1. Telescopes

2. Objectives
To know the general types of telescopes and the advantages and disadvantages of each one.
To know the primary parts and functions of each part of a telescope.
To know the importance of the diameter of the objective and to know how the magnification of a telescope is related to the focal lengths of the objective and eyepiece.
To know the advantages and disadvantages of earth and space-based telescopes.

3. Galileo Galilei ( )

4. History invented by Dutch lens maker in 1608 Galileo: small 30X scope
Observed the moon and “began” the modern age of Astronomy where measurement was more important than philosophy

5. Galileo noticed moons orbiting Jupiter phases of Venus
craters on the moon
sunspots
This was strong evidence that Copernicus was right although Galileo wasn’t willing to die for it.

6. How a telescope works
gathers light through the objective (mirror or lens)
bigger is better because it gathers more light
ability to see faint objects
focuses light
viewed through an eyepiece (changing the eyepiece changes the magnification)

7. General types of telescopes
Refracting (objective is a lens)
Reflecting (objective is a mirror)
Newtonian
Cassegrain

8. Refractors (glass lens)

9. Advantages and Disadvantages
Easy to use and reliable
Excellent for lunar, planetary.
More expensive
Heavier, longer and bulkier than equivalent Newtonians and Cassegrain.
Color aberration (fuzzy rainbows) due to colors of light bending different amounts.

10. Reflectors (mirror)

11. Advantages and disadvantages
Lowest cost
Reasonably compact and portable.
Excellent for faint deep sky objects such as remote galaxies, nebulae and star clusters.
Reasonably good for lunar and planetary work.
Low in optical aberrations.
More fragile
Large (over 8") are bulky, heavy and tend to be expensive.

12. Cassegrain reflector

13. Schmidtt-Cassegrain

14. Problems with earth-based telescopes
Earth’s atmosphere reflects certain wavelengths
x-rays, gamma rays and most UV light is not transmitted by our atmosphere
Earth’s atmosphere blurs images
the bending of light by the atmosphere depends on the temperature of the “air”
“twinkling” (shimmering) effect
“Light pollution”
Solution? Put the telescope in space.

15. Disadvantages of space-based telescopes
Expensive to launch and maintain
Difficult to repair
Low lifetime

16. Examples of space-based telescopes
Hubble Space Telescope
3 times better resolution
can see fainter objects
Chandra X-ray Observatory
Compton Gamma-Ray Observatory