Dividing Light Into a Spectrum Astronomers separate out light into its individual components using a diffraction grating or using a prism - then they analyze each part independently!

Filter Detector 81 blue460 nm81

Filter Detector 85 blue460 nm81 green530 nm85

Filter Detector 83 blue460 nm81 green530 nm85 yellow580 nm83

Filter Detector 78 blue460 nm81 green530 nm85 yellow580 nm83 orange610 nm78

Filter Detector 70 blue460 nm81 green530 nm85 yellow580 nm83 orange610 nm78 red660 nm70 The spectrum is continuous. UVIR

Natural Spectra ????

Änuenue (rainbow) Water droplet Light from the Sun

Shine Light through Hydrogen…

Shine Light through Hydrogen…

E = h = hc/    = hc/EE = h = hc/ E = h h =Planck’s constant; =frequency [Hz=1/s]; =wavelength [m]  m  =  m=10 -6 m  E  eV  1.24 [  m eV]

 3  2  = = 1.89 eV

 3  2  = ~  m  m  =  m=10 -6 m  E  eV  1.24 [  m eV]

Shine Light through Hydrogen…

Thermal Radiation

Rules for Emission by Opaque Objects 1.Hotter objects emit more total radiation per unit surface area.  Stephan-Boltzmann Law: E =  T 4  5.7 x   [Watt/m 2 Kelvin 4  2.Hotter objects emit bluer photons (with a higher average energy.)  Wien Law: max = 2.9 x 10 6 / T (K) [nm]

Rules for Emission by Opaque Objects 1.Hotter objects emit more total radiation per unit surface area.  Stephan-Boltzmann Law: E =  T 4  5.7 x   [Watt/m 2 Kelvin 4  2.Hotter objects emit bluer photons (with a higher average energy.)  Wien Law: max = 2.9 x 10 6 / T (K) [nm]

Two kinds of Spectra: 1) Absorption If light shines through a gas, each element will absorb those photons whose colors match their electron energy levels. The resulting absorption line spectrum has all colors minus those that were absorbed. We can determine which elements are present in an object by identifying emission & absorption lines.

2) Emission Spectra The atoms of each element have their own distinctive set of electron energy levels. Each element emits its own pattern of colors, like fingerprints. If it is a hot gas, we see only these colors, called an emission line spectrum.

Lets look at continuous, absorption line, and emission line spectra –

Kirchhoff’s Laws I. A hot, dense glowing object (solid or gas) emits a continuous spectrum.

Kirchhoff’s Laws II. A hot, low density gas emits light of only certain wavelengths -- an emission line spectrum.

Kirchhoff’s Laws III. When light having a continuous spectrum passes through a cool gas, dark lines appear in the continuous spectrum – an absorption line spectrum.

Kirchhoff’s Laws IIII II

Telescopes

Astronomical objects emit all of these different kinds of radiation in varying amounts

Mm/Submm

Maunakea’s height

Radio wavelength observations are possible from Earth’s surface