1. Telescopes

2. Galileo Galilei ( )

3. History invented by Dutch lens maker in early 1600’s.
Galileo: small 30X scope
Observed the moon and “began” the modern age of Astronomy where measurement was more important than philosophy

4. How a telescope works
gathers light through the objective (mirror or lens)
wider is better because it gathers more light
ability to see faint objects increases proportionally with the square of the radius of the objective
focuses light
viewed through an eyepiece (changing the eyepiece changes the magnification)

5. Major Telescope Parts
Eyepieces
Tripod & Mount
Tube Assembly
Focuser

6. General types of telescopes
Refracting (objective is a lens)
Reflecting (objective is a mirror)
Newtonian (reflects once before hitting eyepiece)
Cassegrain (reflects twice beefore hiting eyepiece)

7. Refractors (glass lens)

8. Refractors

9. Advantages and Disadvantages
Easy to use and reliable
High contrast images with no secondary mirror or diagonal obstruction.
Sealed optical tube reduces image degrading air currents and protects optics.
More expensive per inch of aperture
Heavier, longer and bulkier than equivalent aperture reflectors.
Small apertures
Less suited for viewing small and faint deep sky objects.
Color changes due to colors of light bending different amounts.

10. Reflectors (mirror)

11. Cassegrain reflector

12. Reflectors

13. Advantages and disadvantages
Lower cost per inch of aperture
Reasonably compact and portable up to focal lengths of 1000mm.
Excellent for faint deep sky objects such as remote galaxies, nebulae and star clusters.
Reasonably good for lunar and planetary work.
Open optical tube design allows image-degrading air currents and air contaminants
More fragile
Large apertures (over 8") are bulky, heavy and tend to be expensive.

14. Catadioptric telescopes
Best all-around, all-purpose telescope design. Combines the optical advantages of both lenses and mirrors while canceling their disadvantages.
Sharp images over a wide field.
Very good for lunar, planetary and binary star observing or photography.
Closed tube design reduces image degrading air currents.
Most are extremely compact and portable.
Large apertures at reasonable prices and less expensive than equivalent aperture refractors.

15. Catadioptric Telescopes

16. 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.

17. Gray = amount transparant

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

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