CIA-RDP96-00788R001400020003-3

The Mayall 4-Meter Telescope
Engineering Facts
Approved For Release 2000/08/07 : CIA-RDP96-00788R001400020003-3
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 8
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 tele-
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 Na-
tional Science Foundation.
*Only the dimensions of the tele-
scope's mirrors are given in metric
units.
Kitt Peak
National Observatory
P.O. Box 26732
Tucson, Arizona 85726
Kitt Peak National Observatory
12
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Approved For Release 2000 06/07 - CIAR
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AURA

Approved For Release 2000/08/07 : CIA-RDP96-00788R001400020003-3
Astronomical Research
Astronomers from
throughout the United States
and the world come to Kitt
Peak to use the Mayall
4-meter (158-inch) 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:
· 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
. 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.
Horsehead Nebula in Orion, NGC 2024. KPNO 4-meter photograph.
How the Telescope Works
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:
Prime focus (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-Chrétien focus
(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.
Coudé 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 coudé focus
is in a fixed position, large
and heavy instruments can
be used.
ed
The Mayall 4-meter telescope control room
Key to front cover illustration
(Fold front cover back for easy reference.)
1. 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-Chrétien focus
5. Coudé 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
se 2000/08/07 : CIA-RDP96-00788R001400020003-3