Different Stars

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  1. Trespassers William - Different Stars | Releases | Discogs
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  3. Why are stars different colors?
  4. Why are stars different colors?

Our sky chart can help guide your eye.

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Trespassers William - Different Stars | Releases | Discogs

The colours of stars, however, are not obvious in most stars for several reasons discussed below. Colour is nonetheless an important and useful property of stars. In this page we will look at how it is defined, measured and used in astronomy. The photo above shows a small section of a starfield in Sagittarius taken by the HST from space.

The variety of colours of the stars is immediately obvious. Colours vary from bluish-white through to red. Why do stars have different colours? The colour of a star is primarily a function of its effective temperature. You should recall that a star approximates the behaviour of a black body radiator. As a black body gets hotter its colour changes. If you were to heat a solid shot put it would first emit radiation in the infrared region. Further heating would see it glow a dull reddish colour.

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With more heating it could eventually glow orange, yellow, white and eventually blue-hot. Ultimately if it were hot enough a black body emits most of its energy in the ultraviolet region. Although stars are not perfect black bodies this relationship between temperature and colour still applies to them. The colour that we see is usually an additive combination of the emissions from each wavelength. Hot stars appear blue because most energy is emitted in the bluer parts of the spectrum.

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There is little emission in the blue parts of the spectrum for cool stars - they appear red. Even though the Sun's peak emission wavelength Wien's Law corresponds to the green part of the spectrum, its colour appears pale yellow due to the relative contributions of the different parts of its Planck curve to the overall colour. The table below shows the approximate colour and temperature range for stars.

The colours shown in the above table are the correct hexadecimal codes for rgb monitors based on details from M. Charity at MIT. They represent the colour from an extended gas disk and not a point source. For more a detailed discussion visit his website. Even though stars have different colours, our perception of stellar colours in the night sky is poor.

The reasons for this are discussed next. Our eyes are extremely sensitive detectors of visible photons.

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Only a few incident photons are needed to trigger a stimulus response in our eyes. Why then do we not see star colours more readily? There are in fact several reasons:. Even if we use other detectors such as photographic plates or CCDs to detect light from stars rather than our eyes the colour recorded may not be the "true" colour of the star for other reasons. Interstellar space is not a perfect vacuum.

Cosmic dust is made up of small grains of silicates, iron, carbon, frozen water and ammonia ice 0. This means that light from a distant star is reduced in intensity so that the star appears dimmer than it would be if there were no intervening material. Termed extinction this effect can be estimated if the distance to the star and its position relative to galactic arms and molecular clouds is known.

In general more distant stars suffer greater extinction or reduction in brightness than nearby stars.

Why are stars different colors?

Extinction is inversely proportional to wavelength so red light is less affected than blue light. Distant stars thus appear more red than they actually are. This interstellar reddening must be compensated for in trying to determine the true colour and brightness of a star. If a star's spectral and luminosity classes are known its absolute magnitude and colour can be inferred.

By measuring its apparent colour the amount of reddening can be determined and this can then be used to determine an approximate distance to the star. Infrared and radio waves have even longer wavelengths than red visible light and can travel through the ISM relatively unimpeded hence they provide useful information about processes occurring within molecular clouds and galactic arms. Red giants such as Betelgeuse are not actually that red in colour. If you look at the colour in table 4. A small group of stars do, however, appear deep red. These are the carbon stars such as 19 or TX Piscium.

These ruby-red coloured stars have high abundances of carbon molecules such as C 2 , CH and CN in their outer layers that absorb most of the photons in the blue and violet parts of the spectrum. Carbon stars were traditionally classified as R and N classes with similar temperatures to K and M stars respectively. Nowadays they are collectively referred to as type C for Carbon.

When that happens, the star gets brighter and expands, and the star becomes a red giant. Main sequence white dwarf stars, like our sun, are in the central part of their evolution. In this phase, the helium in the core fuses into hydrogen.

Why are stars different colors?

These stars have a mass of 75 percent to percent the mass of our sun. Main sequence stars expand to become giant or super giant stars when the core hydrogen runs out. This progression, called solar evolution, varies greatly in time span. The higher the mass of the star, the shorter the evolutionary cycle, because higher-mass stars use their hydrogen fuel much more quickly than lower-mass stars.

This process can take as little as 2 million years for high-mass stars. Smaller-mass stars can last as long as 3 to 12 billion years, just about the same span of time as is projected for the galaxy.