Examples of the last include the violet flash at sunset, the purple light of twilight, the indigo bands of a rainbow, or the face of New Moon during a total solar eclipse. All these are fantastically purple, yet the opportunities to see them are generally uncommon.
Even simultaneous color-contrast illusions combined with a nervous atmosphere can trick us into believing we can see the color purple in some stars. The 19th-century English astronomer William Henry Smyth was a master of simultaneous color-contrast perception. He noted, for example, that double star Eta (η) Cassiopeiae has a bright white primary with a lilac secondary.
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