Monday, July 6, 2009

Yerkes Observatory Day Trip

Our friend Roger is visiting us from Vancouver - on his way, actually, to an antique telescope convention on the campus of Notre Dame later in the week. One of the side trips he wanted to take in the area was to Yerkes Observatory, one of the world's great observatories 100 years ago. Run by the University of Chicago on the shores of Lake Geneva, Wisconsin, it still holds the record for the largest refractor (lens-type) telescope - 40 inches (1 meter) in diameter.This telescope, and in fact, many of the premier telescopes of the 19th century were built by Alvin Clark and Sons, a source of research for Roger, so of particular interest. Refractors were soon superseded by much larger reflecting (mirror-type) telescopes and astronomers never looked back... Research is still ongoing, but mostly involving comparison observations taken decades ago with the same telescope. Of course, southern Wisconsin was never a great location for a large telescope, and there is considerable light pollution from metropolitan centers along the western shore of Lake Michigan.

So last Friday, the day before the 4th holiday, Roger arranged a tour of the facility and we did the 75 mile drive north, joined by Melinda's sister Susan as well. Our tour was given by Richard Dreiser, who has been there for 30 years. Melinda and I have been through the place before, but it is an interesting place and we learn something new every time. The tour starts on the outside of the building with the architecture and exquisite stonework before moving into some of the historic offices, library, and eventually, the cavernous dome of the great refractor.

The dome is huge! It almost seems larger from the inside that it appears from outside. Of course, the size of the dome is driven by the length of the telescope - one of the reasons the Mirror Lab where I work makes very short focal length telescopes - to ultimately lower the cost of the telescope enclosure. But partially because of the refractor optics, the color error they generally suffer from is minimized if the focal length is made longer, so refractors are generally long, this one being about 65 feet (20 meters) long. And as it moves around the sky, the instrument or eyepiece varies a huge amount in height, so the floor, a full 75 feet (22 meters) in diameter, moves vertically about 30 feet (9 meters). And as a precision device, it is built massively, capable of tracking a star without errors for hours. Some friends of mine have actually been part of a group to observe with the telescope, but that opportunity comes rarely, if at all.

The telescope was dedicated in October of 1897, after being on display at the World's Columbian Exhibition in Chicago in 1893. The included cartoon is on display in the hall of the Observatory, from the front page of The Daily Inter Ocean, a Chicago newspaper, on dedication day. It champions the use of industry and technology for research even while in Europe there was a buildup in the war machine.

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