Professor Kyle Cudworth uses the 40-inch refractor nearly every night that weather permits to study the motions of stars. Planets move relatively quickly across the sky (hence their name, Greek for "wanderers"). Stars move too, only they are so much farther away than the planets that they appear to move very slowly, so slowly that even over a year, the motion is generally barely detectable for even the fastest moving stars. So, in order to study how stars move, you need lots of pictures carefully taken with the same instrument over many years. Ritchey and Barnard took photographs with the 40-inch refractor before 1910, and, by combining these photos with the ones Dr. Cudworth takes today, he can get significantly higher precision than anyone else gets anywhere else in the world.
The other large telescope at Yerkes, the 40-inch reflector (usually called the 41-inch to avoid confusion with the other 40-inch), is currently being used to test an adaptive optics system, called the Wavefront Control Experiment (WCE). Adaptive optics is a relatively new way of "taking out" atmospheric distortions. The atmosphere adds distortions to starlight -- it's what makes stars twinkle, and also what makes the road shimmer on a hot day. To avoid these distortions, you can either lift a telescope above the atmosphere altogether -- put it in space -- or you can make a sophisticated, bendable mirror that bends in such a way as to "undo" the distortions added by the atmosphere. This is an adaptive mirror, hence "adaptive optics." For more information, see Sky and Telescope, both the May and June 1994 issues. For more information, see the summary written by Walter Wild, or the University of Chicago Adaptive Optics group page. See also ADONIS group from France at La Silla, and Atmospheric Compensation Experiment at Mt Wilson.
Here is some of the impressive equipment associated with the WCE
adaptive optics system. It's in the basement below the telescope. As
you can see, it's rather bulky, and this is only part of the system.
Since you don't want to have this actually attached to the telescope
(because it is sensitive and it might bend as you point the
telescope in all directions), all of the light from the telescope is
directed by a mirror down through a hole in the center of the telescope
mount. Thus, no matter where the telescope is pointing, all the light
collected goes to the basement where all the equipment is. A
telescope with this sort of arrangement is called a Coude
telescope, and the tube down which the light is redirected is
called the Coude feed.
Here, Rich points out the Coude feed for the 41-inch. Coude feeds are actually quite common; you need one if your instrument is too big or too heavy (or too delicate) to actually attach to the back of the telescope. This particular one is evacuated (meaning there is no air in the tube) so that there are no density variations along the light path to further distort the light.
When the webmaster first came to graduate school at the UofC, she was surprised that there were chalk boards everywhere, even in the hallways. This is because, she soon learned, that whenever scientists meet, even in the hallways, the conversation turns to science, and they generally have to write things down to communicate effectively. So, no flat space is sacred. The walls of the WCE room are all write-on/wipe-off boards.
This is the camera part of a device called an echelle (pronounced "es-SHELL") spectrograph that was partially developed at Yerkes and was installed in November 1998 at the 3.5 meter telescope at Apache Point Observatory. (APO is another observatory in which the UofC is a partner.) An echelle works like a prism that disperses, or breaks up, light into a spectrum. If you do this to light coming from celestial objects, you can learn what the object is made of and sometimes what the light went through on its way to your detector.
Here, Connie Rockosi shows us another view of the echelle spectrograph camera. Connie is a graduate student at the UofC; her PhD thesis will probably involve this instrument.
All of the instruments above work with visible light, but some of the other astrophysics done at Yerkes involves infrared (IR) light, which is light of longer wavelength than visible light. We sense some IR radiation as heat. In order for a detector to efficiently sense heat, it has to be colder than what it's looking at. The following instruments use supercooled liquids, usually liquid nitrogen and liquid helium, to get really cold -- minus 200 degrees Celsius would be a hot day!
Here Bob Hirsch poses with the 60-channel far-infrared photometer, a camera which flew on the Kuiper Airborne Observatory (KAO). The small silver cylinder on the side is a reservoir for helium-3, a light isotope of helium, which is used with liquid nitrogen and liquid helium-4 to cool the detectors to 0.2 Kelvin. (-272.8 degrees Celsius!) The main silver cylinder is the outer surface of the "thermos bottle" used to keep the liquids from boiling away. The thing that is hanging "through" the table on the bottom, called the "snout", holds some plastic lenses (opaque to visible light!), which are also cooled (if only to 4K!).
Here Rich Dreiser tempts fate with a hammer while Tom McMahon poses with STOKES, another infrared detector that flew on the Kuiper Airborne Observatory (KAO). This instrument is similar in construction to the 60-channel above. Here the "snout" and the "thermos bottle" have been removed and you can see the detector arrays. Unlike the 60-channel, though, this instrument isn't a camera; instead, it records the polarization of the infrared radiation it senses.
More views of the stuff in one of the labs. An IR detector (under construction) called HERTZ is in the foreground, and in the background is a device for testing the instruments called the "focused beam source" -- a telescope in reverse!
This is the last formal page on the tour! Head back to the main tour home page.
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