Observatory 5: Yerkes, Part 2 – The Night Program Experience

Written at Sturtevant, WI, Amtrak Depot on Tuesday, August 14

Yerkes observing last night was awesome and strangely mediocre. It was amazing to use that venerable, world’s largest refractor and to see how it would have been used for science (more or less). The scope itself weighs 6 tons! And one guy can move it around with surprisingly little effort It’s that well balanced. Like at Allegheny (or probably the other way around), the floor is a giant elevator with the pier in the center isolated from it and the rest of the building. So we moved up and down all night. The floor weighs something like 36,000 lbs with 48,000 lbs. of cement counterweights around the perimeter. A small DC motor moved it up and down — the ORIGINAL 1897 motor! Similarly the original motor runs the clock drive (I think I have that right).

Dan Koehler (KAY’ lur), the director of public relations and tours with whom I corresponded, led the program, as he has done for some 27 years. He is extremely knowledgeable and talked almost the whole time. (We started at 9:00p and ended about 11:45p.) With 18 people in the group we didn’t have huge blocks of time to stare but we weren’t really rushed either. You could look 2 or even 3 times at each object. We saw six objects: Jupiter, Saturn, M11, M17, M27, and M2. These were chosen for their various classes – planet, open cluster, reflection nebula, planetary nebula, and globular cluster – and their positioning. Dan gave detailed descriptions of each, specifically and by class.

The scope is 40” in diameter (the lens is, any way) and 63 feet long with a focal length of 19,100± cm. So the focal ratio is f/19, which means the field of view is tiny! I don’t remember the formula, but it’s really small. Good for planets, not so good for deep sky nebulae. We used a 40mm Explore Scientific (I think?) eyepiece, and that gave us magnification of 475X. It was a great big eyepiece – like a coffee mug or soda can – good for public viewing. Dan’s assistant (read: guy that does all the work) was named Chuck, I think. Let’s call him Chuck. Chuck would slew the six-ton scope around by hand to get it in roughly the right place, then check the giant setting circles (big wheels on each axis of the mount with coordinate system numbers), then adjust again to get about where the object should be by coordinates, then adjust the dome (and the floor as needed) to line up with the scope, then use the 6” finder scope, then jigger the thing to get the object centered in the eyepiece. It took up to 10 minutes for some objects. Dan advised and helped as needed and gave commentary. Then we would get to line up or blob up and take turns looking. We started with lights on, then level by level they were turned off.

Dan talked a little about the fate of Yerkes. He doesn’t know much for sure, but there is a group of concerned, local supporters that have been negotiating with UChicago. It sounds hopeful, but the lack of clarity and information is obviously frustrating to Dan and the others who are waiting to see if they will have jobs. Also, Dan reminds me a lot of Thom Lamb in appearance and manner.

After we observed the six objects, they brought the lights up and a bunch of us took pics with the scope. I got someone to take a couple of me, one looking at the camera and one looking into the eyepiece. The second is a pretty stupid picture, of course, because (1) the lights were on (2) the dome was closed (3) the scope was no longer even pointed at the shutters, all of which is plainly apparent. Oh well. The first one is a good picture. The evening ended pretty unceremoniously. I don’t remember if anyone even said, “Good night, thanks for coming.” It was just okay, that’s it, here’s the stair down to the door. Scientists are not always sentimental.

I stood outside for a little bit, letting my eyes readjust to the dark to see what the sky looked like. Pretty much like ours at home, I guess. I hoped to see a meteor before going, as the Perseid meteor shower had peaked just the night before, and eventually I pretended I did. It was midnight and I had an hour to drive after a long day, so I hit the road.

Details about the observations are coming up next.

Again, >click here to see my pictures from Yerkes<