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Atmosphere

Atmosphere. ASTR 3010 Lecture 5 not from the Textbook. Seeing and scintillation. Atmospheric extinction. Three major components Rayleigh scattering : scattering by small particle Blue light gets scattered much more than red light  blue sky!. Atmospheric extinction.

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Atmosphere

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  1. Atmosphere ASTR 3010 Lecture 5 not from the Textbook

  2. Seeing and scintillation

  3. Atmospheric extinction • Three major components • Rayleigh scattering : scattering by small particle • Blue light gets scattered much more than red light  blue sky!

  4. Atmospheric extinction • Three major components • Mie scattering : scattering by larger particles • Wavelength independent  white cloud

  5. Atmospheric extinction • Three major components • molecular absorption Fraunhoffer lines

  6. Airmass Kasten and Young (1989) Airmass python program of calculating airmass for a given elevation.

  7. Airmass Calculation with Python from pylab import * from numpy import * … za = arange(0.0,90.0,0.1) airmass = 1.0 / (cos(radians(za)) + 0.50572*(96.07995 – za)**(-1.6364)) plot(za,airmass, ‘ro-’) xlim([80,90]) xlabel(‘Zenith Distance’) ylabel(‘Airmass’) show()

  8. Atmospheric window

  9. Atmospheric absorption bands

  10. Atmospheric absorption bands UBVRI Q M J K H L N Y near-IR Mid-IR • Optical bands : science driven (e.g., B and V to separate the Balmer Jump) • Near-IR and mid-IR bands : based on availability

  11. High mountains are best! 14,000 ft 45,000 ft

  12. and dry weather!

  13. and dry weather!

  14. and dry weather!

  15. Python Homework • Using data from http://www.gemini.edu/?q=node/10789 • Create a plot of atmospheric transmission for airmass=1.0 & 2.0 and PWV=1.0 & 5.0mm

  16. Effect of Dust • Gas manifest only in few allowed transitions (emission lines or absorption lines). It does not change the shape of the spectrum (unless they are optically thick!)!! • However, dust particles can change the shape of spectra • extinction (interstellar, telluric)  advantages of different wavelength astronomy • e.g., extinction toward the center of Galaxy • reddening (telluric airmass, e.g., twilight) • scattering

  17. Correcting Atmospheric Effects • How do we correct the effect from the atmosphere?

  18. Effect of Atmosphere in Photometry • Airmass (extinction) correction (measure a standard star over large airmass)

  19. Effect of Atmosphere in Spectroscopy • Telluric correction : division by a smooth spectrum standard star (WD or …)

  20. In summary… Important Concepts Important Terms Scintillation Airmass PWV Scattering (Rayleigh and Mie) Extinction • Atmospheric transmission • Effect of altitude and PWV • Photometric bands w.r.t. Atmospheric windows • Airmass • Removing the effect of atmosphere in photometry and spectroscopy • Chapter/sections covered in this lecture : Not from the textbook

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