The 1750 Louisbourg Observatory

Chabert’s map of Louisbourg and vicinity

In 1746, the French frigate Le Castor dropped anchor in Chebucto Harbour (today’s Halifax Harbour). Among its crew was 22-year-old Joseph Bernard, le Marquis de Chabert de Cogolin (1724–1805), a young naval officer making his first foray into hydrographic surveying. Chabert carefully charted the harbour and approaches, producing a map so precise that, on his return to France, he was singled out for further training by the eminent astronomer Pierre Charles Le Monnier. By 1749, he was recommended for a new mission in Acadia.

The mid-18th century was a tense time in North America. Both the French and the British recognized the strategic importance of the region, with Louisbourg and Quebec forming the backbone of French defences. Louisbourg, with its military garrison and bustling trade, needed reliable navigation charts to secure supply routes and defend the fortress.

In 1750–51, the 26-year-old Chabert returned to Louisbourg with a remarkable set of instruments. These included a series of long refracting telescopes, a Gregorian reflector, Hadley’s octant, globes, celestial charts, and a three-foot quadrant fitted with a telescope. To house this equipment, an observatory was constructed, likely near the King’s Bastion.

From this temporary site, Chabert conducted astronomical observations of extraordinary accuracy, producing both maps and a detailed account of his results. His report, published in France, reveals the existence of the Louisbourg observatory and may constitute the earliest published record of an observatory in North America.

Although the observatory did not last, Chabert’s work at Louisbourg greatly advanced his reputation. He went on to make astronomical and hydrographic surveys from the West Indies to Newfoundland, though much of his career unfolded in the Mediterranean. Rising through the naval ranks to become a vice-admiral, Chabert was decorated with numerous honours before losing his sight late in life. He died in 1805, remembered as both a sailor and a scientist.

Chabert’s original map of Chebucto Harbour (Halifax Harbour)

Gregorian telescope

Was Louisbourg Really the First?

Historians disagree on whether Louisbourg deserves the title of Canada’s first observatory. Some point to Joseph Bernard de Chabert’s 1750 structure at Louisbourg as the earliest recorded use of a purpose-built astronomical station in North America. His published report, complete with measurements and instruments, supports this claim.

Others argue that because the Louisbourg observatory was temporary and dismantled soon after, it should not be considered the ‘first.’ Instead, they point to later, more permanent observatories established in New Brunswick and Quebec during the late 18th and early 19th centuries.

The debate highlights a broader question: what qualifies as the ‘first’ observatory? Is it the earliest construction, regardless of its short life, or must it be permanent and institutional? Whatever the answer, Chabert’s Louisbourg project remains a remarkable early milestone in Canadian science.