TEL19 Mayall 4meter telescope

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The Mayall 4-meter telescope, which dominates Kitt Peak's skyline, was completed in 1973 at a cost of $10 million. The huge building, which is almost 200 feet high and contains 30000 square feet of office and laboratory space, can be seen from over 50 miles away (both authors have seen it from Texas Canyon, east of Tucson on I-10, and it is easily visible from Tucson International Airport). At sunrise, the shadow of the dome races across the

The Mayall 4-meter telescope from the access road leading up to it. Image courtesy of National Optical Astronomy

Observatory/Association of Universities for Research in Astronomy/National Science Foundation.

desert floor, almost 4000 feet below the summit. There is a public viewing gallery high in the building, giving a 360-degree view of the surrounding desert.

The main mirror is 158 inches in diameter, and weighs 15 tons. It is fixed to an equatorial mount, and the telescope structure is 92 feet long. In order to separate the telescope from vibrations in the building - particularly when the dome is moving - the mount is attached to a concrete pier that is completely separate from the building. There is a surprising amount of space on the mount floor surrounding the telescope - this is necessary in order for the telescope structure to be able to move through all angles without hitting anything inside the dome. (Visitor Center tours will take you to the visitors' gallery on the mount floor.) The dome around

the telescope has a moving weight of 500 tons, and it was designed to withstand winds of up to 120 miles per hour.

ROLL-BACK PROTECTIVE SHUTTER ALLOWS STARLIGHT TO REACH TELESCOPE

TELESCOPE MOUNTED ON BEARINGS WHICH ALLOW IT TO POINT AT ANY PORTION OF THE SKY

PRIME FOCUS CAGE (F/2.7 PRIME FOCUS)

VISITORS TELESCOPE VIEWING GALLERY

VISITORS SCENIC ^ C VIEWING GALLERY

RITCHEY CHRETIEN CAGE (F/8.0 CASSEGRAIN FOCUS)

TRUCK LOADING AREA

TELESCOPE MOUNTED ON BEARINGS WHICH ALLOW IT TO POINT AT ANY PORTION OF THE SKY

PRIME FOCUS CAGE (F/2.7 PRIME FOCUS)

VISITORS TELESCOPE VIEWING GALLERY

VISITORS SCENIC ^ C VIEWING GALLERY

RITCHEY CHRETIEN CAGE (F/8.0 CASSEGRAIN FOCUS)

TRUCK LOADING AREA

CONCRETE FOUNDATION SUPPORTS TELESCOPE STRUCTURE INDEPENDENT OF BUILDING

DORM AREA MACHINE SHOP

LOUNGE

HEMISPHERICAL ROTATING DOME ALLOWS OBSERVATION OF ANY PORTION OF THE SKY

TELESCOPE COMPUTER CONTROL ROOM

(COUDE ROOM OBSERVING AREA) F/160 COUDE FOCUS AUXILIARY

INSTRUMENT ROOMS ON THIS FLOOR ELECTRONICS LAB

CONCRETE FOUNDATION SUPPORTS TELESCOPE STRUCTURE INDEPENDENT OF BUILDING

DORM AREA MACHINE SHOP

A sketch of the 4-meter telescope. Note that the concrete pier on which the telescope mount sits is not connected to the rest of the building. This is to isolate the telescope from any building vibrations, which would cause blurred photographs. Image courtesy of National Optical Astronomy Observatory/ Association of Universities for Research in Astronomy/National Science Foundation.

LOUNGE

If you go on a tour of the 4-meter telescope, you will find the dome area to be cold on even the hottest day. The dome is refrigerated during the day to the expected night-time temperature, in order to avoid heat ripples coming off the floor. In addition, there are huge vents around the dome (they were installed in 1997), through which air is circulated at night.

Inside the 4-meter telescope dome. The primary mirror sits in the structure inside the blue yoke of the equatorial mount, but is covered during the day to protect it from dust and debris. The polar axis of an equatorial mount points directly at the celestial pole. A motor on that axis makes the telescope rotate exactly opposite to the Earth's rotation, so that stars will stay fixed when an image is taken, while the telescope stays fixed on the declination axis. The huge equatorial mount of the Mayall 4-meter telescope weighs over 50 tons. Photo courtesy of National Optical Astronomy Observatory/Association of Universities for Research in Astronomy/National Science Foundation.

The 4-meter telescope spends much of its time looking at other galaxies; how they are distributed in the Universe, changed with time, and what makes them the way they are. In particular, the 4-meter telescope has been used to investigate new ways of estimating distances to galaxies. It seems that instead of being distributed randomly through the Universe, galaxies lie together along long filaments or sheets. The seeds of this structure were probably laid in the earliest phases of the Big Bang, when the Universe was created, so in principle determining the distribution of galaxies allows astronomers a glimpse at the structure of the Universe when it was very young (14 billion years ago).

One of the biggest problems in astronomy is determining how far away objects are. To a certain extent, we are familiar with this in everyday life. For example, a faint light could be a flashlight in the dark a few hundred yards away, a car's headlights half a mile away, or an aircraft's landing light 20 miles away. Astronomers have devised techniques for estimating the intrinsic brightness of distant galaxies, based on observations of stars or nebulae within them. When the distance is combined with a measure of the red-shift velocity, they can determine the Hubble constant, the rate at which the Universe is expanding.

When stars explode as supernovae, they can - for a time - outshine the light of the rest of the galaxy, so they are visible to very large distances. An ongoing project at the 4-meter telescope is observing supernovae in very distant galaxies. One particular class of supernova turns out to be a good distance indicator, thereby allowing researchers to probe how fast the Universe was expanding when it was much younger. Armed with this information, they can investigate how much mass is in the Universe, and determine the size of the cosmological constant that has accelerated the Universe's expansion during the last half of its existence.

The 4-meter telescope also is used to study relatively faint or distant stars in our Galaxy, including searching for brown dwarfs (which are "failed" stars), and for MACHOs, the MAssive Compact Halo Objects, which might make up a considerable amount of the mass of our Galaxy. This is a continuation of the huge role the 4-meter telescope played during the 1970s and 1980s in establishing that most galaxies have large amounts of dark matter associated with them. Many astronomers did not really believe the early claims that the outer regions of nearby galaxies were rotating faster than they should be if we could see all the mass, but establishing that this was so was important enough that KPNO devoted a lot of telescope time to settling the controversy. Recently, the 4-m telescope has been used a lot for near-infrared observations.

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