Solar Eclipse, May 28, 1900
Photograph of Corona, by Harrison W. Smith
From Technology Review, vol. 2, no. 3, July 1900
In May 1900 a small group from MIT boarded a southbound steamer for Savannah and proceeded from there by train and mule car to Washington, Georgia, to observe a total eclipse of the sun. Alfred E. Burton (Professor of Civil Engineering and later Dean of Students), who led the expedition, chose Washington after careful weighing of such factors as probability of cloud cover and probability of comfort in available hotel accommodations. Other southern localities hosted other groups, but MIT's choice seemed appealing to many, and the Tech men were soon joined by observers from Harvard, the Blue Hill Observatory, and the Flagstaff Observatory. Burton's account in Technology Review reveals that the visitors from Tech thoroughly enjoyed afternoon teas, a farewell "Georgia cue" (i.e., barbecue), and other amenities in addition to their busy preparations for the much-anticipated May 28 astronomical event.
Photograph of Smith and his camera from Technology Review,
vol. 2, no. 3, July 1900,
p. 209A total eclipse of the sun occurs somewhere on earth when the sun, moon, and earth are in alignment. When the moon's umbra (a conelike shadow created when the moon passes between the sun and earth) touches the surface of the earth, a total eclipse can be observed at that position and at all points within the umbra's narrow path (never wider than two hundred miles) as it races across the earth's surface at approximately one thousand miles per hour. A given location on earth experiences total eclipse for only a few minutes once every three hundred years.
The photograph shown above was taken by Harrison W. Smith (an assistant in physics at MIT), using a camera custom-made from a long wooden box and a lens borrowed from a telescope with an aperture of three inches and focal length of 43 inches. The camera's base was mounted on posts tilted to be parallel with the plane of the earth's equator. To minimize blur from the apparent movement of the sun during each ten second exposure, the apparatus was equipped with a hand-operated crank, attached to gears and a tangent screw, allowing the camera to rotate by regular adjustments. Smith's hand turned the crank at a rate governed by the beat of a carefully calibrated metronome. The bold fringe of light surrounding the black disk of the moon in shadow is known as the sun's corona. It is always present, but never seen unless the sun's brightness is obscured by an eclipse.
The next total eclipse of the sun visible in the United States will be on August 21, 2017. When will a total eclipse cast its shadow on your home town? Check an astronomer's predictions. Information about other eclipses and how they were studied by researchers and students from MIT can be found in the papers of physicist and astronomer Harlan True Stetson (MC 392) in the Institute Archives, 14N-118.
Object of the Month: May 2000, May 2010