Doppler Effect The Doppler Effect is the motion induced change in the observed frequency of a wave. The effect can only be observed/seen due to the relative motion between the observer and the wave source. A net motion towards the source causes a blueshift – a shift to higher frequencies - in the received beam. A net motion away from the source causes a redshift. The degree/ extent of the shift is directly proportional to the observer’s velocity relative to the source. http://webphysics.davidson.edu/Applets/Applets.html

Doppler again ?

Spectroscopy Recall - atom/molecule emits radiation in the form of photons. This radiation can be picked by a spectroscope, a device that disperses this radiation. Spectroscopes have diffraction gratings that act like prisms.

Spectroscopy 3 types of spectra: 1. continuous, 2. emission and 3. absorption. Kirchhoff’s Laws P. 89

Spectroscopy and Sources. 1. A luminous solid or liquid or a sufficiently dense gas. 2. Low density hot gas. 3. A cool thin gas absorbs certain wavelengths from a continuous spectrum.

Actual Spectra

Spectra from: The Sun: Numbers are in nanometers

Spectral Information Doppler effect and line broadening: when a familiar pattern of lines appears, but the lines are displaced from their usual locations. Thermal Broadening ->

Spectral Information Rotation Broadening.

Spectral Information Wien’s law: wavelength of peak emission ~ 1/Temperature. What this says is that the hotter the object the bluer its radiation and vice versa. Temperature is measured in Kelvins (K) where kelvins = degrees Celsius + 273 (page 73). Temperature is a direct measure of the amount of microscopic motion within an object: the hotter the object, that is the higher it’s temperature, the faster its constituent particles move and the more energy they radiate.

Summary of spectral information. Peak frequency or wavelength (continuous spectra only) Temperature (Wien’s law) Lines Composition, temperature Line width Temperature, turbulence, rotation speed, density, magnetic field Doppler shift Line-of-sight velocity