1. Telescopes and Spacecraft Astronomy 311 Professor Lee Carkner Lecture 7

2. How Do Telescopes Work?  Telescopes:   Focus light to produce an image   Quality and light gathering ability (not magnification) are the most important attributes of a telescope  telescopes make faint things brighter

3. Lenses   Need a lens  Lenses bend light (refraction) and focus all of the light incident on the front to a point (focus) a certain distance behind the lens (focal length)

4. Lenses and Refraction

5. Refracting Telescope   This produces a refracting telescope   mag.= f.l. objective / f.l. eyepiece  in practice the magnification you can achieve is limited by the blurring effects of the Earth’s atmosphere

6. Refracting Telescope

7. Refractors and Reflectors   Makes them  hard to make flawless  heavy and hard to support   large mirrors are easier to make and support

8. Reflecting Telescopes   Problem: The focal point is between the mirror and the sky   Cassegrain Telescope -- secondary reflects light through a hole in the primary, most common type of large telescope

9. Cassegrain Reflecting Telescope

10. Telescope Misconceptions  Magnification is the most important property of a telescope  image quality and light gathering ability (size) are what is important  Astronomers peer through an eyepiece   Telescopes stick out of the dome   Telescopes fold up like a giant pirate’s spyglass 

11. The Electromagnetic Spectrum  Every photon (light particle) has a wavelength which places it in the electromagnetic spectrum   long wavelength -- low energy  short wavelength -- high energy   red -- long wavelength  blue -- short wavelength   So we can explore all physical processes

12. The Electromagnetic Spectrum

13. Telescope Taxonomy  Radio and Millimeter   penetrates atmosphere and everything else  Infrared (IR)   some penetrates atmosphere, but to observe all IR wavelengths need to go into space  Optical   it helps to get above atmosphere (no blurring = sharper images)

14. More Telescope Taxonomy  Ultraviolet (UV)   some penetrates atmosphere, but to observe all UV wavelengths need to go into space  X-ray   all X-rays blocked by atmosphere  Gamma Ray   all Gamma rays blocked by atmosphere

15. Least Energy Orbit   Once in space they coast to the planets, following Kepler’s Laws   An orbit that intersects the Earth’s orbit at one point and the other planet’s orbit at another point (on the opposite side of the Sun)

16. Least Energy Orbit to Mars Sun Earth Mars Spacecraft Orbit  Assume circular orbits for Earth and Mars  a =distance from planet to Sun  a Earth = 1 AU  a Mars =1.5 AU  P 2 =a 3

17. Next Time  Read 15.1-15.4, 6.7  Quiz #1 on Monday  Study hard!

18. Summary  Refracting Telescopes use a lens to bend light to a focus  Reflecting Telescopes use a mirror to reflect light to a focus  Most large research telescopes are reflectors  Astronomers today record and analyze data digitally

19. Summary  To observe the entire electromagnetic spectrum you need many different types of telescopes, some of them in space  Spacecraft have allowed close up study of the planets  Spacecraft reach their destinations by using the gravity of the Sun (or sometimes planets)