TOOL OF THE TRADE
The whole idea is to collect radiationfrom distant objects, not just observe them.
We have come a long way with telescopes.
MODERN TELESCOPE
What is measured:
1. Brightness
2. Spectra
3. Position
8 meter mirror
at Mauna Kea,
Hawaii
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
LIGHT GATHERING POWER
Light collected brighter image
is proportionalto the collectorarea.
Small changesin collector radius gives large change in number of photons caught. Because A = pr2
REFRACTING TELESCOPES
Remember:
Refraction is
The bending of light becauseof lightchanging speed in different mediums.
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.
TWINKLING OR SCINTILLATION
Temperature and density differencesin pockets of air shift the image of a star.
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.
REFLECTING TELESCOPES
Use Mirrors.
Can make BIG, BIG Mirrors.
Used almost exclusively by Astronomers today.
Multiple
mirrors
and
very
thin.
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.