Download Ch 5 notes on telescopes

Ch. 5 notes
http://www.youtube.com/watch?v=qGNgrMNklrc
I. Telescopes
a. Used to capture photons
b. Galileo 1609
c. Increase in size allows large telescopes to
gather and focus more radiation
d. Allowing astronomers to study fainter
objects and obtaining more detailed
information about bright objects
II. Optical Telescopes: the best optical
telescopes on Earth can see down to the arc
second.
a. Reflecting telescopes
i. Use mirrors: primary and secondary
ii. Distance between primary mirror
and focus is called focal length
iii. Images appear flipped upside down
iv. All large modern telescopes on earth
are reflectors
CW: Use pages 109 and 110 as a guide to
illustrate a reflecting telescope
b. Refracting telescopes
i. Uses lenses
ii. Distance between primary lens and
focus is called the focal length
iii. Images appear
_______________________
CW: Illustrate a refracting telescope using pages
109 & 110
CW: these two telescope designs achieve the same
results gathering light from distant objects and
focusing it to form an image to study. However,
as telescopes become larger and larger there are
several important factors to consider when
selecting one optical telescope over another. Read
page 110 to help you decide which one of the two
is better. Give reasons why.
III. Imaging and Non-Imaging detectors
a. Large reflectors are good at forming
images of narrow fields of view when light
strikes the mirror almost parallel
b. Photometer – often spatial detail is lost
but gain more information on intensity
and time variability on pulsating stars
and supernovas
c. Spectrometers – splits light into its
component colors
According to your textbook: Why do all
modern telescopes use mirrors to gather and
focus light?
IV. Telescope Size and Location
a. What does the size of the telescope have to
do with viewing objects in space?
b. Why are optical telescopes on mountain
tops in remote places?
c. Collecting area – the total area of a
telescope capable of gathering radiation
d. Resolution – refers to the ability of any
device to form distinct, separate images of
objects lying close together in the field of
view
e. Diffraction – tendency of light to bend
around corners---causes fuzziness
V. Active and Adaptive Optics: used to
improve resolution of reflecting telescopes
a. Active optics
i. Control temperature and air flow
ii. Change angle of mirror
iii. uses pistons to control the shape of
the mirror to keep it in place
b. adaptive optics flexes the mirror to
deform the mirror’s shape of its surface
VI. Types of telescopes
a. Radio telescopes
i. Extremely large in size because
cosmic radio sources are extremely
faint ( long wavelengths)
ii. Earth-based capable of detecting
cosmic radio waves
iii. Do not require smooth surfaces
iv. Have poor angular resolution because
of diffraction
1. Can be used in tandem
2. Interferometry – a technique that
makes it possible to produce
radio images of angular
resolution higher than the best
optical telescopes
v. Advantages:
1. operate 24hrs day
2. can be made through cloudy
skies and even in bad weather
b. Infrared telescopes
i. Can be Earth-based or in space
ii. Requires cryogenics to reach near
absolute zero temperatures for best
operating conditions
iii. Resemble optical telescopes
iv. Detectors are sensitive to longer
wavelengths which enable us to
“perceive” objects not readily viewed
by optics, much like radio.
v. Often used with optical telescopes
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We build larger and larger telescopes to obtain better resolution even though
we see a small field of view of space.
X-ray telescopes have a barrel-shaped mirror to detect the x-rays because xrays pass through most material.
CW: answer the following questions
1. Give 2 reasons why astronomers are continually building
larger and larger telescopes.
2. List 3 advantages that large reflecting telescopes have over
large refracting telescopes.
3. How do astronomers use active optics to improve
resolution? (need 3 answers)
4. How do astronomers use adaptive optics to improve
resolution?
5. Why do radio telescopes have to be very large?
6. Why do infrared telescopes have to be cooled by
cryogenics?
7. What are the draw-backs to space-based astronomy?
8. In the design of x-ray telescopes, the prime mirror is barrel
shaped in order to capture individual photons. Why is it so
difficult to measure these high energy radiations?