1. Unit 3 Telescopes

2. Optical Telescopes Two basic types – Refractors – Reflectors

3. Refractors Uses lenses to gather and concentrate light

4. Refractors Advantages: – Refractor telescopes are rugged – Lenses inside the tube is sealed so it rarely needs cleaning – images are steadier and sharper Disadvantages: – chromatic aberration – Lens supported only at the ends, lens will sag – Expensive, heavy

5. Refractor

6. Reflectors Uses a curved mirror to focus incoming light

7. Reflectors Advantages: – Do not suffer from chromatic aberration – Can be made very BIG! – Less expensive, lighter Disadvantages: – Optics need more frequent alignment – Open to the outside, need frequent cleaning – Secondary mirror can produce diffraction effects

8. Reflector

9. Types of Reflectors Gregorian Newtonian Cassegrain

10. Schmidt-Cassegrain

11. Telescope magnification Magnification = focal length of telescope / focal length eyepiece e.g. focal length of telescope = 1000 mm focal length of eyepiece = 30 mm magnification = 1000 mm/ 30 mm = 33

12. Brightness The observed brightness of an object is directly proportional to the area of the telescope mirror, e.g. a 5 meter telescope will have a light gathering capacity 25 times (5 2 ) greater than a 1 meter telescope

13. History of Large Telescopes William Herschel (late 1700s)

14. Mt. Wilson (1917) – 100 inch

15. Hale (1948) – 200 inch

16. Space Telescopes outside the distortion of Earth's atmosphereEarth's atmosphere extremely sharp images almost no background lightbackground

17. Space Telescopes Hubble Spitzer Chandra

18. Kepler Space Telescope Designed to discover Earth-like planets

19. Herschel Space Observatory Launched in 2009 by the European Space Agency Sensitive to Infrared radiation

20. Image Acquisition & Processing Charge-coupled devices (CCDs)  computer (very efficient)

21. Radio Astronomy

22. How to pick a telescope Start by using your bare eyes Next, move up to binoculars When you’re ready for a telescope, read/ research

23. Choosing the right telescope Performance Purpose Portability Light Pollution Price

24. All other things being equal, the greater the mirror/ lens diameter the greater the light gathering ability Primary Mirror Size Square Inches of Aperture 4" 12 6 28 8 50 10 78 12 113 http://www.astronomics.com/main/category.asp/catalog_name/Astronomics/category _name/How%20to%20pick%20a%20telescope/Page/1 http://www.astronomics.com/main/category.asp/catalog_name/Astronomics/category _name/How%20to%20pick%20a%20telescope/Page/1