy, and optics. By his late 30’s, Lacaille had established a solid reputation and earned a comfortable life as an academic. But he sought a new challenge, and found it in the southern heavens. He successfully proposed to the Academy an expedition to the Cape of Good Hope to catalog the southern sky and undertake geographical measurements of the area. On November 21, 1750, Lacaille embarked on the ship Glorieux, heading first to Rio de Janeiro for repairs, then tacking east again to South Africa.
On April 19, 1751, Lacaille landed at Cape Town, then a small waystation of the Dutch East India Company. He carried a letter of introduction from the Dutch Prince of Orange, was received warmly by the Dutch governor, and lodged at the home of Jan Bestbier on what is now Strand Street. The Dutch found the French astronomer somewhat reserved but amiable, and gave him what help and materials they could. In the backyard of Bestbier’s home, Lacaille oversaw the construction of a 12-foot-square observatory for his instrumentation, which included a number of telescopes including a 14-foot-long refractor for observing the moons of Jupiter, which were then used as celestial timepieces for determining longitude.
On August 6, 1751, Lacaille set to work charting the southern stars. Constant southeast winds made for poor seeing in his 14-foot telescope, and Lacaille found he obtained the most accurate star positions with an 8x, 26-inch-long refractor with a ½-inch objective. With this tiny instrument, he measured the sidereal time at which stars near the meridian drifted into and out of a reticle placed in the field of view. The average of these times gave a star’s right ascension. The difference was related to its declination.
Lacaille had promised the Academy a survey of all southern stars brighter than 3rd or 4th magnitude, a population of some several hundred stars. He over-delivered. Over the next 11 months, during 110 observing sessions of 8 hours each and 16 dusk-to-dawn marathons, and despite suffering headaches, rheumatism, and fevers associated with his work, Lacaille mapped 9,766 stars as faint as 8th magnitude between declination -23 degrees and the south celestial pole. It was an astonishing feat of personal industry and endurance. In comparison, Edmund Halley, no slacker himself, mapped just 341 stars from the island of Saint Helena from 1676 to 1678.
Constellations of the Enlightenment
During his survey, Lacaille also cataloged 42 non-stellar objects including the Jewel Box Cluster, the Eta Carinae Nebula, and the globular clusters 47 Tucanae and Omega Centauri. Lacaille’s list of southern object predates the more famous catalog of his countryman, Charles Messier, by some 30 years. With his tiny telescope, Lacaille was unable to determine the nature of these objects. But he wrote to the French Academy that they were “… so varied that their exact and detailed description can occupy astronomers for a long time and give rise to a great number of curious reflections on the part of philosophers.” Lacaille himself refrained from such reflections, content to tend to his measurements.
This prodigious celestial bounty created a new problem for Lacaille: where to put it all. Much of the deep-southern heavens, especially the dim regions near the south celestial pole, were not yet demarcated into constellations. So Lacaille invented his own. As Lacaille was a man of the Enlightenment, and unencumbered by whimsy, he named his new constellations after the tools of art and science: Telescopium, the Telescope; Reticulum, the Reticule; Octans, the Octant, Fornax, the Chemist’s Furnace, and so on (see inset). His one exception was the constellation Mons Mensa (Table Mountain), now simply Mensa, which he named after the famous landmark near Cape Town. Mensa remains the only constellation named after a geographical feature. Lacaille’s 14 new constellations were called:
- Sculptor, The Sculptor’s Workshop (l’Atelier du Sculpteur)
- Pyxis, The Mariner’s Compass (la Boussole)
- Caelum, The Chisel (les Burins)
- Pictor, The Painter’s Easel (le Chevalet et la Palette)
- Circinus, The Geometer’s Compass (le Compas)
- Norma, The Carpenter’s Square (l’Equerre et la Regle)
- Fornax, The Chemist’s Furnace (le Fourneau)
- Horologium, The Clock (l’Horloge)
- Antlia, The Air Pump (la Machine Pneumatique)
- Microscopium, The Microscope (le Microscope)
- Mensa, Table Mountain (Montagne de la Table)
- Octans, The Octant (l’Octans de Reflexion)
- Reticulum, The Reticle (le Reticule Rhomboide)
- Telescopium, The Telescope (le Telescope)
It is a small wonder that astronomer Heber Curtis of Lick Observatory, upon first seeing the deep-southern sky, said, “It looked like somebody’s attic”.
An Overland Trek to Measure the Earth, and More
While at the Cape, Lacaille also precisely measured the positions of the Moon, Venus, and Mars with respect to the background stars. Upon his return to France, he compared his measurements to those made in Germany on the same dates by his colleague Joseph de Lalande. The slight difference in angular position of these objects caused by parallax allowed Lacaille to estimate the distances to the Moon and Sun. Lacaille and Lalande also compared positions of stars low on the horizon in France and high overhead in South Africa to estimate the effects of atmospheric refraction as a function of temperature and pressure.
His celestial survey complete, Lacaille turned to his next major goal: measurement of the arc of the meridian near the Cape. With the help of the governor, and with a translator, he surveyed three quarters of a degree in a north-south direction, a punishing task in unfamiliar, mountainous countryside and without a working knowledge of Dutch.
Surprisingly, Lacaille concluded the meridian to be 1000 feet longer in the southern hemisphere than the north. In essence, he showed the Earth was slightly pear-shaped. It turns out Lacaille made an uncharacteristic oversight: he failed to account for the gravitational influence of Table Mountain, which caused a deviation in a plumb bob sufficient to account for his result. Newton’s Law of Gravitation predicted this effect, and historians have long debated why Lacaille neglected it. Some say Lacaille, a Frenchman, may have had an unconscious reluctance to apply the theory of an English scientist. Others thought it was an honest oversight. No one knows for sure.
Before he left the Cape, Lacaille also measured the longitude of Cape Town using Jupiter’s moons, kept tide and weather records, and measured the height of Table Mountain. He also collected and shipped back to the royal gardens in France shells, plants, rocks, and even the skin of a wild donkey. It is small wonder Sir David Gill, a distinguished 19th-century director of the Cape Observatory, said of Lacaille’s time in South Africa, “this was one of the most remarkable, successful, and useful scientific expeditions ever undertaken”.
The Return to France and an Early Demise
Lacaille returned to France, with a 9-month detour to survey the French islands of Mauritius and Réunion in the Indian Ocean. In his journal, he notes his indifference to these tropical paradises and his fond wish to return to France to continue his work. He finally arrived in Paris on June 28, 1754 after an absence of three years, eight months.
Lacaille was greeted in France as a scientific hero, a “star returning to the horizon”. This was the long lost Age of Reason when scientists were as celebrated as the movie stars of today. But the modest Lacaille would have none of it. He refused fanfare and trappings of fame, wishing only to return to his observatory at the College Mazarin.
With a small pension from the Academy, Lacaille resumed work. He produced detailed star maps of the southern heavens, presenting to the Academy in 1752 an engraving showing naked-eye stars and his fourteen new constellations. While not shown on the engraving, Lacaille also split the largest constellation Argo Navis (The Ship of the Argonauts) into the three smaller constellations Puppis (The Deck), Vela (The Sail), and Carina (The Keel). Lacaille included his new constellations in his catalog Coelum Australe Stelliferum, which served as the basis for Jean Fortin’s widely read Atlas Celeste in 1776. Lacaille’s constellations remain in use today.
From 1756 through 1761, Lacaille precisely measured zodiacal star positions, edited his textbooks, published his table of atmospheric refractive index, and issued a report on the appearance of the Comet of 1759 (now called Halley’s Comet). He wrote an early draft of his travel memoirs Journal Historique. He also managed to reduce 1,942 of his 9,766 measurements of star positions. The rest were compiled in Edinburgh in the 1840’s by Thomas Henderson, who published the full list in 1847 as A Catalogue of 9766 Stars in the Southern Hemisphere.
Lacaille dreamed of returning to observe the southern heavens. He did not get the chance. Twenty-seven years of hard work and long nights at the telescope took their toll. In early 1762, symptoms he suffered in South Africa returned: headaches, nosebleeds, fever, and digestive problems. Dutch doctors at the Cape had helped Lacaille, but Parisian doctors could not. He died on March 21, 1762 at the age of 49.
Of Lacaille, it was said he made more observations and calculations than any other scientist of the day. It may be true, especially over his relatively short career. Lacaille was no Isaac Newton, or Pierre-Simon de Laplace. And he was not given to public speculation as to the nature of his observations, as was William Herschel a few decades later. Instead, Lacaille was a data collector of the highest order at a time when science required this kind of work. His results enhanced navigation, geodesy, and astronomy. And they set the stage for later astronomical expeditions to South Africa in the mid-19th century by John Herschel and Thomas Maclear.
Lacaille could have accomplished even more. But he suffered the great regret of many northern stargazers who travel to the southern hemisphere: he should have brought a bigger telescope. John Herschel, who brought a much better instrument to South Africa in 1847, is rightly credited with the discovery of hundreds of deep-sky objects in the southern heavens. Had Lacaille been better equipped, he would have earned credit for these discoveries and advanced knowledge of the southern heavens by nearly 100 years.
Still, Lacaille is sometimes called the “Father of Southern Astronomy”, especially in South Africa where he is held in high regard. Unlike the Herschels, or Charles Messier, he is not well known today, perhaps because he caused little controversy, shunned fame, and died relatively young. But fame was not his goal. Indeed, as David Evans, his most recent biographer, said of Lacaille, 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.”