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Below him will lie the great mirror, like a pool of still black water dimly sprinkled with stars. Around him will flow the starlight, down to the mirror and up to the "prime focus" of the telescope (see drawing), a rectangular hole in a tablelike structure in front of him.
Hubble will know how to find the tiny bit of sky he wants to photograph. He will telephone instructions to an assistant down at the control desk; the massive telescope will swing almost silently. When Hubble is satisfied that it is pointed right, he will put a plate in the holder, watch through a microscope, and make careful minor adjustments while the scattered photons of nebula light (some of which have been traveling for a billion years) make their marks on the photosensitive emulsion.
The plate, when Hubble develops it, will not look like much: only a few faint smudges of silver granules on a film of gelatin. By itself, the first photograph may prove little, but there will be many others. Added together, they may tell man things about his universe that have puzzled him since he came here to live.
*A light-year is the distance that light, traveling at 186,000 m.p.s., covers in one year—5,865,696,000,000 miles. *Dr. Vesto Slipher of Lowell Observatory measured, before Hubble, the slower speeds of nearer nebulae. *Hubble would be the first to deny that all the credit for the expanding universe theory is his. Many others, from Harvard's Harlow Shapley to Belgium's Abbe Georges Lemaitre, have contributed. *One cause for coolness: a studio, planning a movie about the stars, hired a Mount Wilson astronomer as consultant. He was happy with his easy $200 a month until he discovered that the studio had also hired an astrologer—at $1,500. *Humason alone is pessimistic. Thinking of his mercury-spoiled spectrographs, he says gloomily: "You don't know southern California." *The first thing the great eye reflected when set on edge was a row of pin-up girls on the wall of the optical shop.