Introduction to Solar Observing	Course Overview	Course Syllabus	Course Schedule
		Index of Course Sessions

Diffraction

Diffraction occurs when light waves encounter a narrow opening and are bent around the edges of the opening, as illustrated in Figure 18. The opening must be comparable in size to the wavelengths of light for the effect to be noticeable.
Figure 18 Diffraction of light waves through a long, narrow slit. Courtesy of  The Center for Occupational Research and Development		Figure 19 Interference of  light diffracted by two long, narrow slits.
When two narrow openings exist near each other, interference with other transmitted waves will result. This effect is shown in Figure 19, as  monochromatic (one color) light encounters two narrow  adjacent slits. The diffracted light through the slits may travel different distances before meeting at the screen, so the crests of one set of light waves may not necessarily coincide with the crests of the other. Where crest and crest coincide on the screen, a region of brightness appears, and where a crest and trough coincide a region of darkness appears. The successive regions of brightness and darkness are called "interference fringes."

Diffraction and interference act together to produce a spectrum from a white light source as in Figure 20.	Figure 20 Diffraction grating spectrum.