Light, Color, Filters, Seeing, and Transparency

All light is composed of traveling electromagnetic waves. The human eye can see only visible light. Non-visible wavelengths of light include radio waves, microwaves, infrared radiation, ultraviolet light, X-rays, and gamma rays. Light can undergo bending processes known as refraction and diffraction. Black body curves display the intensity of light at different frequencies emitted by objects at different temperatures. These curves are used to estimate the temperature of stars. Light can also be Doppler shifted if a light source is moving toward or away from an observer. The amount of the Doppler shift is directly related to the line-of-sight velocity of the source relative to the observer. Spectroscopy is the study of the interaction of light with matter. Matter can emit or absorb light at specific wavelengths characteristic of the atoms or molecules present. Spectroscopy can be used to identify the composition of celestial objects. Ground-based astronomical studies are limited by the transparency of the atmosphere and the astronomical seeing (a measure of the amount of atmospheric turbulence along the line of sight).