1. NATS 1311 - From the Cosmos to Earth The Doppler Effect

2. NATS 1311 - From the Cosmos to Earth Sound Each circle represents the crests of sound waves going in all directions from the train whistle. The circles represent wave crests coming from the train at different times, say, 1/10 second apart. If the train is moving, each set of waves comes from a different location. Thus, the waves appear bunched up in the direction of motion and stretched out in the opposite direction. The Doppler Effect - Wavelength Shift Due to Motion.

3. NATS 1311 - From the Cosmos to Earth Hearing the Doppler Effect Animation

4. NATS 1311 - From the Cosmos to Earth Doppler Shift vs Velocity Animation

5. NATS 1311 - From the Cosmos to Earth Doppler Shift for Light We get the same effect for light as for sound.

6. NATS 1311 - From the Cosmos to Earth Doppler Effect for Light Animation

7. NATS 1311 - From the Cosmos to Earth The Doppler Effect 1. Light emitted from an object moving towards you will have its wavelength shortened. 2. Light emitted from an object moving away from you will have its wavelength lengthened. 3. Light emitted from an object moving perpendicular to your line-of- sight will not change its wavelength. BLUESHIFT REDSHIFT

8. NATS 1311 - From the Cosmos to Earth Doppler Shift of Emission Lines Animation

9. NATS 1311 - From the Cosmos to Earth  v c = The amount of spectral shift tells us the velocity of the object:

10. NATS 1311 - From the Cosmos to Earth The Doppler shift only tells us part of the object’s full motion - the radial part or the part directed toward or away from us.

11. NATS 1311 - From the Cosmos to Earth Measuring Rotational Velocity Doppler shift can be used to tell us how fast an object is rotating: As an object rotates, light from side rotating toward us is blueshifted - light from side rotating away from us is redshifted. Spectral lines appear wider - the faster it rotates, the wider are the spectral lines.

12. NATS 1311 - From the Cosmos to Earth 1. Imaging –use a camera to take pictures (images) –Photometry  measure total amount of light from an object 2.Spectroscopy –use a spectrograph to separate the light into its different –wavelengths (colors) 3. Timing –measure how the amount of light changes with time (sometimes in a fraction of a second) Uses of Telescopes

13. NATS 1311 - From the Cosmos to Earth Nonvisible Light Special detectors/receivers record light invisible to the human eye - gamma rays, x-rays, ultraviolet, infrared, radio waves. - each type of light can provide information not available from other types. Digital images are reconstructed using false-color coding so that we can see this light. Chandra X-ray image of the Center of the Milky Way Galaxy

14. NATS 1311 - From the Cosmos to Earth The Crab Nebula VisibleInfrared Radio Waves X-rays

15. NATS 1311 - From the Cosmos to Earth Earth’s atmosphere causes problems for astronomers on the ground: Bad weather makes it impossible to observe the night sky. Man-made light is reflected by the atmosphere, thus making the night sky brighter. –light pollution The atmosphere absorbs light - dependent on wavelength Air turbulence in the atmosphere distorts light. –That is why the stars appear to “twinkle”. –Angular resolution is degraded. Atmospheric Effects

16. NATS 1311 - From the Cosmos to Earth Light Pollution

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18. Atmospheric Absorption of Light Earth’s atmosphere absorbs most types of light. –good thing it does, or we would be dead! Only visible, radio, and certain IR and UV light make it through to the ground. To observe the other wavelengths, we must put our telescopes in space!

19. NATS 1311 - From the Cosmos to Earth Space Astronomy

20. NATS 1311 - From the Cosmos to Earth Space Based Telescopes Chandra X-ray Obs.Hubble Space Telescope Compton Gamma Ray Obs.Spitzer Space Telescope (IR) FUSE (Far UV)

21. NATS 1311 - From the Cosmos to Earth Ultraviolet Astronomy Ultraviolet radiation traces hot (tens of thousands of degrees), moderately ionized gas in the Universe. UV radiation with < 290 nm is completely absorbed in the ozone layer of the atmosphere. Therefore, UV astronomy has to be done from satellites. - Several successful ultraviolet astronomy satellites: IRAS, IUE, EUVE, FUSE

22. NATS 1311 - From the Cosmos to Earth X-Ray and Gamma Ray Astronomy X-rays and gamma rays are completely absorbed in the atmosphere. - therefore, X-ray and gamma ray astronomy has to be done from satellites. X-rays trace hot (million degrees), highly ionized gas in the Universe. Gamma-rays: most energetic electromagnetic radiation - traces the most violent processes in the Universe

23. NATS 1311 - From the Cosmos to Earth The Hubble Space Telescope is 43.5 ft long and weighs 24,500 lbs. Its primary mirror is 2.4 m (7 ft 10.5 in) in diameter. - avoids turbulence in the Earth’s atmosphere - extends imaging and spectroscopy to infrared and ultraviolet The Hubble Space Telescope

24. NATS 1311 - From the Cosmos to Earth Radio Astronomy Recall: Radio waves of ~ 1 cm – 1 m also penetrate the Earth’s atmosphere and can be observed from the ground.

25. NATS 1311 - From the Cosmos to Earth Radio Telescopes Large dish focuses the energy of radio waves onto a small receiver (antenna) Amplified signals are stored in computers and converted into images, spectra, etc.

26. NATS 1311 - From the Cosmos to Earth Radio Telescopes 305-meter radio telescope at Arecibo, Puerto Rico The wavelengths of radio waves are long. So the dishes which reflect them must be very large to achieve any reasonable angular resolution.

27. NATS 1311 - From the Cosmos to Earth Radio Interferometry The Very Large Array (VLA): 27 dishes are combined to simulate a large dish of 36 km in diameter. Even larger arrays consist of dishes spread out over the entire U.S. (VLBA = Very Long Baseline Array) or even the whole Earth (VLBI = Very Long Baseline Interferometry)!

28. NATS 1311 - From the Cosmos to Earth Science of Radio Astronomy Radio astronomy reveals several features, not visible at other wavelengths: - neutral hydrogen clouds (which don’t emit any visible light), containing ~ 90 % of all the atoms in the Universe. - molecules (often located in dense clouds, where visible light is completely absorbed). - Radio waves penetrate gas and dust clouds, so we can observe regions from which visible light is heavily absorbed.

29. NATS 1311 - From the Cosmos to Earth Atmospheric Distortion Animation Atmospheric Distortion The turbulence (ever-changing motion) of the atmosphere causes distortion - twinkling of starlight. Bends light in constantly shifting patterns. Like looking down the road on a hot day and seeing distant cars rippling and distorting. Why best viewing is when it is cold and calm.

30. NATS 1311 - From the Cosmos to Earth Adaptive Optics (AO) It is possible to “de-twinkle” a star. The wavefronts of a star’s light rays are deformed by the atmosphere. By monitoring the distortions of the light from a nearby bright star (or a laser): –a computer can deform the secondary mirror in the opposite way. –the wavefronts, when reflected, are restored to their original state. AO mirror offAO mirror on Angular resolution improves. These two stars are separated by 0.38  Without AO, we see only one star.

31. NATS 1311 - From the Cosmos to Earth