Gustav Kirchoff

SPECTRA

Gustav Kirchoff Three types of Spectra 1. Continuous Spectrum 2. Emission Spectrum 3. Absorption Spectrum

Radiation given off by luminous solids, liquids, and opaque gasses form a continuous spectrum Luminous Solid = Tungsten filament of an incandescent bulb Hot Liquid = Hot, moltant lava Opaque Gas = Gas you can’t see through

Radiation given off by transparent (thin or rarefied) excited gases form an emission spectrum (bright line spectrum) A transparent gas does not need to be hot to emit energy

The strength of a bright spectral line is determined by the peak size

When two or more gases are combined the relative intensities of the spectral lines tells us the relative quantity of the gasses. Formulas

0.0029   Wein’s Law  max is in meters, T is in Kelvin

2.9107    max in Angstroms, T is in Kelvin

 So as temp increases the maximum wavelength decreases.  Very useful in determining the temp of stars. Don’t need to know how far away or the size of a star Just need to know the dominant wavelength

How much Energy The total amount of energy radiated by a blackbody depends on its temp and surface area.

Total emitted Energy E = T4 E is in Joules per m2, T is in Kelvin  = 5.67x108 W m-2k-4

We see the stars by the light they emit due to their high temps We see the planets and moons by the light they reflect

What would be the surface temp of a protostar if it emits the greatest amount of energy at 30,000 Angstroms? RESULTS

The Sun’s continuous spectrum tells us that light must come from a hot solid, hot liquid, or hot dense opaque gas

The Sun’s yellowish color indicates a peak emission energy of about 5000 angstroms

The Sun’s dark lines in its spectrum indicates There must be a relatively cool gas above the photosphere The temp of the Sun’s surface is about 4500 K

The Sun’s Flash Spectrum The moon progressively eclipses the sun The photosphere becomes blocked Only the Sun’s atmosphere is visible The spectrum then changes from a dark line to a bright line Happens quickly – therefore called Flash Spectrum Since the emission lines appear pinkish the emitting region is called the chromosphere Above the chromosphere is the corona ~ 2 million K

Ionized Gas Between the Stars Nebulae – means cloud Radiates UV energy captured from massive “O” type stars The resulting ionized hydrogen gas is called H II regions H I regions are are non ionized hydrogen gas clouds