Astronomy 1010-H Planetary Astronomy Fall_2014 Day-19

1. Astronomy 1010-H Planetary Astronomy Fall_2014 Day-19

3. Course Announcements • SW Ch. 5: Fri. 10/10 (see, it did change) • SW Ch. 6: Fri. 10/24 (subject to change) • Exam-2: Friday, Oct. 10 (Ch. 3, 4, 5) • Bring L-T books for collection • Read chapters 5, 6

4. Telescopes & Instruments

5. The telescope is the astronomer’s most important tool. • Purpose: to gather light of all kinds. • Two kinds of optical telescopes: reflecting and refracting. • Invented in 1608 by Hans Lippershey.

6. 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

7. Telescopes • Telescopes have three functions: • Gather light • LGP ∝ Area = πR2 • Resolve objects • Θ = 2.06 X 105 (λ/D) • Magnify EXTENDED objects

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

9. 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.

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

11. Refracting telescopes use lenses. • Objective lens: refracts the light. • Aperture: size of the objective lens (larger aperture gathers more light). • The objective lens is placed in the aperture.

12. 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

13. Large refractors can be very long and bulky

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

15. 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

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

17. 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

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

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

20. 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

21. Reflecting telescopes use mirrors. • There are primary and secondarymirrors. • Focal length is determined by the path the light takes reflecting off the mirrors.

22. 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

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

24. Reflecting Telescopes Suffer From Spherical Aberration

25. There are several types of reflecting telescopes