A casual look around the sky will reveal that not all the stars are of the same colour. Antares and Betelgeuse, for instance, are orange-red while Altair and Vega appear white or bluish-white. Colour is directly related to a star's surface temperature and the wavelength of the light emitted. Blue or white stars are hotter than those displaying an orange or red hue. Binoculars show the colours well, particularly where the components of a double star present contrasting shades. Examples include 8 Tauri, a prominent yellow and white pair in the Hyades cluster, and the superb gold, blue and green triple o1 Cygni. Conversely, fainter stars on the threshold of visibility appear white because they emit insufficient light to stimulate the colour receptors in the eye.
Occasionally, observers may encounter unusual stellar colours such as violet or mauve. These curious hues are sometimes caused by a phenomenon known as "dazzle tint", where a bright primary imparts false colour to its fainter companion. Star colours are naturally subjective, with opinions often varying between experienced observers. This is just one of the intriguing aspects connected with the study of double stars.
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