Announcements

1. Announcements • Dr. Smith is at Kitt Peak. He will be back after fall break.

2. Chapter 6:Tools of the Astronomer

3. Telescopes come in three general types Reflectors use mirrors to reflect the light to a focus Refractors use lenses to bend the light to a focus Catadioptric telescopes use both lenses and mirrors

4. The most important property of any telescope is to gather large amounts of light and concentrate it to a focus.

5. Colored Card Questions ClassAction website Telescopes and Astronomical Instruments module Light Gathering Power James Webb Telescope

6. Refraction is the bending of light when it goes from one medium to another Refraction is governed by Snell’s Law: “n” is the index of refraction.

7. If we curve the surface and make a lens, we can get the light to concentrate to a point

8. Colored Card Questions ClassAction website Telescopes and Astronomical Instruments module Refraction…several options Lenses…converging

9. The refracting telescope uses two lenses Since the eye already has a lens, the eyepiece is needed to bring the light rays back to parallel for the eye to see

10. Large refractors can be very long and bulky

11. The Largest Lens is 40” Built in the late 1890’s, it is the last great refracting telescope.

12. Lenses and refractors suffer from Chromatic Aberration This applies to camera lenses, your eye, telescopes and anything else that uses a lens to focus light

13. Correcting for Chromatic aberration can be expensive The compound lens takes two lenses of different materials and combines them to correct for color distortion

14. Color separation is useful in a prism so that we can obtain a spectrum of light Since it is meant to be separated we don’t call it an aberration. Instead, it is called dispersion

15. A diffraction grating works on interference of light waves Diffraction is much more efficient at separating light into its colors than dispersion

16. Unfortunately, diffraction also leads to problems Look closely enough at stars and they aren’t just points of light but rings, too

17. Refractors have many problems They suffer from chromatic aberration They are large and bulky and difficult to maneuver Even the best glass cuts off the IR and UV wavelengths

18. Reflection is the bouncing of light off a surface Mirrors do not suffer from chromatic aberration and they do not cut off long or short wavelengths

19. Colored Card Questions ClassAction website Telescopes and Astronomical Instruments module Reflection…several options

20. A concave mirror focuses light to a focal point Telescope mirrors are made so that the focus is a plane instead of a point

21. There are several types of reflecting telescopes

22. The resolution of a telescope depends on its size and the wavelength of the light Better resolution means smaller angle q

23. The atmosphere limits the resolving power of a ground-based telescope Adaptive Optics can clear up most of the distortions caused by the atmosphere

24. The distortions are caused by differences in the air above the telescope