Commentary

Observing with the Great Refractor

Once upon a time, Harvard College Observatory was actually an observatory. Today it is an office building spilling down the side of a hill at the edge of Cambridge, Massachusetts, and the best thing to observer from it are the fireworks over the Charles River on the Fourth of July. But in the middle of the 19th century, it was a working, state-of-the-art observatory that made ground-breaking studies of the sky.

Harvard's “Great Refractor” is a 15 inch diameter telescope perched upon a 33 foot granite tower. For the 20 years following its installation in 1847, it was the largest telescope in the United States, and was among the largest in the world. With it, the eighth moon of Saturn and Saturn's inner ring were discovered.

The telescope originally had a wooden tube veneered in mahogany. This tube was evidently damaged, and the upper portion was replaced with a metal tube. Despite this, enough of the original tube remains to give an elegance to the telescope. Because the telescope is mounted eleven feet above the floor of the observing room, an observer must sit high upon a two-seat bench mounted to a curved wooden scaffold to look through the eyepiece. The scaffold runs on a track around the telescope. An observer raises and lowers the bench on the scaffold with a hand-crank.

The telescope had long fallen into disuse by the time I became a Harvard graduate student in 1979. The only time anyone came to the telescope was during public observing nights, when visitors would be lead through the telescope's dome. But the telescope was displayed rather than used; observing was done with small portable telescopes set up by graduate students on the rooftop of the modern section of the observatory.

After one open house, when the visitors had left and we had put the portable telescopes away, I was passing the time with two other graduate students, Carol and Jurgen, in the dome of the Great Refractor. I had been at Harvard for several years by this time, and I had worked many of the open nights, but I had never seen the Great Refractor used or the dome opened. “Why wasn't it used?” I asked. Jurgen said he had been told that “the dome can't open.” “Really? What's wrong with it?”

For a natural sceptic, this was a dangerous line of thought, because it impelled me to look at the shutter mechanism. Cables from the top of the shutter ran to the side opposite of the shutter, where they attached to a large drum with a cog and a small latch. It look okay to me, although there was no crank attached to the drum. So impulsively I flipped the latch up, not expecting much to happen.

The drum immediately began whirling like a saw blade, and I watched the shutter slide in free-fall to the bottom of the dome, stopping with a loud crash at the bottom of its track. Jurgen turned to me and in a panicked voice asked “what did you do?” I didn't answer: I was preoccupied with counting my fingers to be sure they were all there and wondering whether a part of the shutter had fallen to the sidewalk below. Observatories are dangerous machines, and several astronomers have been injured or killed by them; I was hoping this was not one of those occasions.

Looking at the shutter, I could now see the problem: it wasn't that the shutter could not open; rather, the shutter would not easily close, because the counterweights to the shutter were detached. Worst yet, there was no sign of a handle for cranking the shutter closed. So Carol when off to find the person with the handle, and I stayed behind with Jurgen to watch the telescope.

Once we were alone, Jurgen calmly said “well, let's look at something,” as if nothing unusual had happened. I was feeling sheepish, feeling that I had done too much already, but Jurgen wanted to use the telescope, so he went over to an ancient control panel that looked to be half a century old and turned it on. “Perhaps we can turn the dome,” he said, and he hit a button. The dome moved. “What should we look at?” he asked. We ruled out the Moon as being too cliche, although I later learned that this was the first object observed with the Great Refractor. After some discussion, we settled on Saturn, and we set the dome's slit on the planet. We pulled the observing scaffold around, and we cranked the observing bench to a level that placed the telescope in line with Saturn.

I really expected more than what I saw. The dome was hot, so the warm air rising out of the slit made Saturn dance in the telescope. But the image was bright, and just the idea of using such a classic instrument was thrilling and memorable.

Eventually Carol showed up again, having found the crank. Of course, she also looked through the telescope. And then, with much exertion, we cranked the shutter closed.

But this little accident didn't go unnoticed, and several days later, as I walked to my office to work the night away on the computer, I notice that the telescope dome was again open. Fearing something bad had happened again, I walked up into the dome to find two of the Sky and Telescope guys using the telescope. Word had traveled that the telescope was useable (Sky and Telescope's offices are a couple of miles west of Harvard College Observatory). The Sky and Telescope guys, of course, had the good sense to open the balcony window of the dome, which helped cool the dome and steady the image. They invited me up, and I spent part of another evening observing with the Great Refractor.

From that time on while I was at Harvard, we opened the dome and let visitor observe with the Great Refractor during the public open nights. I see from the Harvard web site that they are now restoring the telescope. I hope this telescope continues to have an active life, and has not simply become a museum piece. What better life can this instrument have than to show the public what astronomy was like in the 19th century?