A simple without much math details about generalities of telescopes for a high school beginning level astronomy class.

2. TOOL OF THE TRADE
The whole idea is
to collect radiation
from distant
objects, not just
observe them.
We have come a long way with telescopes.

3. Now telescopes are not only on earth
but in space as well.

4. MODERN TELESCOPE
What is measured:
1. Brightness
2. Spectra
3. Position
8 meter mirror
at Mauna Kea,
Hawaii

5. TOOLS:
Astronomers are rarely at the
“eyepiece.” They are on computer
terminals.

6. POWERS OF A TELESCOPE
• Collecting Power
-Bigger the telescope, more light
collected.
• Focusing Power
-Use mirrors or lenses to bend the
path of light rays to create images
• Resolving Power
- Picking out the details of an image

7. LIGHT GATHERING POWER
Light collected brighter image
is proportional
to the collector
area.
Small changes
in collector
radius gives large change in number of
photons caught. Because A = pr2

8. REFRACTING TELESCOPES
Remember:
Refraction is
The
bending of
light because
of light
changing
speed in different mediums.

9. REFRACTION IS RESPONSIBLE FOR
Dispersion: causes
different colors to
travel at different
speeds through the
same material. Responsible
for the
distortion of
the Sun near
the horizon.

10. TWINKLING OR SCINTILLATION
Temperature and
density differences
in pockets of air
shift the image of
a star.

11. REFRACTING TELESCOPES
Telescopes that use lenses to collect
and focus light called refractors.
Disadvantages:
1. Large lens: Expensive
2. Large lens: sags in the center
3. Dispersion causes images to have
colored fringes.
4. Many lens materials absorb short
wavelength light.

12. CHROMATIC ABERRATION
The colors of white light refract
differently so they focus
differently.

13. REFLECTING TELESCOPES
Use Mirrors.
Can make BIG, BIG Mirrors.
Used almost exclusively by
Astronomers today.
Multiple
mirrors
and
very
thin.

14. REMEMBER RESOLVING POWER?
For a given wavelength resolution is
increased for a larger telescope.
Interferometers will increase
resolution by combining
observations
from two or
more
widely spaced
telescopes.

15. INTERFEROMETER
DIFFERENCE
McGraw Hill Picture
See
two
stars
in B.

16. LIGHT GATHERING POWER
Compare Two Telescopes: A to B
LGA = Diameter of A
LGB Diameter of B
2

17. Example: Suppose we compare a
6 cm telescope with a 32 cm
telescope. How much more light
will the large telescope gather?
Use A as the larger telescope:
(32/6)2 = 28.6 times