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GE 150 Astronomy

GE 150 Astronomy. Week #10 March 26 , 2013. What can we learn by analyzing starlight?. A star’s temperature A star’s chemical composition. - peak wavelength of the spectral curve. - dips in the spectral curve or the lines in the absorption spectrum. A star’s motion. The Doppler Effect.

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GE 150 Astronomy

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  1. GE 150 Astronomy Week #10 March 26, 2013

  2. What can we learn by analyzing starlight? • A star’s temperature • A star’s chemical composition - peak wavelength of the spectral curve - dips in the spectral curve or the lines in the absorption spectrum • A star’s motion

  3. The Doppler Effect • Definition:“The change in wavelength (of either light or sound) due to the relative motion between the source and the observer along the line of sight.”

  4. Astronomers use the Doppler Effect to learn about the relative motions of stars, and other astronomical objects

  5. Real Life Examples of Doppler Effect • Doppler Radar (for weather) • Airplane radar system • Ok, anything with radar • Radar gun, used by Law Enforcement Officers…

  6. The Doppler Effect • When something which is giving off light moves towardsorawayfrom you, the wavelength of the emitted light is changed or shifted V=0

  7. The Doppler Effect • When the source of light is moving away from the observer the wavelength of the emitted light will appear to increase. We call this a “redshift”. Unshifted

  8. The Doppler Effect • When the source of light is moving towards the observer the wavelength of the emitted light will appear to decrease. We call this a “blueshift”. Unshifted

  9. “Along the line of sight” means the Doppler Effect happens only if the object which is emitting light is moving towards you or away from you. An object moving “side to side” or perpendicular, relative to your line of sight, will not experience a Doppler Effect. Unshifted

  10. Astronomy Application V=0

  11. Doppler Shifts • Redshift (to longer wavelengths): The source is moving awayfrom the observer • Blueshift (to shorter wavelengths): The source is moving towards the observer Dl = difference of shifted and unshifted l0= wavelength when source is not moving v = velocity of source c = speed of light

  12. Doppler Effect in Light H alpha λ0=656 nm Δλ = 22 nm c

  13. Stars

  14. Stars • Start by studying the closest star: the Sun • What tools do have so far: • Blackbody Spectrum/Wien’s Law • How energy is distributed with wavelength • Surface Temperature • Emission/Absorption lines • Composition • Use these and some new concepts to determine structure of the Sun

  15. Our Star, the Sun

  16. The Sun: the largest object in Solar System • The Sun contains more than 99.85% of the total mass of the solar system • Allthe planets in the solar system together would not fill up the volume of the Sun • 110 Earths or 10 Jupiters fit across the diameter of the Sun

  17. Core Radiative zone Convective zone The Sun’s interior has three layers: Energy generated in the core of the Sun propagates outward through these different layers, and finally, through the atmosphere of the Sun. This process takes 100 thousand years or more.

  18. Energy Transport in the Sun • The Core • Source of all the Sun’s Energy • Only 10 % of the Sun’s mass • Only part of the Sun available for “fuel”

  19. Energy Transport in the Sun • RadiativeZone • Energy from the core is transported outward by of photons (i.e. radiation) • Cooler than core but gas is still very hot and very dense • Photons (x & gamma rays) are absorbed/re-emitted every 1 cm

  20. Energy Transport in the Sun • Convection Zone • hot gas rises, dumps its energy onto the surface and then sinks • similar to a pot of boiling water

  21. The Sun’s atmosphere also has three layers… Photosphere - the layer we see: 5800 K Sun is opaque below this layer Chromosphere - the red layer observed using a hydrogen filter: 10,000 K Corona- the incredibly thin outer atmosphere: 1,000,000 K Last two layers only visible during eclipses Corona Chromosphere Photosphere

  22. Hotter gas here is rising (blueshifted) The photosphere is the visible layer of the Sun Cooler gas here is falling (Redshifted) Granulation caused by convection

  23. Sunspots • Sunspots are highly localized cool regions in the photosphere of the Sun • First observed by Galileo in 1609 • Can be many times larger than the Earth • Appear darker, in contrast, because they cooler than surroundings 4500 K

  24. Galileo used the movement of sunspotsacross the Sun’s surface reveals that the it rotates once in about … 4 weeks

  25. The annual change in numbers of sunspots reveals that the Sun experiences an 11-year Sun Spot cycle Next Peak 2013-2014

  26. Sunspots: Max Vs Min July 19, 2000 March 18, 2009

  27. An Ultraviolet look… July 19, 2000 March 18, 2009

  28. The Sun goes through periods of relative activity and inactivity The Sun in X-Rays

  29. Magnetic field lines connect sunspots on the Sun’s photosphere

  30. Solar magnetic fields also create other atmospheric phenomena prominences

  31. Gas trapped in Sunspot’s magnetic field

  32. prominences solar flares Solar magnetic fields also create other atmospheric phenomena

  33. Above the photosphere, the chromosphere is characterized by its redcolor – from Haemission. 1500 km Chromosphere satisfies the conditions for Kirchkoff’s 2nd Law

  34. The corona, the outermost part of the Sun’s atmosphere, is characterized by its high temperature and low density It expands into space as a stream of charged particles known as the solar wind

  35. Solar magnetic fields also create other atmospheric phenomena prominences solar flares coronal mass ejections (CMEs)

  36. http://www.spaceweather.com/

  37. The most powerful solar flare in 14 years, .. erupted from sunspot 486 in late October of 2003. The explosion hurled a coronal mass ejection (CME) almost directly toward Earth, which triggered bright auroras when it arrived on Earth.

  38. The Earth’s magnetic field is caused by movement of material in Earth’s interior N S

  39. The Earth’s magnetic field produces a magnetosphere that deflects and traps particles from the solar wind protecting Earth

  40. Relevance of Earth’s protective magnetosphere • Protects against Solar Flares/CMEs- violent explosions on the Sun releasing large burst of charged particles into the solar system • Protects against Solar Wind - dangerous stream of charged particles constantly coming from the Sun • Northern Lights (Aurora Borealis)

  41. Northern Lights (Aurora Borealis) Charged particles from the Sun interact with the magnetic field around Earth. The particles collide with the nitrogen and oxygen atoms in the extreme upper atmosphere (ionosphere) and excite those atoms to emit light

  42. The Aurora • Caused when CME material reaches the Earth, it interacts with the Earth’s magnetic field, and collides with ionospheric particles

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