A total eclipse of the sun lasts only a few minutes. Now imagine being able to observe an eclipse for 74 minutes! That’s what the members of a special team on board a prototype of the Concorde got to do in 1973.
How does an eclipse of the Sun unfold?
A solar eclipse takes place when the Moon passes before the sun, momentarily hiding it. If the Moon completely conceals the solar disc, the eclipse is then total. The rules of celestial mechanics ensure that the totality of a solar eclipse cannot last longer than 7 minutes, 40 seconds.
On June 30, 1973, a total eclipse of the Sun took place above the African continent. The totality phase was especially long: the Sun was hidden for 7 minutes and 4 seconds. A total eclipse of the Sun lasting that long will not repeat until 2150.
Using the Concorde to observe the eclipse
The Concorde, developed jointly by France and England, was the only commercial aircraft to travel faster than the speed of sound before its permanent withdrawal in 2003. The Concorde’s test flights took place from 1969 until 1975.
At that time, a young French astronomer, Pierre Léna, had a mad idea: follow the shadow of the Moon with the prototype of the Concorde supersonic aircraft that was in trial phase. You have to know that the Moon’s shadow, the umbra, projected on Earth moves at a speed of at least 2,162 kilometers an hour. The Concorde, meanwhile, could fly at 2,500 kilometers an hour. Léna therefore hoped to observe the eclipse for over 70 minutes – in other words 10 times longer than could be done on the ground.
In May 1972, Léna convinced André Turcat, the principal pilot assigned to Concorde trials, of the feasibility of the project. Authorization was given in February 1973.
Decking out the Concorde for scientific experiments
Five scientific experiments were to be carried out during the flight, in which eight astronomers, including Pierre Léna, would be on board. To that end, four portholes had to be drilled in the plane’s roof to allow cameras to record the eclipse. Léna observed the solar corona (a region of diffuse gas surrounding the Sun and visible only during eclipses) in infrared light, an area of astronomy that was expanding at that time.
The Concorde followed a direct-course line in the Moon’s umbra, which was overflying Sahara, Mauritania, Mali, Nigeria and Chad. Mauritania at first refused the flight over its territory, closing its airspace the whole day of the eclipse. Many amateur astronomers were on hand to experience the celestial phenomenon. Finally, Mauritian authorities authorized the Concorde to fly during the solar eclipse.
A historic flight
The aircraft took off from Las Palmas airport in the Canary Islands at 10:08 a.m. on June 30, 1973. At 10:53 and 14 seconds, at a speed of 2,519 kilometers an hour and an altitude of 17,000 meters, Concorde 001 entered the Moon’s shadow. André Turcat and his crew demonstrated very great flying skills, making the rendezvous at exactly the right second and down to the nautical mile.
The aircraft enjoyed perfect stability during the flight, enabling the astronomers to perform all the experiments without incident. The altitude reached by the Concorde among other things made it possible to observe the neighborhood of the Sun in infrared light.
Concorde 001 left the Moon’s shadow at 12:07 and 13 seconds, after spending 74 minutes in the darkness of the solar eclipse, a record for the duration of solar-eclipse totality unequaled to this day.
The aircraft touched down at Fort-Lamy (today N’Djamena) in Chad at 12:56 p.m.
An eventful return
Crew members were surprised to see quite a number of soldiers and tanks in the city streets following the flight. They learned afterwards that a coup d’état attempted during the eclipse had failed.
As Pierre Léna would later modestly recognize, the results of the experiments conducted during this historic flight were useful, but not to the extent of revolutionizing our scientific knowledge.
Yet the fact remains that this Concorde flight allowed us to observe the longest total eclipse of the Sun in history.