In August of 2011 we were traveling through Wisconsin and couldn't pass up the chance for a visit to the Yerkes Observatory in Williams Bay. It is the home of the world's largest refractor and the objective lens is 40" in diameter. This lens is a rather remarkable achievement since a telescope objective should be optically correct to about 1/4 of a wavelength of light. Making a lens this large and this accurate was a pretty tough task. Here's a little background on how the observatory came to be and what it is today.

The observatory is named after Charles Tyson Yerkes who was a somewhat shady entrepreneur in the 19th century. He had a rather checkered path. He cheated investors and misused their money while getting very rich himself. When he was in Chicago he created an empire of streetcars and, when things got too hot in the United States, he went to England. There he purchased a number of disparate underground subway lines and merged them into a unified company. The current London Underground system owes much to him.

At the end of the 19th century there was a push in the United States to be the biggest and best in any field. Astronomy was no different and there was a rush to make the biggest telescope in the world. The Yerkes Observatory is the result of this ambition and the happy meeting of science and money.

In 1892 George Ellery Hale, a young astronomer, had the ambition to build a large telescope and was aware of large lens blanks that would be perfect for a 40" objective lens. The cost to figure these blanks, build a suitable mounting, acquire a site, erect observatory buildings, and operate the telescope was daunting. Enter Charles Tyson Yerkes.

Yerkes wanted to be part of this endeavor, not so much for science but for self promotion. He envisioned the world's largest telescope being housed in a pyramid structure in downtown Chicago as a monument to himself. Eventually sanity prevailed and the site was changed to Williams Bay, Wisconsin. While not an optimal site for good seeing it was better than downtown Chicago. Hale would have preferred a remote, dry, desert mountain for optimal seeing but Williams Bay was better than downtown Chicago. For Yerkes, Williams Bay was the summer home for many of the rich and famous of Chicago so "his" telescope would be visible to his friends.

Warner and Swasey were tasked with building the mount and Alvan Clark was to create the objective. After some setbacks (including the collapse of the raised floor of the telescope dome just prior to opening) the telescope became operational in 1897. Hale was the Observatory's first director.

Visiting today you're impressed with the opulence of the observatory. This was more than just a functional home for a scientific instrument but was also a rather luxurious building designed to impress visitors. Even the grounds were designed by landscape architect Frederick Law Olmsted. You find marble everywhere and ornate carvings on the buildings. It's a great example of elegant 19th century institutional architecture. The telescope itself is impressive: the tube is 64' long and the pier is 65' high. The floor is an elevator 75' across. It's very disorienting when the floor is raised or lowered while you're standing on it. The floor has about 23' vertical travel.

People take pictures of the telescope more than pictures of the surroundings. Most of the images I took are not of the telescope but of the rather unique building exteriors and interiors. Today you don't find observatories with this level of architectural imagination and detail.

Here's the main entrance.
Note the "Y" for "Yerkes"
	There are two smaller domes attached to the main structure. They house a 40" and a 24" reflector. We didn't see these instruments when we were there.
The dome for the 40" telescope.	I think they use this little dome for star parties for the public. It struck me as a nicely scaled dome for a backyard observatory.
I'm not sure who these people were but I suspect that they were famous astronomers or people associated with the Observatory's founding.
Let's go inside now.
Some of the early instrumentation.
The astronomers' library. Note the step stool for getting to the higher shelves.	The entrance hall looks like it belongs more in Yerkes' mansion than in an observatory.
	These are the staff mailboxes. Note the light at the top.
These are the steps up to the big refractor floor.
And now up those steps to the 40" refractor....
It's really hard to get the whole 64' of telescope tube into one shot with the lens that I was using.
Those are really big setting circles. I don't know how you'd use them because they're so far from the floor.
Say, who is that up in the top of the dome?

The University of Chicago was the ordinal operator of the observatory but in 2020 ownership was transferred to a private nonprofit. Prior to this transfer the University had gradually scaled back access to the point where there were no tours or observing nights. There were also significant maintenance problems. These days extensive renovations have taken place and a lot of deferred maintenance has been completed. The roofs don't leak anymore. It's a much friendlier place for astronomy tourists. You can even hold your wedding there.

Here is some information on the history of the telescope and the creation of the observatory.

The Yerkes home page has less detail but does have information about tours and events.

Read about Alvan Clark who made the objective lens and Warner and Swasey who built the mounting.