Lecture 4 — Techniques of Astronomy (white background) -...

PHYS 1160
Introductory Astronomy
and the Search for Life
Elsewhere
Lecture 4
Techniques of
Astronomy
This Lecture
• Telescopes
• Instruments for optical astronomy
• Radio Astronomy
• Observations from Space
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Telescopes
• Telescopes have been the key
tool for astronomical research
since their use by Galileo in
1609.
• Galileo’s telescopes and many
other early telescopes were
refracting telescopes.
• Today most telescopes for
professional astronomy are
reflecting telescopes.
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Refracting telescope
• A refracting telescope
collects light with a
transparent lens.
• The picture shows the 1m
refractor at the Yerkes
observatory in Chicago.
• 1 metre is about the largest
feasible size for a lens so
this design cannot be used
for very large telescopes.
– The lens becomes so heavy it
will deform under its own
weight.

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Reflecting Telescopes
• Reflecting telescopes use
a curved mirror instead of
a lens to focus light.
• The picture shows the 8m
Gemini North Telescope
at Mauna Kea, Hawaii.
• This type of design is
used for most modern
astronomical telescopes.
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Key features of a Telescope
• Light collecting power
– This is determined by the aperture of the
telescope - i.e. the diameter of its mirror or
lens.
– A bigger telescope collects more light and can
therefore see fainter stars or galaxies.
• Resolving Power
– Or angular resolution is the telescope’s ability
to see fine detail.
– This also depends on the telescope’s aperture.
• For these reasons bigger is always better
when it comes to telescopes.

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Mount Wilson
100-inch
The 100 inch (2.5m) telescope
The 100 inch (2.5m) telescope
at Mount Wilson observatory
at Mount Wilson observatory
(near Los Angeles) was
(near Los Angeles) was
completed in 1917.
completed in 1917.
It made important discoveries
It made important discoveries
– including Edwin Hubble including Edwin Hubble’s
work on the distances of work on the distances of
galaxies.
galaxies.
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5m Hale Telescope, Mount Palomar (1948)
5m Hale Telescope, Mount Palomar (1948)

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10m Keck Telescopes, Mauna Kea Hawaii
10m Keck Telescopes, Mauna Kea Hawaii
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Segmented Mirror of the Keck Telescope Segmented Mirror of the Keck Telescope

Extremely Large Telescopes
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• Even larger telescopes – known as Extremely Large
telescopes (or ELTs) are now being designed.
Thirty Thirty Metre Metre Telescope (TMT) Telescope (TMT)
Observing
• How are telescopes
used?