> 0 < (D CL -n 0 (D W (D 0 0 00 0 0 > 6 0 4 00 00 L 44. 0 0 0 CA) Engineering Facts The Mayall 4-Meter Telescope The 4-meter* (158-inch) telescope weighs 375 tons, 250 of which are in moving parts. The moving portion of the telescope is supported on a .005-inch film of oil by 9 bearings and is so precisely balanced that it can be moved by a one-half horsepower motor., The telescope is mounted on a concrete pier, 92 feet in height and 37 feet in diameter. The pier is struc- turally isolated from the rest of the building so that when the wind shakes the building the telescope remains undis- turbed. The main observing area is maintained at a tem- perature equal to that of the nighttime air. This ensures that no turbulent air distur- bances will be created when the dome is opened and the telescope is to be used. The dome weighs 500 tons, rotates on 32 sets of wheels around its 105-foot diameter, and is designed to withstand gale force winds up to 120 mph. In addition to the telem scope and its operating facilities, the building houses a mirror aluminizing chamber, photographic dark- rooms, mechanical and elec- trical shops, offices, a kitchen and a dormitory. The heart of the telescope is its fused quartz primary mirror, 4 meters in diameter-or just over 13 feet. It is 61 cm. (2 feet) thick and weighs 13.6 metric tons (15 tons). Its surface was ground and polished at the KPNO optical shop in Tuc- son, in a painstaking process that took three years. Its re- flective coating-a uniform layer of aluminum 1/1000 the thickness of a human hair-is replaced approximately every two years. The secondary mirror, which is on the "flip side" of the prime-focus cage, is 1.3 meters (52 inches) in diameter. The telescope is operated from the console room. A computer controls the tele- scope's pointing and tracking, dome position, and most of the functions of the auxiliary equipment. The telescope and building cost approximately $10 mil- lion and have been in opera- tion since March 1973. The project was funded by the Nam tional Science Foundation. Kitt Peak National Observatory RO. Box 26732 Tucson, Arizona 85726 41 AURA.. Kitt Peak National Observatory 91, > 0 < (D CL -n 0 (D 2) CA (D *Only the dimensions of the tele- scope's mirrors are given in metric units- Astronomical Research How the Telescope Works Astronomers from throughout the United States and the world come to Kitt Peak to use the Mayall 4-meter (158-inc 'h) telescope. The telescope, named after Nicholas U. Mayall, Obser- vatory Director from 1960 to 1971, is funded solely for as- tronomical research. Visiting astronomers from other in- stitutions use over 60 percent of the research time, and sci- entific staff members at KPNO are scheduled for somewhat less than 40 per- cent of the nights. Some of the visiting observers are graduate students working on doctoral dissertations. To obtain telescope time, an astronomer submits a de- tailed scientific proposal to KPNO at least 6 months in advance. Competition for ob- serving time is very keen and the telescope is scheduled for astronomical research every night of the year except Christmas. It is also used fre- quently for daytime observa- tions at infrared wavelengths. As a result of this constant scientific use, time to look through the telescope cannot be extended to the general public. The 4-meter telescope is reserved for observations at extremely low light levels. Some of the objects observed, such as quasars and galaxy clusters, appear faint simply because they are so very dis- tant. Other objects are rela- tively nearby but intrinsically faint, such as the wisps of material in the remains of exploded stars. Projects scheduled on the 4-meter telescope cover a wide variety of astronomical subjects. Recent observations have included: 9 a search for planetary com- panions to stars other than the sun * studies of stars in the proc- ess of condensing out of gaseous clouds * searches for black holes 9 infrared observations of the nucleus of the Milky Way Galaxy * measurement of the internal motions and masses of galaxies * determination of the expan- sion rate and age of the universe The continuing use of the Mayall telescope makes sig- nificant contributions to U.S. and international astronomy. The Mayall telescope moves on two sets of main support bearings: the "horse- shoe " bearing for right as- cension (corresponding to longitude in the sky) and a perpendicular set of bearings for declination (correspond- ing to latitude in the sky) - The right ascension bearings are mounted parallel to the Earth's axis of rotation and the telescope can track an ob- ject westward across the sky by moving on these bearings at the rate necessary to com- pensate for the Earth's rota- tion. As the telescope moves, the dome of the building also rotates so that the telescope has a clear view of the sky through the opened slit. All of these motions are controlled automatically by a computer. While using the telescope, the astronomer can choose one of three focus positions: Primefocus (f/2.8), inside the large black cylinder near the top of the telescope. This focus is formed by only one mirror, the main 4-meter mir- ror. To use this focus, the as- tronomer actually rides inside the cylindrical cage. Prime focus is used mainly for direct photography, sometimes with electronic detectors instead of photographic plates. Ritchey-Chrgtienfocus (f/8), just beneath the main 4-meter (158-inch) mirror. This focus is formed by two mirrors: the 4-meter primary and the 1. 3 meter (52 inches) secondary. The secondary mirror is located in the same black cylinder that holds the prime-focus camera. To change from one focus to the other, the telescope operator simply flips the mounting ring that holds the central cylinder-an operation that takes only about 15 minutes. One of several instruments can be used at this focus: a spectrograph (which sepa- rates starlight into its compo- nent colors), a photometer (which measures light inten- sities), or a camera for direct photography. Coud~focus (f/ 160), in a stationary observing room ad- jacent to the telescope's base. This focus is formed by the primary mirror plus four smaller mirrors that direct the light beam to the observing station. Since the coud6 focus is in a fixed position, large and heavy instruments can be used. Key to front cover illustration (Fold front cover back for easy reference.) I .Building is 56.7 meters (186 feet) or approxi mately 18 stories high 2. Dome cranes-50-ton and 5-ton capacity 3. Prime focus cage 4. Ritchey-Chr&tien focus 5. Coud6 focus laboratory 6. Telescope control room 7. Visitors' gallery 8. Visitors'scenic walkway-26.8 meters (88 feet) above ground 9. Telescope pier 10. Second floor-dormitory 11. Ground floor -visitors' entrance at 2082 meters (6830 feet) above sea level Horsehead Nebuia in urion, N(JU ZU24. KFNU 4-meter pnotograpn.