1. Atmosphere ASTR 3010 Lecture 5 not from the Textbook

2. Seeing and scintillation

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

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

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

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

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. N J K H Q L M Y near-IRMid-IR UBVRI 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!

15. Python Homework Using data from http://www.gemini.edu/?q=node/10789 Using data from http://www.gemini.edu/?q=node/10789http://www.gemini.edu/?q=node/10789 Create a plot of atmospheric transmission for airmass=1.0 & 2.0 and PWV=1.0 & 5.0mm 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!)!! 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 o extinction (interstellar, telluric)  advantages of different wavelength astronomy  e.g., extinction toward the center of Galaxy o reddening (telluric  airmass, e.g., twilight) o scattering

17. Correcting Atmospheric Effects How do we correct the effect from the atmosphere? 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) 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 …) Telluric correction : division by a smooth spectrum standard star (WD or …)

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