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 Observations: Seeing in visible wavelengths
Stars come in a variety of masses, with the vast majority containing between one tenth and ten times the mass of our Sun. The different masses determine how efficiently they generate energy and this gives rise to the surface temperature. Lower temperature stars shine with red light and high-temperature stars are blue or white. Being yellow, our Sun is a middle temperature star measuring around 6000°C.
The visible wavelengths are also the realm of the emission nebulae. They are glowing clouds of gas and often form some of the most breathtaking objects in the Universe, most often appearing red. This colour comes from the predominant emission from nebulae, which is hydrogen gas.
Because of the nature of the structure of the hydrogen atom, when it releases energy it does so efficiently at a specific wavelength of red light (656 nanometres).
The most common way for astronomers to analyse visible light from a celestial object is to split it into its constituent wavelengths to form a spectrum. Studying this allows astronomers to analyse the composition and physical condition of the celestial object under consideration.
If they are close to a star, dust clouds can reflect visible light. Such clouds usually create blue patches in space, similar to the colour of our daytime sky.
Last update: 5 November 2004
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