so its color is usually more or less the color of a black body. The color of a black body lies on the Planckian locus in the middle of the diagram shown here. As can be seen, this locus happens to pass through red, orange, yellow, white, and light blue areas, and one can indeed see many stars of these colors. On the other hand, it does not pass through green, indigo (dark blue) or violet areas, so stars that appear to have these colors are rare and depend on some additional optical effect. The (black body) colors of stars are sometimes confused with the colors of the spectrum. The spectral (rainbow) colors are those on the curved part of the boundary of the diagram on the right. As can be seen, the red, orange, yellow and blue rainbow colors happen to be much the same as black body colors, which range from pale cyan, to white, to yellow, to orange. However, stars whose peak emission is green light (around 6000K, similar to the Sun) also emit a great deal of both red and blue light, and the human visual system interprets this mixture of colors as whitish rather than green. So the fact that some spectral colors appear as star colors is more a quirk of human color vision than a property of stars: If one uses an instrument such as a spectroscope that is better at distinguishing wavelengths of light, then the separated spectral colors look different from the composite colors of stars. All sufficiently hot stars look about the same shade of blue (and not violet as claimed in some popular accounts). The reason for this is that at sufficiently large temperatures (above about 20,000 K) all black body spectra look about the same in visible light, though they can differ a lot at shorter wavelengths. Although their maximum output at visible wavelengths is at violet, they put out enough light at other wavelengths to look light blue: The color at the end of the Planckian locus rather than the color at the end of the spectrum. Objects that resemble green stars Although there are no truly green stars, there are many astronomical objects that can sometimes appear to be green stars. This section lists some of them. Beta Librae The star Beta Librae (Zubeneschamali, Lib) is usually described as appearing white to modern observers, viewed through