The stereoscopic effect depends on the fact that the two eyes see a scene from slightly different viewpoints. The distance between the average adult's eyes is about 7.5 cm, and objects as far away as 300 m can be perceived stereoscopically with pictures taken with a stereo camera that has its two lenses separated by this amount. However, to make a stereoscopic picture of the moon, the two pictures must be taken with two lenses about 100,000 kilometers apart.

   Charles Wheatstone (1802-1875), who wrote the first paper on the stereoscopic effect in 1838, suggested that the librations of the Moon be used to obtain the necessary baseline. The principal libration, or apparent rocking back and forth of the moon, results from the fact that the moon travels in an elliptical orbit around the earth while spinning at a constant rate about its axis. Even though the same face of the moon is always presented to the earth, 59% of its surface is visible at one time or another. Thus, pictures taken at different times can be viewed in a stereo viewer; the moon looks something like an orange suspended in space.

   All of the stereoscopic views on this page are from the Greenslade Collection.
 

This stereo picture of the moon is labelled "FULL MOON. From negatives taken by Prof. H. Draper with his silvered glass telescope. Published by C. Bierstadt, Niagara Falls, N.Y."    Draper was the Professor of Chemistry at New York University, and made the first daguerreotype portrait in the United States in 1840.

The left-hand end of this stereo pair says "From original negatives by L. M. Rutherfurd"; the right-hand end says "Published only by P.F. Weil, New York". These pictures were taken on  15 September and 13 November 1864,    Lewis Morris Rutherfurd (1816-1892) was a lawyer whose avocation was astronomy. He was best known for making the finest diffraction gratings before the time of Henry Rowland of Johns Hopkins.

The handwritten label on this stereo card of the moon reads "View of the half Moon. Original". This may be a copy of the first stereoscopic view of the moon taken by the English astronomer Warren de la Rue in November 1857 and March 1858.

The Keystone View Company of Meadville, Pennsylvania, was the largest producer of stereo views in the first quarter of the twentieth century. This stereoscopic view of the full moon is copyright by the Yerkes Observatory of the University of Chicago. This went into operation in the last years of the nineteenth century.

Here is the "Moon at the Age of Seventeen Days", or three days after the full moon of the last picture. The back of this Keystone View Company stereoscopic view has information about the moon; these cards were part education and part entertainment. The view is copyright by the Yerkes Observatory.