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.
If it's moving away from you it's wavelength will be increased. Since most objects in space that we study are moving and also emit light, we can tell if they're moving toward or away from us by measuring their wavelengths. There's an excellent animated demonstration of the doppler effect at this website ==>http://www.astro.ubc.ca/~scharein/app...