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Atmosphere ASTR 3010 Lecture 5 not from the Textbook

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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. - PowerPoint PPT Presentation

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Page 1: Atmosphere

Atmosphere

ASTR 3010

Lecture 5

not from the Textbook

Page 2: Atmosphere

Seeing and scintillation

Page 3: Atmosphere

Atmospheric extinction• Three major componentso Rayleigh scattering : scattering by small particle

o Blue light gets scattered much more than red light blue sky!

I ∝ I01λ4

Page 4: Atmosphere

Atmospheric extinction• Three major componentso Mie scattering : scattering by larger particles

o Wavelength independent white cloud

Page 5: Atmosphere

Atmospheric extinction• Three major componentso molecular absorption Fraunhoffer lines

Page 6: Atmosphere

Airmass

Airmass python program of calculating airmass for a given elevation.

Kasten and Young (1989)

Page 7: Atmosphere

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()

Page 8: Atmosphere

Atmospheric window

Page 9: Atmosphere

Atmospheric absorption bands

Page 10: Atmosphere

Atmospheric absorption bands

NJ KH QL MY

near-IR Mid-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

Page 11: Atmosphere

High mountains are best!14,000 ft

45,000 ft

Page 12: Atmosphere

and dry weather!

Page 13: Atmosphere

and dry weather!

Page 14: Atmosphere

and dry weather!

Page 15: Atmosphere

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

Page 16: Atmosphere

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 spectrao extinction (interstellar,

telluric) advantages of different wavelength astronomy e.g., extinction toward

the center of Galaxyo reddening (telluric

airmass, e.g., twilight)o scattering

Page 17: Atmosphere

Correcting Atmospheric Effects

• How do we correct the effect from the atmosphere?

Page 18: Atmosphere

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

Page 19: Atmosphere

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

Page 20: Atmosphere

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