Yesterday's Tommorrow Today

Here's a slew of old science and technology articles from the Modern
Mechanix magazine, among which we have the following.

http://blog.modernmechanix.com/2008/08/01/the-worlds-biggest-eye/

*****
Modern Mechanix
June, 1934
The WORLD?S BIGGEST EYE

A GROUP of American astronomers soon will experience one of the
greatest scientific thrills of the century. On the night the world?s
most tremendous telescope is completed they will take turns peering
into a tiny, brilliant eyepiece.

Looking at the heavens with the aid of the most extraordinary piece of
glass ever poured, they may make discoveries that will completely
change man?s conception of the universe.

After years of research the men in charge of building the monster
instrument for the California Institute of Technology are now at work.
Astronomers estimate that the mirror, 360,000 times more powerful than
the human eye, will magnify the moon and planets 10,000 times. Through
the telescope the moon will appear only twenty-five miles away, at
which distance large buildings could be easily seen. The 100-inch
telescope on Mount Wilson, only half the diameter of the newest
instrument, can detect a candle flame 5,000 miles away. With the aid
of this telescope approximately 2,000,000 nebulae, each as crowded as
the Milky Way, have been found. It can peer into space a distance of
400,000,000 light years.

The new telescope, astronomers hope, will penetrate at least three
times farther into space, thus opening an unexplored sphere thirty
times the size of that now sounded. Already tasks that appeared
insurmountable have been overcome in constructing the curved mirror
that has 240 square feet of surface and is to be smoothed to an
accuracy of two one-millionths of an inch.

Under the guidance of Dr. George Ellery Hale, who built the 100-inch
telescope, leaders in many branches of science are co-operating with
the International Education Board of New York which provided the
$6,000,-000 telescope fund. Drs. J. A. Anderson and Francis G. Pease
of the Mount Wilson observatory are in charge of the work.

Instead of gathering light by lenses, all large astronomical
telescopes use a curved mirror to gather the light from a star and
focus it at one point inside the barrel of the telescope. There a
prism diverts the light to a point outside the barrel, or a flat
mirror returns the gathered light will be able to sit inside the tube,
directly in the path of the incoming light, for in spite of the shadow
the observer will cast on the mirror, less light will be lost than if
the rays were shunted outside.

The most crucial part of the project?that of making the giant
reflector?is now well under way. The problem was to find a material
that could be ground to the necessary accuracy and that would remain
unaffected by atmospheric changes. Glass and fused quartz were tried
but a super pyrex borosilicate glass finally was selected after a
trial mirror 120 inches in diameter, the largest ever made, was
poured, allowed to cool and examined. The giant 200-inch disk of this
substance was poured recently. Instead of a deep disk, the mirror is
comparatively thin, with an intricate system of ribs and webs on the
back to give the surface strength and to provide grips for the metal
backing. Even in this thin form, the completed mirror will weigh
nearly twenty tons. Months will be required for the mirror to cool,
after which it will be ground and polished. In the final stages
polishers will work less than an hour a day. Otherwise the heat from
their bodies might affect the curve on the surface.

Instead of silver, the new mirror will be coated with aluminum. Inside
a huge vacuum chamber individual atoms of aluminum will be deposited
on the glass surface, giving it a reflective power greater than that
of silver and one that is especially sensitive to weak ultraviolet
rays. Meanwhile, a vast amount of auxiliary instruments like
thermocouples, spectroscopes, and photoelectric cells are being built.
Among other unique devices is a solar furnace consisting of mirrors
and burning glasses with which astronomers hope to focus the sun?s
rays and obtain a heat approximating the 6,000 degrees centigrade
temperature of the sun?s surface.

The ponderous fork-type mounting from which the telescope barrel will
swing is also being designed. Huge motors and cylinders of compressed
air will move the whole base under the control of an astronomical
clock so that after the instrument has been pointed at a star, it will
automatically follow the object as the earth turns. A change in
temperature of only a few degrees would influence the ?figure? of the
mirror, throwing its focal point out, so the huge dome is to be
double-walled to prevent the entrance of heat during the daytime. The
mirror will remain covered and protected when not in use, and water
circulating around its mounting will keep the mass at the same
temperature as the outside air when the shutters of the dome are
rolled back. The mirror will never be used to observe the sun, for the
hot rays might permanently disfigure its surface.

Contrary to accepted notions, the telescope will rarely be used for
visual observations of the stars. Photographic plates are infinitely
more sensitive to light than the human eye. By means of time exposures
astronomers can obtain pictures of stars so faint the eye would never
detect them. In the future astronomers will make their greatest
discoveries in the photographic dark room.

Instead of trying to make the telescope increase the size of star
images, astronomers hope that it will condense them to the tiniest
pin-points of light. No telescope powerful enough to show the shape of
a star can be built and the goal of the telescope builders is to
achieve an instrument in which even microscopic vibration is absent.

Nearly as important as the mirror itself is the site at which the
telescope is to be erected. A place where the stars twinkle less is
sought. Twinkling is caused by unequal densities in the air, giving a
fuzzy appearance to star photographs. The choice now has narrowed down
to one of four mountain tops.

Related posts

* 200 INCH TELESCOPE Is Greatest Engine of Science (Jun, 1934)
* Photographing Stars with a Rocket (Jun, 1934)
* THE POOR MAN?S TELESCOPE (Jun, 1934)
* How They Trailed a New Planet (Jun, 1934)
* 2,000-Inch TELESCOPE May Reveal End of Universe (Jun, 1934)
* Rocket?s Flight Kept In Sight (Jun, 1934)

*****
--
Dave
.

Relevant Pages

  • Re: Yesterdays Tommorrow Today
    ... most tremendous telescope is completed they will take turns peering ... Astronomers estimate that the mirror, 360,000 times more powerful than ... clock so that after the instrument has been pointed at a star, ...
    (sci.astro.amateur)
  • Re: adaptive optics without adptive optics?
    ... > astronomical telescope with large opening is mainly caused by ... > crucial component is an adaptive mirror made of elastic materials. ... > be a star neighboring the object of interest. ... It would be very difficult to establish whether some fuzzy feature ...
    (comp.dsp)
  • Re: Newtonian holiness
    ... Newtonian telescope? ... Consider a star anywhere in the field of view. ... from that one star shines on the entire surface of the mirror, ... no different in principle than a shadowed segment. ...
    (sci.astro.amateur)
  • Re: Newtonian holiness
    ... Newtonian telescope? ... The central obstruction is before the light is focussed by the ... Consider a star anywhere in the field of view. ... from that one star shines on the entire surface of the mirror, ...
    (sci.astro.amateur)
  • Planet finders use much faster instrument to discover distant planet (Forwarded)
    ... -- Astronomers have discovered a planet orbiting a very young star nearly 100 light years away using a relatively small, publicly accessible telescope turbocharged with a new planet-finding instrument. ... The feat suggests that astronomers have found a way to dramatically accelerate the pace of the hunt for planets outside our solar system. ... Their work is important in part because of what the astronomers found -- a planet, at least half as massive as Jupiter, orbiting a star just 600 million years old. ...
    (sci.astro)
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