Astro 18 – Section Week 2 EM Spectrum.

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Presentation transcript:

Astro 18 – Section Week 2 EM Spectrum

ElectroMagnetic Radiation Energy moves in waves with electrical and magnetic components All EMR travels at speed of light in a vacuum

ElectroMagnetic Radiation Energy = hν where v = c/λ h = 6.626068 × 10-34 m2 kg / s 21cm line (HI) has what frequency & energy? 1427583133.3 Hz Or 1.4276 GHz E= 9.4592×10-25 J

ElectroMagnetic Radiation

ElectroMagnetic Radiation

Wien’s Law Distribution of radiated energy from blackbody at T1 has same shape as distribution at T2 except it’s displaced on the graph λmax = b/T b= 2.8977685×10-3 m·K T = temp in Kelvin

Wien’s Law - Sun First need temperature of sun Total power radiated = 4*1026 Watts Radius = 7*108 meters Then, λmax= b/T b = 2.8977685×10-3 m·K

Wien’s Law - Sun

Wien’s Law - Student Body temp ~ 98°F Convert to Kelvin λmax = b/T b = 2.8977685×10-3 m·K So λmax = 10μm which is far-IR

Spectral Lines 2 Types: Emission Absorption

Emission Lines Cloud of gas, warmer than background

Emission Lines

Absorption Lines Hot source behind cloud of cold gas

Absorption Lines Useful in planetary atmospheres The deeper absorption line at 760nm is caused by our atmosphere's oxygen molecule. The two absorption lines at 720 and 890nm (from methane) appear on Saturn and Titan, but the rings do not have them

Doppler Shift Classic sound example: Because the source of the sound is moving towards/away from you

Doppler Shift Same thing occurs with light from stars, etc In H, the transition from level 2  1 has a rest wavelength of 121.6 nm. Suppose you see this line at a wavelength of 121.3 nm in star A and 122.9 nm in star B. Calculate each star’s speed and state if it’s moving towards or away from us.

Red Shift & Distance In general everything is moving away from us - expanding universe Red shift can be used to calculate distance to objects (Hubble’s Law)

Redshift & Distance For this galaxy, the measured wavelength of the Ca K line was 3962.0 Å, rest wavelength for Ca K is 3933.7 Å

Redshift & Distance NGC 1357

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