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Astronomers, if they want to look at the universe in optical wavelengths, have to stay up at night when normal people are snug abed. A class in observational techniques gave me a chance to assist a real astronomer (SS) at Mount Palomar, home at that time (1976) to several of the world's largest optical telescopes. This was near the end of the photographic era, and in fact there were already photomultipliers, CCDs, and other high-sensitivity electronic devices hooked onto most of the light-gathering apertures on the mountain.

But the astronomer I was with had some plates to expose --- classic plates, thin squares of glass more than a foot across, coated on one side with a silver halide emulsion. (The Kodak Corporation kindly kept making plates for the astronomical community for many years, as a charitable way to support research.) Our plates were baked in a gas chamber a day or two before we used them, to increase their sensitivity. We loaded them in pairs, back-to-back, into special holders that bent the glass slightly to an optimum shape for the focal plane.

SS had begged, proposed, cajoled, argued, and finally won two nights on a Schmidt telescope --- essentially a camera the size of a milk tanker truck. The Schmidt we were to use had a 48-inch mirror and cleverly-shaped correcting lenses to give it a large, sharp field of view. SS's goal was to take long exposures of several clusters of galaxies, measure the average colors of their stars, and thereby prepare for more detailed observations of galactic properties. Foundational work, in other words, but nothing earthshaking (though it was undoubtedly cosmic!).

For an observatory, good "seeing" --- a crisp, clear view of the stars --- is everything. Telescopes at high altitudes have less atmosphere above them, so stars twinkle less. Domes are unheated, to minimize air currents. Major astronomical facilities are often placed at middle latitudes on the western side of a land mass, so that prevailing winds come across an ocean and thus flow as smoothly and steadily as possible. Light pollution is the great enemy, and unshielded streetlights (especially ones that put out a broad spectrum of glare) make deep sky photography impossible.

Our first night began with light cloud cover, thin enough to give hope of clearing but thick enough to prevent any useful work. The kitchenette below the dome was well-stocked with junk food, so we drank coffee and snacked and talked with the technician in charge of the telescope. He wasn't an astronomer, but rather something of a mechanic and general expert on the instrument. Observers came and went; his job was to keep the machine running smoothly and, most importantly, prevent mistakes that might cause serious damage.

A bit before midnight the clouds blew away. We slipped the first plateholder into the Schmidt and confirmed coordinates. The tech swung the telescope and rotated the dome. Faint lights glowed, deep red to preserve night vision and avoid fogging film. Through the guide scope (a respectable-sized instrument for an amateur) the star that SS had chosen to track swam into view. For half an hour, the game was to punch buttons on a control paddle and keep that star centered on the crosshairs at high magnification, so that any irregularities in the big telescope's clock drive would not spoil the photograph. This was in fact a game, not something serious --- since we all knew that for the galactic measurements SS needed to take, minor tracking errors would make no difference whatsoever. But it kept us busy, each in turn. When an exposure time had elapsed we closed the shutter, removed and flipped the holder, and repeated the process for the other side's plate on a new field of stars. Then we put that holder away and inserted the next one. So the night passed.

Dawn came and (dog-star-tired?!) we walked to the observer's quarters on the mountain, a snug white farmhouse. After a light dinner at about 6am we retired to individual bedrooms, closed the blackout curtains, and napped until early afternoon. Then came the time to develop the previous night's plates, check their quality (all turned out well), and plan the schedule of observations to make during the night to come. Ominous clouds did not bode well. We walked to other domes and visited with the astronomers there.

At the 200-inch (5 meter) Hale telescope I climbed a ladder and sat for a few minutes in the prime focus cage, a small cylinder suspended in the middle of the instrument's tube above the huge mirror. It's a high and cozy perch even for a small person. As the big scope pivots to follow the stars, the observer's seat swivels in a circle around a boxy desk-like holder for photographic plates. Reflected starlight comes up inside a hollow cylindrical post; the human's legs are squeezed around either side of it. Control buttons adjust the telescope and rotate the dome. The hardwood railing feels like old furniture, smoothed by decades of use.

The 200-inch mirror gathers about a million times as much light as a naked human eye. A few percent gets lost at each reflection; the prime focus roost and other structures inside the tube waste a few percent more. The astronomer's job is to track the heavens, change plates, and be patient. By the 1970s the prime focus cage was rarely used: alternative light paths, better for electronic sensors, relied on arrangements of secondary mirrors to bring photons out the side or back of the telescope. It's more efficient --- but far less romantic than sitting quietly in a nest while starlight, from halfway across the universe, comes up between one's knees and strikes tiny crystals of silver salt.

SS and I walked back to his assigned dome. The afternoon clouds thickened and a light drizzle began to fall as the sun set; bad luck for observers. A bit after midnight we gave up and went to bed.

Friday, January 14, 2000 at 06:00:50 (EST) = Datetag20000114

TopicPersonalHistory - TopicProfiles

(correlates: PrimeFocus, DavidCopperfieldInFashion, SemiAstrophysicist, ...)