Download astronomy notes: ground-based telescopes

ASTRONOMY NOTES: GROUND-BASED TELESCOPES
Atmospheric Windows
Areas in the EM spectrum where the
atmosphere is transparent and the radiation
can pass through to the Earth’s surface.
Earth has 2 atmospheric windows
•
Radio
•
Visible
Therefore, there are 2 main types of groundbased telescopes.
Optical Telescopes
Focus light into an image. Light is collected by
lens or mirror
OPTICAL TELESCOPES
Basic Optics: Reflecting Telescope
Basic Optics: Refracting Telescope
How it works
Problems
Refracting Telescope
Reflecting Telescope
Bends light through a lens to form an
Curved mirror reflects light to form an
image
image
Eyepiece magnifies the light
Eyepiece magnifies the light
•
UV light is absorbed by lens and
dims the image
•
Lens must be large to improve
magnification
Chromatic Aberration
o
Very expensive
o
Lens can only be supported
from sides and may sag
under its own weight
•
Difficult and expensive to make
lens without defects
•
Chromatic aberration
Reflecting telescope is an improvement of the refracting telescope
•
Light is reflected before passing through lens ! no chromatic aberrations
•
Do not need high quality optical glass
o
Cheaper
o
Can be made larger ! bigger mirror, collects more light = better image
•
Mirror can be supported from the back ! will not sag
•
Tend to be shorter
Check Point
1. What does refract mean?
a. Light rays are absorbed as they pass into a different medium
b. Light rays bounce back as they pass into a different medium
c.
Light rays change direction as they pass into a different
medium
2. Which way do light rays bend through a convex lens?
a. Together at a converging point
b. Away from each other – they diverge
c.
They do not pass through, they bounce back
3. What types of lenses are used in refracting telescopes?
a. Converging
b. Diverging
c. No lenses are used
Radio Telescopes
Used to study naturally occurring radio waves from stars, galaxies,
quasars and other celestial objects.
Has two main parts
•
Primary reflector surface
•
Antenna
Radio Telescopes: Advantages
• Can be used in poor weather conditions (cloudy,
etc)
• Can be used during the day
Radio Telescopes: Disadvantages
• Radio waves may be large, so radio
telescopes must be large
• Very expensive