S-1. Sunlight & Earth S-1B. Global Climate S-3.The Magnetic Sun
S-4. Colors of Sunlight Optional: Doppler Effect S-4A-1 Speed of
Light S-4A-2. Frequency Shift S-4A-3 Rotating Galaxies and Dark
Matter S-5.Waves & Photons Optional: Quantum Physics Q3. Energy
Levels Q4. Radiation from One widely used property of waves is
the shift in frequency when the source approaches or recedes. If
the engine of a train blows its whistle as it passes by, a
listener standing near the track cannot help but notice that the
tone of the whistle drops as it passes. Actually, the tone is
already raised above its normal note as the engine approaches,
and then drops below it as it recedes. This shift in frequency,
also noted in electromagnetic waves such as light or radio, is
named the Doppler Effect after its discoverer, the Austrian
Christian Doppler, born in 1803. Earlier, a somewhat similar
phenomenon was discovered by the Dane Ole Roemer in 1676. The
story deserves to be told because it also led to the first
determination of the