1. Talking Telescopes Geoff Gaherty

2. Introduction  When to buy?  Telescopes  Mounts  Eyepieces  Accessories  Recommendations

3. When to buy?  Get to know the sky first  Consider buying binoculars first  Sample other people’s telescopes first  Do some research first (the fun kind!): Reading: Harrington: Star Ware (Wiley) Online: www.scopereviews.com Star parties  Then…go shopping (at a telescope store!)

4. Telescopes  Types: refractor reflector catadioptric  Properties aperture focal length focal ratio  Pros and cons

5. Telescope types  Refractor: lens achromatic apochromatic  Reflector: mirror Newtonian  Catadioptric: mirrors with corrector lens Schmidt-Cassegrain Maksutov-Cassegrain

6. Telescope properties  Aperture = diameter of lens/mirror/corrector determines resolution and light gathering  Focal length = effective distance from lens/mirror to eyepiece determines magnification and physical length  Focal ratio = focal length / aperture mainly for astrophotographers

7. Telescope pros and cons  Refractor: simple maintenance high contrast expensive  Reflector: “best bang for the buck!”  Catadioptric: compact size “astrophotography ready”

8. Mounts  Altazimuth Dobsonian simple operation  Equatorial two types: German and fork automatic tracking require polar alignment  Computerized?

9. Computerized mounts  Manual simple, no batteries required  Digital setting circles (DSCs) computer guided/manually powered fast, quiet, low power consumption  GoTo computer guided/motorized slower, noisier, high power consumption

10. How do you find things without a computer?  Learn the constellations  Starhopping figure out the route in a star atlas start from a known bright star practise the route with binoculars retrace the route in the finder scope  Consolmagno & Davis: Turn Left at Orion (Cambridge)  Phil Harrington: Star Watch (Wiley)

11. Eyepieces  Types: Plössl, orthoscopic, wide field  Properties: focal length: determines magnification = telescope f.l. / eyepiece f.l. field of view: apparent vs true eye relief: where to place your eye? exit pupil: light output

12. Magnification  Depends on aperture and seeing conditions  Typically: Low power ≈ aperture (mm) / 5 10-inch aperture (250 mm): 50x Medium power ≈ aperture / 2 10-inch aperture (250mm): 125x High power ≈ aperture (mm) 10-inch aperture (250 mm): 250x  Maximum ≈ 300x limited by atmospheric stability

13. Accessories  Binoculars (10x50)  Barlow lens (2x)  Red flashlight (Rigel)  Star atlas: Pocket Sky Atlas (Sky)  Book: Dickinson: NightWatch (Firefly)  Software: Starry Night

14. Recommendations  10-inch reflector  Dobsonian mount  No computer/Digital setting circles  All of the above accessories