Discovering the Universe Eighth Edition

1. Neil F. Comins • William J. Kaufmann III Discovering the Universe Eighth Edition CHAPTER 3 Light and Telescopes

2. WHAT DO YOU THINK? • What is “visible” light? • A wave? A particle? Energy? • What is electromagnetic radiation? • What are the main functions of telescopes? • Why do all research telescopes use mirrors, rather than lenses, to collect light? • Why do stars twinkle?

3. In this chapter you will discover… • The connection between visible light, X-rays, radio waves, & other types of electromagnetic radiation • The debate over what light is and how Einstein resolved it • How telescopes collect and focus light • Why different types of telescopes are used for different types of research

4. In this chapter you will discover… • The limitations of telescopes, especially those that use lenses to collect light • What the new generations of land-based and space-based high-technology telescopes being developed can do • How astronomers use the entire spectrum of electromagnetic radiation to observe the stars and other astronomical objects and events

5. Color is property of light! White light is composed of different colors when shone through glass…. …but the glass is not creating those colors!

6. Observation: Water Waves naturally interfere & create noticeable patterns

7. Young’s Experiment (1801) Light has a wavelike property, too!

8. Observations of Nature • Electricity acts through space over a distance • Lightening, sparks on a doorknob • Magnetism acts through space over a distance • Two magnets attract or repel one another without touching

9. More Observations • If you spin a conductor in a magnetic field, you get electricity! • Electric Generators @ dams & windmills • Portable gas generators • If you run electricity into a coil, you get a magnet! • “Electromagnetic” cranes • Auto solenoids • Electric Motors

10. Maxwell’s Observation • Change Electricity => create magnetism • Change Magnetism => create electricity • Continuously change both, continuously create radiation! • Radiation created moves at “c” – the speed of light!

11. Electro-magnetic radiation!

12. Roemer’s observations of Jupiter’s Moon’s Eclipses demonstrated light moves at a finite speed

13. Non-visible light (beyond the red end of the spectrum) has energy, too!

14. The entire EM Spectrum What we “see” is only a small part of what there is!

15. EM Spectrum Varies by… Size (wavelength, color) Energy How the waves are detected But not…. How fast they move through space!

16. Atmospheric “Windows” to the stars & universe: Visible & Radio light

18. Different types of Reflecting Telescopes

20. Small Telescope image of Andromeda Galaxy

23. Photographs vs. CCD chips vs. Multi-color filtered CCD composite images

24. Refracting Telescopes bend light through lenses Heavy glass lenses, bending different colors to different points (“Chromatic aberration”) & imperfections in glass, limit practical size

27. Functions of Telescopes! • Gather Light • Resolve Sharp Details • Magnify Resulting Images Regardless of Wavelength range & size

28. Orion in UV, Infrared, & Optical Wavelengths

29. #1 Function: Gathering Light • Depends upon the size of the objective mirror or lens. • Light gathering area increases with SQUARE of the diameter • 10 m telescope gather 4x more light than 5m • Subject to interference from other sources!

31. #2 Function: Resolution • Depends upon the size of the objective mirror or lens. • Better resolution with more light • Depends upon wavelength of light, too! • Smaller wavelengths provide smaller details • UV images have more detail than Radio • Also subject to interference

32. Radio Telescopes gather long-wave, low-energy light Poor resolution unless made LARGE!

33. “Seeing” is the ability to resolve small details • Affected by: • Imperfections in optics (shapes of lenses/mirrors) • Atmospheric motion, density, temperature, moisture • Improved by: • Adaptive optics “subtracting out” the atmospheric effects • Getting above atmosphere!

34. Improve seeing by getting above the atmosphere (and gather more types of light, too!)

35. 1 2 3 • Ground-based image of Neptune • Ground-based image with adaptive optics • Hubble Space Telescope image

36. #3 Function: Magnification • Least important • Without a bright, sharp image, no use! • Bigger, Dimmer, Fuzzier! • Depends upon EYEPIECE used • Small scopes: $50-500 each • Easily swapped to magnify images • Depends upon telescope geometry, too

37. Active & Adaptive Optics! • Active optics (1980’s) • Put actuators on segmented mirrors to “bend” them to the right shape • Keck, NTT, VLT Telescopes • Adaptive optics (1990’s to present) • “Deform” mirror in real time to compensate for atmospheric motion • Laser Guide Stars

38. VLT in Chile • (4) combined 8.2 m telescopes • Tracking motions of stars at Milky Way Center

39. SALT in Africa • Largest current “single” surface scope

40. Next Generation Space Telescope • NASA’s next great observatory • Bigger than Hubble

41. Seeing in Stereo!

42. Interferometry – Combining signals simultaneously from 2 or more scopes

43. Visible & Radio wave views of Saturn

48. Why build telescopes at all? We already have enough! Why do we need a more detailed picture of Mars? Who cares? This cost $100 Million dollars? You’ve got to be kidding me…

49. Summary: The Nature Of Light • Photons, units of vibrating electric and magnetic fields, all carry energy through space at the same speed, the speed of light (300,000 km/s in a vacuum, slower in any medium). • Radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X rays, and gamma rays are the forms of electromagnetic radiation. They travel as photons, sometimes behaving as particles, sometimes as waves.

50. The Nature Of Light • Visible light occupies only a small portion of the electromagnetic spectrum. • The wavelength of a visible light photon is associated with its color. Wavelengths of visible light range from about 400 nm for violet light to 700 nm for red light. • Infrared radiation and radio waves have wavelengths longer than those of visible light. Ultraviolet radiation, X rays, and gamma rays have wavelengths that are shorter.