TRUE AND FALSE COLOR IMAGES
The beautiful photographs of nebulas, galaxies, and star clusters that appear in astronomy books and magazines often exhibit a riot of color: hot pinks, lime greens, deep reds, and neon blues.
As striking as they'are, they usually do not represent the object's true colors. Astronomers generate computer-colored images, purposely assigning colors to different levels of intensity so as to bring out subtle details. Images taken at radio and optical, wavelengths can also be represented by different colors and superimposed to form a composite. Such composites are helpful in correlating radio hot spots to optical sources.
False-color images are often used to map temperature differences and radiation intensity across an object. For example, both these close-up images of Halley's Comet are optical photographs' taken by the Giotto spaceprobe in 1986. While the top image uses-natural colors, the bottom image is computer processed to enhance relative brightnesses. The most brilliant part of the comet is coded white, with other bright regions in pale colors. The dark shades of'pink, orange, yellow, blue, and green indicate successively fainter areas of the comet.