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

2. How Do We Learn About The Solar System?  View from Earth:    View remotely:   Other methods:   find pieces of solar system that have visited us (meteorite)

3. How Do Telescopes Work?  Telescopes:     Light gathering ability (not magnification) is the most important attribute of a telescope  telescopes make faint things brighter

4. Lenses  If you point an empty tube at an object, you may be gathering lots of light, but it doesn’t get to your eye   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)

5. Lenses and Refraction

6. Refracting Telescope  If you put a second lens (eyepiece) behind the first lens(objective), you can magnify the image   Magnification is equal to the ratio of the focal lengths  mag.= f.l. objective / f.l. eyepiece 

7. Refracting Telescope

8. Giant Refractor at Yerkes Observatory

9. Refractors and Reflectors  It is hard to make large refracting telescopes   A curved mirror can be used to gather and focus the light instead (reflecting telescope) 

10. Reflecting Telescopes  A curved mirror (the primary mirror) reflects light so that it is focused  Problem: The focal point is between the mirror and the sky   Cassegrain Telescope --

11. Cassegrain Reflecting Telescope

12. Path of Light  Light beams enter from infinity and are initially parallel   The eyepieces then magnifies the point image by taking the divergent rays from the focal and making them parallel again 

13. 5 meter Hale Telescope at Mount Palomar

14. The Hobby-Eberly Telescope

15. What Can a Telescope Do?  Imaging --  Photometry –  Spectroscopy --  A spectrum is the amount of light at each wavelength.  The shape of the spectrum tells you about the temperature, composition and motions of the object

16. Types of Detectors  Eye -- limited ability to do photometry or spectroscopy, data is difficult to analyze (must write down what you see)  Photographic plate --  Charge Coupled Device (CCD) -- more sensitive and easier to use than a plate, allows you to store and reduce data electronically 

17. Telescope Misconceptions  Magnification is the most important property of a telescope   Astronomers peer through an eyepiece   Telescopes stick out of the dome   Telescopes fold up like a giant pirate’s spyglass 

18. The Electromagnetic Spectrum  Every photon (light particle) has a wavelength which places it in the electromagnetic spectrum  The wavelength relates to energy  long wavelength --  short wavelength --  We see different wavelengths of visible light as colors  

19. The Electromagnetic Spectrum

20. Observing at Different Wavelengths  Planets, stars and galaxies produce radiation at many different wavelengths in many different ways   Many types of light don’t penetrate the Earth’s atmosphere and need to be observed from orbit 

21. Telescope Taxonomy  Radio and Millimeter -- penetrates atmosphere and everything else   Example:  Infrared (IR) -- we feel as heat   Example:  Optical -- what our eyes can see   Example --

22. More Telescope Taxonomy  Ultraviolet (UV) -- high energy radiation, causes sunburn   Example --  X-ray -- very high energy   Example --  Gamma Ray -- the highest energy   Example --

23. The VLA

24. Hubble Space Telescope

25. Spacecraft  Since the 1960’s we have sent probes to study the planets close up  Types of spaces probes:  Fly-by --  Example:  Orbiter --  Example:  Lander --  Example:

26. Getting to The Planets  Spacecraft don’t zoom around the Solar System like in science fiction   Use small thrusters to maneuver (remember Newton’s First Law -- Inertia) 

27. Least Energy Orbit  Once the spacecraft is out of the Earth’s gravity well, a little nudge with the thrusters will send it on its way   Easiest way to get to a planet is a least energy orbit 

28. Least Energy Orbit to Mars Sun Earth Mars Spacecraft Orbit Time to get to Mars     a Earth = 1 AU  a Mars =1.5 AU 

29. 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

30. 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)