1. Light and Telescopes

2. What do you think? What is the main purpose of a telescope?
Why do stars twinkle?

3. What is Light and Why Would Astronomers Want to Study the Properties of Light?
Sometimes we say light is made of waves
Sometime we say light is made of particles called photons
Moves very fast, at miles per second
300,000 km per second
consider a prism ...

4. If you pass white light through a prism, it separates into its component colors.
long wavelengths
short wavelengths
R.O.Y. G. B.I.V
spectrum

5. Analyzing The Properties of Light
Visible Light is but one part of the entire electromagnetic (EM) spectrum.
EM Spectrum includes all kinds of light
radio waves (all light moves at the same speed -
micro waves light speed)
infrared light
visible light
ultra violet light (some light photons have
x rays shorter wavelengths
gamma rays and more energy than others)

6. Visible light is only one type of electromagnetic radiation emitted by stars
Each type of EM radiation travels at exactly the same speed - the speed of light!

7. Not all EM radiation can penetrate Earth’s atmosphere.

8. Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth’s atmosphere.

9. SOFIA - the Stratospheric Observatory for Infrared Astronomy

10. Observations at other wavelengths are revealing previously invisible sightsUV
infrared
Map of Orion region
Ordinary visible

11. Consider Orion in Different Wavelengths of Light!

12. http://www. cnn. com/2001/LAW/02/20/scotus. heatdetector. 01. ap/index

13. Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds

14. TODAY’S Sun as seen in visible light from Earth and from space in X-rays by satellites

15. Observations at wavelengths other than visible light are revealing previously invisible sights
Visible light image
radio wavelength image

16. High Energy Gamma Rays - Compton Gamma Ray Observatory (GRO) Satellite

17. The Sky’s emission of Gamma Rays

18. But, we receive GRBs from every direction !!
The fact that GRBs come from every direction imply that GRBs don’t come from our galaxy, but from other galaxies spread in every direction!

19. Radio wavelength observations are possible from Earth’s surface

20. The Very Large Array (VLA) in New Mexico

21. Different types of EM radiation require different types of telescopes
A refracting telescope uses a lens to concentrate incoming light
A reflecting telescope uses mirrors to concentrate incoming starlight

22. Analyzing Spectra: The Properties of Light
Visible Light is one part of the electromagnetic (EM) spectrum.
EM radiation is described as a wave with wavelengths in the range 1x10-15 m to 100 m.
Visible light is only a tiny small part of the entire electromagnetic spectrum.
Little bits of light are called photons.

23. Dividing Light Into a Spectrum
Astronomers separate out light into its individual components using a diffraction grating or using a prism - then they analyze each part independently!

24. blue 4600 A 81
Filter
Detector 81

25. blue 4600 A 81 green 5300 A 85 Filter Detector 85

26. blue 4600 A 81 green 5300 A 85 yellow 5800 A 83 Filter Detector 83

27. blue 4600 A 81 green 5300 A 85 yellow 5800 A 83 orange 6100 A 78
Filter
Detector 78

28. The spectrum is continuous. green 5300 A 85 yellow 5800 A 83
blue 4600 A 81
The spectrum is continuous.
green 5300 A 85
yellow 5800 A 83
orange 6100 A 78
Filter
red 6600 A 70
Detector 70 UV IR

29. Spectra
Most light sources contain energy in lots of different wavelengths.
We can measure the brightness in various wavelength bands--the result is called the spectrum.
The spectrum (total character of light emitted) can tell us a lot about a source.

31. A refracting telescope uses a lens to concentrate incoming light
Similar to a magnifying glass

33. A larger objective lens provides a brighter (not bigger) image

34. lenses reverse images

35. Three main functions of a telescope
Brighten
(called light gathering power)
See fine detail
(called resolution)
and least important,
Magnify
magnification = (objective lens focal length / eyepiece lens focal length)

36. Functions of a Telescope
To gather light.
want a large objective
range of few inches to 10 meters!!
To resolve fine detail.
limited by size and atmospheric “seeing”
To magnify
least important
about 50x per inch of aperture (rule of thumb)
1: List the major regions of the electromagnetic spectrum in order of wavelength and give common examples of each.
2: List the colors of the visible spectrum in order of wavelength.
3: Name the two main classes of telescopes and describe the physical laws that each uses to form images.
4: Describe how the focal length and diameter of a telescope influence its angular resolution, light-gathering power, and magnifying power.
5: Draw a refracting telescope and reflecting telescopes with Newtonian, Cassegrain, prime, and coude’ focus locations, showing the path of parallel light rays through each.
6: Compare the merits and deficiencies of the two major classes of telescopes.
7: Discuss the similarities and differences of radio telescopes and optical telescopes.
8: List the advantages of orbiting telescopes over Earth-bound telescopes in detecting electromagnetic radiation in each of the major spectral regions.
9: Identify examples of observations impossible from the ground that have been made by the Hubble Space Telescope.

37. Refracting telescopes have drawbacks
Spherical aberration
Chromatic aberration

38. Special achromatic compound lenses and lens coatings can often fix this aberration

39. Refracting telescopes have drawbacks
Spherical aberration
Chromatic aberration
Sagging due to gravity distorting the lens
Unwanted refractions
opaque to certain wavelengths of light
Yerkes Observatory - 40-inch Refracting Telescope: The Largest Refracting Telescope in the World

40. Reflecting telescopes use mirrors to concentrate incoming starlight

41. Cassegrain focus Newtonian Focus coude’ focus Prime Focus

42. Astronomer’s face two major obstacles in observing the stars
Light Pollution from Cities
Effects of Twinkling from Earth’s atmosphere

43. Tucson, Arizona in 1959 and 1980

44. Earth’s atmosphere hinders astronomical research
Image of stars taken with a telescope on the Earth’s surface
Same picture taken with Hubble Space Telescope high above Earth’s blurring atmosphere

45. Rapid changes in the density of Earth’s atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle.

46. Advanced technology is spawning a new generation of equipment to view the universe
CCDs (charge-coupled devices)
Large telescopes on remote mountain tops
Mauna Kea in Hawaii
Cerro Pachon in Chile
Adaptive Optics to counteract the blurring of Earth’s atmosphere
Orbiting space observatories

47. A Charge-Coupled Device (CCD)

48. Ordinary Photographs vs. CCDs
Film (negative) CCD (negative) CCD (positive)
Same integration (I.e. exposure) time.
Different quantum efficiency: Film 1% CCD 70%

49. Matching 10-m, multiple mirror Keck Telescopes in Hawaii with adaptive optics

50. High above Earth’s atmosphere, the Hubble Space Telescope provides stunning details about the universe

51. What did you think? What is the main purpose of a telescope?
A telescope is designed to collect as much light as possible. It also improves resolution and magnifies images.
Why do stars twinkle?
Rapid changes in the density of Earth’s atmosphere cause passing starlight to change direction, making stars appear to twinkle.