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Stars Coloured Red by Interstellar Haze Tiny grains of dust in the interstellar medium scatter the blue portions of starlight coming our way from the far-away stars more than the red wavelengths. As a result, some blue light is “removed” from the light reaching us, so that distant objects appear redder than they actually are. This effect is known as the interstellar reddening of light, or “extinction”. This interplay between starlight and dust grains is particularly noticeable in the upper-left region of the Lagoon Nebula. There, the many stars look like dots painted in various hues of orange and red, peeking out through the veils of dust and gas between us, the observers, and the stars themselves. In contrast, the bright blue and white stars seen throughout the region indicate patches where little dust intervenes. Astronomers must take this reddening effect into account when analysing data obtained from such stars, especially in the visible part of the spectrum. The same mechanism takes place every time we find ourselves enjoying a beautifully coloured sunset. The scattering of sunlight by various particles in the Earth's atmosphere produces the Sun's intense red and orange hues.
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