Total Solar Eclipse of 1955 June 20
from the Noratlas (N 2501) flight out of Saïgon-Tan Son Nhùt
With a duration of 7 minutes and 8 seconds at its maximum in the China Sea, the 1955 June 20 total solar eclipse was the longuest of the XXth century, before the 1973 June 30 with the Concorde 001. The French scientific community, including Raymond Michard† of the Paris-Meudon Observatory, tried during the Indochina war to prepare the observation of this eclipse from Vietnam. After the end of the Indochina war and the partition of Vietnam in July 1954, an eclipse flight aboard a modified Noratlas 2501 could take place. In November 1954, the Secretary of State for Air decided to provide to the Bureau des Longitudes a Nord 2501 transport aircraft, capable of exceeding 8,000 meters above sea level and having the structure permitting the installation of astronomical instruments. The implementation of this decision required the assistance of a large number of people and services in the State Secretariats of the Armed Forces. Civilians and military personnel have given, often in spite of the most serious concerns, tireless attention to the success of the scientific mission. In April 1955, a Nord 2501 leaving the factory underwent at the initiative of the Technical and Industrial State Secretariat for Armament, the necessary transformations for mounting the instruments; openings in the top of the hull were drilled by engineers and technicians from the S.N.C.A.N. and the Air Force provided the crew for the eclipse flight. The last Noratlas of the French forces in Indochina left their bases on 1955 June 9th, but the specially modified Noratlas 2501 left Paris on June 8th to arrive a few days before the eclipse and execute the observation flight. Three observers were aboard: two astronomers from the Paris-Meudon Observatory, Raymond Michard† and Michel Trellis, and one officer from the French Air Force Scientific Bureau, the Lieutenant Colonel Gallavardin who oversaw the whole mission from the beginning. The Japanese from the Tokyo Astronomical Observatory have viewed succesfully the eclipse from the seashore at Ha-Hap in the Kikuik Bay, South Vietnam.
Three photographic chambers were used to photograph the different regions of the solar corona.
Installation of instruments
About ten minutes before the arrival of the umbral shadow cone, the aircraft was flying due East along the centerline off the coast east of Vietnam at an altitude of 26,500 feet (8,100 meters). Below the aircraft, at an altitude of about 4 to 5,000 meters, there was a sea of clouds. Above the sky was unfortunately not completely clear as there were cirrus of irregular density; it was far from "coronal". As a relatively unobstructed area had been reached, while in front we could see thicker upper layers, the pilot executed a loop to wait on the spot for the umbral shadow of the Moon and at the exit of the turn it was onto the plane. Due to the displacement of the aircraft in the same direction as the Moon’s shadow, the totality duration lasted 8 minutes, that is approximately an additional minute compared to a stationary observer. Despite a mechanical failure on one of the photographic chambers, 16 images were obtained. Due to overexposure and aircraft movements during the poses, these documents do not have the usual appearance of eclipse plates: the image of the Moon is gone and the inner corona is formless! Only the outer corona that has no delicate structure can be studied.