light and telescopes astronomy science.ppt
- 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 186 000 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. R.O.Y. G. B.I.V spectrum long wavelengths short wavelengths
- 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 sights UV Ordinary visible infrared Map of Orion region
- 11. Consider Orion in Different Wavelengths of Light!
- 13. Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds http://oposite.stsci.edu/pubinfo/pr/97/13/A.html
- 14. TODAY’S Sun as seen in visible light from Earth and from space in X-rays by satellites http://solar.physics.montana.edu/tslater/real-time/
- 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!
- 25. Filter Detector 85 blue 4600 A 81 green 5300 A 85
- 26. Filter Detector 83 blue 4600 A 81 green 5300 A 85 yellow 5800 A 83
- 27. Filter Detector 78 blue 4600 A 81 green 5300 A 85 yellow 5800 A 83 orange 6100 A 78
- 28. Filter Detector 70 blue 4600 A 81 green 5300 A 85 yellow 5800 A 83 orange 6100 A 78 red 6600 A 70 The spectrum is continuous. UV IR
- 29. Spectra 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
- 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)
- 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. Newtonian Focus Prime Focus Cassegrain focus coude’ 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
- 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.
Editor's Notes
- #44: 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.