Wavelengths of light outside our solar system

Question

The question might have been asked before. Our Sun's rays decompose into 7 elementary colors by using a prism or spectrometry. Can the the colors (their number and wave length in the spectrum ) be found by any other means of observation or instrumented measurement?

Are any stars outside the solar system in the universe known which have more or less than 7 colors and their spectral wavelengths ? Are they also known to have some electromagnetic properties?

Answer 1

I can measure the wavelength spectra of light using a variety of instruments:

1. A grating
2. A prism
3. thin-film filters
4. Fourier Transform Infra-red (MIchaelson interferometer) FTIR

are a few. The above list are the basic components upon which spectroscopy is built on, and there instruments come in a vast array of variations.

To address your last question, light from a star comes in 2 basic categories:

1. Black body radiation which is a result of a body having a temperature and being in thermal equilibrium
2. Some atomic or chemical transition. These tend to be narrow lines of spectra. The most common element to look at is Hydrogen.

Note, that your question appears directed at visible light (0.4 - 0.8 um), but there is a lot of other wavelength regions in the IR to look at.

Answer 2

The myth of the seven colors from the rainbow is due to Isaac Newton. While he discovered that the colors from sunlight can be decomposed using a prism, he thought there were six, then seven distinct colors. He associated it to superstitions about the number seven, to the 7 musical notes, and probably to some religious beliefs.

Colors can be defined, essentially, in two manners.

1. Physics say that there is a "line" of colors that we can see, from red to blue, with infinitely many colors in between. And there are actually colors before red (infrared) and after blue (ultraviolet), that we cannot see. You can also combine many colors from this "line", and to make white, you need all the colors together.
2. Our eyes (for most humans) have 3 different detectors, associated to three primary colors, red, green, and blue. All colors we see are a combination of those. Other animals may have a different number of color detectors. But for humans, you must mix red blue and green light to make white-looking light.

To answer your original question, the Sun does not emit 7 colors only, but all visible colors (almost equally). Other stars do the same, but sometimes with different proportions. They can be stronger towards the red or the blue end of the spectrum.

Answer 3

The seven elementary colors are a cultural convention. More scientific models of color vision use three. A prism can divide the spectrum much more finely. The best grating spectroscopes in astronomy divide the light from a star into hundreds of thousands of colors.