1 Many people find that boxes with a 1.25 or 1 1/8 hole restrictor on them before an egg is laid are not utilized, even by smaller birds like titmice and chickadees. 2  If the entrance hole is enlarged (e.g., by woodpeckers or chewing rodents), put a hole reducer on it.
The Doppler effect widens the spectral lines of rotating objects because the wavelengths changes from blue or red. Blue-shifted, red-shifted, and non-shifted photons mix together to get how its rotating.
The Doppler Effect. The Doppler effect was named after Christian Doppler, who first came up with the idea in 1842. He learned that sound waves would have a higher frequency if the source was moving toward the observer and a lower freqency if the source was moving away from the observer. A commonly used example of the Doppler effect is a train. When a train is approaching, the whistle has a higher pitch than normal. You can hear the change in pitch as the train passes. The same is true with sirens on police cars and the engines of race cars.