Optics and Telescopes
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Optics and Telescopes
Telescopes have been developed for every
portion of the Electro-Magnetic Spectrum
Optical
Radio
Infrared
Ultraviolet
X-Ray
Gamma Ray
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Optics and Telescopes
Telescopes on Mauna Kea
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Early Optical Telescopes use the Refraction property
of waves to collect and focus light
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A Refractor or Refracting Telescope
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One of several difficulties with a lens is that it
is a prism and colors bend at different rates.
Another is that it is extremely difficult to
obtain a large piece of glass that is of
telescope quality.
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Modern telescopes use the Reflective property
of waves to gather and focus light. By correctly
curving the mirror into a parabaloid shape light
can be collected and focused.
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There are several basic mounts for Reflector
telescopes that have been invented. Some of
them are shown below.
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Film has been replaced. Now data is digitized directly
using a CCD (Charge Coupled Device). These, too,
are becoming more and more sophisticated.
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Larger telescopes are
desirable to attain better
resolution. The image (a)
was obtained with a
telescope twice the size of
the telescope that took
image (b)
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Atmospheric blurring is
often due to air
movements. In the past
this has limited the size
of Earth based
telescopes. Solutions
have included
telescopes on mountain
tops and active optics.
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The best solution to date has been Adaptive
Optics that track atmospheric changes with a
laser then adjust the shape of the mirror in real
time to compensate.
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The Earth’s Atmosphere effectively blocks most radiation
from space. There is a window for visible light and a
rather large window in the radio wavelengths that can be
accessed from the ground. There are few infrared
wavelengths that can be accessed from high mountains
and high flying airplanes. The rest of the wavelengths can
only be seen in space.
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Much information can be obtained from Earth
based Radio Telescopes using the radio window.
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Radio telescopes are similar to optical reflecting
telescopes but are less sensitive to imperfections
in the receiver (due to the longer wavelengths)
and they can be made very large
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This is called the Very Large Array. It samples very
long radio waves. This large array has the resolution
of a telescope as large as the longest distance
between dishes. Signals are welded together by
interferometry as if they were coming from a single
instrument.
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Before adaptive optics and
before the advent of the large
land based optical telescopes,
the Hubble Space Telescope
was launched into orbit. It
amazed the community. It is
still doing an excellent job even
as old as it is. The new scopes
now are passing it by and they
need much less expensive
maintenance.
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Infrared
Ultraviolet
X-Ray
These are a few of the fleet of
telescopes that now cover the
wavelengths that can not be
seen from the surface of the
Earth.
Gamma Raytwlee2016@gmail.c
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Much can be learned from observing the
same astronomical object at many
wavelengths. Here is the Milky Way in
several wavelengths.
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End of Chapter 5
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