1. 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

2. Doppler again ?

3. 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.

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

5. 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.

6. Actual Spectra

7. Spectra from: The Sun: Numbers are in nanometers

8. 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 ->

9. Spectral Information • Rotation Broadening.

10. 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.

11. Summary of spectral information.