Parks Canada interpreter Duane Collins stands beside the original sundial created by William Wales and Joseph Dymond, on display at the Parks Canada Visitor Centre in Churchill, Manitoba; Detailed illustration of sundial. © Parks Canada
A transit of Venus at Prince of Wales Fort
A photo showing the transit of Venus in 2004 © Tom Van Baak
Prince of Wales Fort National Historic Site near Churchill, Manitoba, is a place that conjures up images of the Hudson’s Bay Company and the epic struggle between France and Britain over the resources of the Hudson Bay region.
But it was also one of a handful of locations in the world to which 18th century scientists travelled to observe the “transit of Venus,” when the planet Venus passed between Earth and the Sun.
Transits of Venus are rare astronomical events, with occurrences happening in pairs that come around every hundred years or so. When they occur, the planet Venus blocks out a small part of the Sun, appearing as a small black circle moving across the solar disc.
The most recent one happened in June 2004, the first of a pair in this century. The second of the pair will be visible in North America on June 5, 2012, after which another transit of Venus will not occur again until December 2117.
In 1768, Britain’s Royal Society dispatched expeditions to the furthest reaches of the world to observe and record the 1769 transit of Venus. They hoped to use the information to calculate the distance between Earth and the Sun, and also to outdo the French in this quest. Scientists travelled to locations including Norway, Tahiti, and Prince of Wales Fort, on the frigid shore of Hudson Bay.
William Wales and his assistant, Joseph Dymond, travelled to Prince of Wales Fort in 1768, a full year before the anticipated astronomical event, where they built two “observatories” in the fort’s south-east bastion from which to watch the transit. Wales and Dymond had to invent a special sundial to aid in their measurements because the sun seen from Prince of Wales Fort was too low on the horizon to register on a conventional sundial. The sundial is carved from sandstone, a stone not found in the local area but coming from a location 50 kilometres northwest of the fort. The original sundial can be seen in Parks Canada’s Visitor Centre in Churchill
After successfully observing the 1769 transit of Venus, Wales and Dymond returned home with their data, becoming the first scientists known to overwinter on the shores of Hudson Bay.
Illustration, based on an historic description, of an observatory used by William Wales and Joseph Dymond to observe the transit of Venus from Prince of Wales Fort in June of 1769; An 18th century-style map indicating their location. © Specula astronomica minima