1. The Largest Telescopes
And
Telescopes made to see
Invisible E-M Radiation

2. Optical Mirrors & Large Scopes
Optical mirrors are silvered on the front.
So light doesn’t go through the glass. Thus…
there is no chromatic aberration and
imperfections in the glass do not matter as much
If parabolic there is no spherical aberration
and there is less sag
Thus the largest astronomical telescopes are all…
prime focus reflectors with parabolic mirrors

3. Multiple Mirror Scopes
Recently to gather more light two or more telescopes are linked by computer.
This creates an image that is brighter and has better resolution than either scope could produce on its own.
The Gemini Telescopes, on the big island of Hawaii are a pair of linked telescopes

4. The Largest Telescopes
For a long time the largest telescope was in So Cal.
First on Mt. Wilson (100” Mirror)
then Mt. Palomar, a 200” objective mirror
For a while the largest was in Russia at 236”
The Largest Telescope now is really four 8m scopes that work together, …the VLT
Or “Very Large Telescope”
It is in Chile, so it can see things in the sky of the Southern Hemisphere

5. Segemented Telescopes
Gran Telescopio Canarias is the world’s largest segmented telescope
Segmented means that its mirror is made in pieces to avoid sag. But all pieces focus to the same point
Its effective diameter is
10.5 m

6. Space Telescopes
Scintillation or “twinkling” of a star is caused by unstable air refracting the star’s light in different directions.
Light is also absorbed and scattered by the atmosphere
This means that even an optical telescope works better in Space. Like
Hubble Space Telescope: For “Deep Space”
Kepler Space telescope: Looking for planet around other stars

7. Radio, X-ray and UV Telescopes
Radio telescopes look and work like a
satellite dish letting us “see” radio waves
The “dish” is the objective.
Infrared, UV and X-ray telescopes also let us “see” those wavelengths
Because the atmosphere absorbs these wavelengths they are best placed in space

8. Detecting Light
At first images in telescopes were seen by one person and had to be hand drawn by the astronomer to be shared.
In the 1800s Film Cameras became available, though they weren’t used in telescopes until the 1900s. Objects then were photographed
Now Charge-Coupled Devices (CCDs) are used to create images and are 20 times more sensitive to light as film. Now objects are digitally imaged

9. Computer aided imaging
Most recently computers have been used to alter images.
i.e.
The light from a star can be subtracted so that we can see the planets orbiting it.
False color images---that let you “see” invisible E-M waves like Infrared