Fun with a 6.5 meter telescope

by Mike J. Shade


I suppose that the old saying "the squeaky wheel gets the grease" held true in this case. Since I have become one of the most vocal opponents of light pollution in Santa Cruz County AZ, Whipple Observatory on Mount Hopkins, south of Tucson AZ decided that some sort of award was in order. They had a volunteer appreciation night and invited a guest and I to tag along. What we got was a tour of the facilities on the mountain and to watch as real astronomers got to do real astronomy. Oh, they provided a nice meal as well for us.

We arrived at the visitor center and were driven up the mountain to the observatory. Since we have had more than enough annoying weather lately, there was snow on the road and the streams were running. People who think of Arizona as nothing but cactus are mistaken. The Santa Rita Mountain range is considered one of the so called "sky islands" in that their weather and such is much different than most other (lower) places in Arizona. There were evergreen trees as we climbed out of the valley, and the temperature dropped considerably.

Reaching the top, we got to examine the 10-meter gamma ray telescope, something that resembled a radio telescope. Then it was off to the 60-inch telescope for a critical examination of this instrument and its neighbor, a little 48-inch scope. Both were packed with sensors, computers, wires, cables, and such and it was difficult to see the actual telescope.

Finally it was the grand finale of the trip-we got to go into the observatory that houses the 6.5 meter (~260-inch) reflector, currently the largest single mirror telescope in North America! We were able to examine it from the top level looking down and from the floor, right next to it! It is a massive instrument, a large mirror tub containing the primary with a massive inverted Serrier Truss system. The "truss rods" were something on the order of three feet in diameter! On the back of the primary mirror were the sensors and actuators to help keep the mirror in its true shape. The sensors examine temperature and final wavefront of the mirror and the actuators move slightly to keep the mirror in its true shape. The mirror is hollow and there are plans to add a cooling system-cold air blown through PVC pipes in the mirror-in the near future. For our benefit, the mirror cover was taken off and we could actually look at the primary. What a massive piece of glass! Since this is an active telescope, they just had to open the shutters at the back of the building and then open the observing slit. What a view of Southern Arizona! And of course they had to position the building properly so the whole building was rotated while we got to ride the dome and see a panoramic view from 8500' up. Remember that this is an alt-az type of instrument so the telescope itself moves in altitude and the whole building rotates in azimuth so they actually moved the whole building.

After a nice dinner, a few hardy souls got to go up to the 60" control room while this instrument was being used. They were looking for planets around other stars so were looking at the spectra of target stars. We got to see the actual raw data and the instrument slew to another target (that should make any LX200 owner grin although it was about 1/4 as loud!). We also got to see some of the instruments attached to the telescope, including some really big CCD arrays. We finally left the mountain about 11 or so, very impressed.