On 1948 May 9, the island of Rebun (礼文島) in northern Japan got a peek at a splendid pearled annular solar eclipse. On this occasion it was possible to accurately measure the path position of the Moon’s antumbra and to control the accuracy of the lunar limb profile. Such observations were already executed during the hybrid solar eclipses on 1912 April 17 near Paris in France and 1930 April 28 near Camptonville in California, both eclipses belonging to the same saros 137. Japanese and American scientists collaborated to observe the solar eclipse as a Japanese historical project and this event went down in history all over the world, and since then, Rebun Island has been internationally known for astronomical science. This solar eclipse was also a unique opportunity to eventually enable relative locations on the Earth’s surface to be determined more accurately: observations could help link some of the existing geodetic surveys on two great land masses, Asia and North America. In the end it helped reveal that the accepted position of Tokyo, starting point for all geodetic surveys of Japan and Korea, was in fact some 500 meters (1,600 feet) southeast of its true position.
From the scientific papers written at the time we can retrieve the coordinates of one observing location: those coordinates were expressed in the Tokyo geodetic datum and needed to be converted first in the current world geodetic datum (WGS84) using a converter provided by the Geospatial Information Authority of Japan. On the map below one can see that the location chosen back in May 1948 was located slightly south of the centerline computed with modern tools, while the computations back then were locating it on the northern limit. The width of the path was only 1.3 kilometer (0.8 mile).
This commemorative stela was erected in 2001, 800 meters south of the place where Japanese and American scientists collaborated to observe this pearled solar eclipse with 1,500 locals. This location was supposedly on the central line, at least from the computations at the time, nonetheless in reality just slightly outside the southern limit as we compute it nowadays. The old monument, carved in a local stone, has been moved farther to the south in a shrine.
Viewing location (next to the central line computed at the time) with an erected observation monument
And now on the left hand side the same location in May 1948 looking in the opposite direction, that is north. On the right hand side a minute before maximum eclipse.
The cinematographic equipement used at the time was a Parvo type-K camera, the most 35mm camera in the world. The Parvo was a 35mm motion picture camera developed in France by André Debrie, in 1908. The camera was relatively compact for its time. The Parvo held up to 120 meters (390 feet) of film inside without the need for an external film magazine, yielding almost 6 minutes of film at the standard film rate.
Annular eclipse from Rebun Island (礼文島), Hokkaidō, Japan: beaded/perled annular sequence from 00:38 to 00:42
(courtesy of the Shōchiku Movie Studio company)
Baily’s beads simulation just south of the centerline on Rebun Island (礼文島), Hokkaidō, Japan: look at the excellent match between the movie and the simulation
(created with Solar Eclipse Maestro)
The frames below were extracted from the movie above and it does match quite well the Baily’s beads simulation. However there are a few missing features that only appear in the higher resolution simulation. A paper by Shigetsugu Fujinami† on the lunar limb profile derived from observations describes the results from the beaded annular eclipse and the equipment used. In the paper we learn that there were multiple teams, each one of them positionned at a different location. The team led by Shigetsugu Fujinami† was located at the northern limit of the path as computed at the time, but the coordinates given are in fact slightly south of the centerline and not on the northern limit as we compute it nowadays. The simulation proves this fact and leaves no doubt about it: indeed it’s impossible to match the original pictures when located at the northern limit.
Comparison of a photograph, taken at 02:50:32 from Rebun Island (礼文島), Hokkaidō, Japan, and the simulation made with Solar Eclipse Maestro
Comparison of photographs, taken at 4 seconds intervals from Rebun Island (礼文島), Hokkaidō, Japan, and the simulation made with Solar Eclipse Maestro
Cinematographic apparatus used to record the beaded eclipse
Locals watching the solar eclipse from Rebun Island (礼文島), Hokkaidō, Japan. It appears that the local population observed the eclipse through a brittle cellulose acetate film, the one we see distributed at the very beginning of the movie and that can be easily cut by hand.