How do astronomers know which element is present where?

Answer 1

Emission spectra is used in the study of stars because when the lines emitted are studied, scientists are able to determine what the star is composed of. The temperature and mass of the star are also determined by the emission spectra.

Answer 2

The color spectrum can help astronomers tell if the star is moving closer or away from the earth by using dopler effect. If the color is shifted to the red part of the specturm (over the course of many observations) it means it is moving away. If the color is shifted to the blue or violet part it is moving closer. The same thing happens when you hear a siren go by; as it gets closer it gets louder than fades away the further away get gets. The color spectrum call also tell the astronomer what elements are present in the star. Each element has a unique color signture like a fingerprint. For the purposes of my answer, I will assume that you mean the spectrum of the light that the particular star under consideration is emitting. The spectrum of the starlight is separated into its different colors, or wavelengths, with a spectrometer, which uses a prism or diffraction grating to refract (or diffract) the light into different directions depending on the wavelength. You use photographic film or electronic detectors to measure the intensity of the light at each wavelength.

Recognize that the measured spectrum extends far beyond the visible colors which our eyes can detect. The visible spectrum is typically defined as covering wavelengths from 400 nanometers (blue) to 700 nm (red). Wavelengths shorter than 400 nm are the ultraviolet (then the extreme ultraviolet, then soft X-rays, 'regular' X-rays, etc.) Wavelengths longer than 700 nm are the infrared (then the far infrared, then microwaves, etc.)

A second important aspect of the star's spectrum that you need to know is the spectral shape, which is the graph of energy density vs. wavelength. A good illustration of this is shown on http://en.wikipedia.org/wiki/Planck%27s_law

There are several ways that the spectrum can be used. First off, if you look at the Wikipedia illustration, you see that the spectrum has a different shape for different temperatures. This allows you to tell what the surface temperature of the star is, which can give a good indication of the type of star (white dwarf, red giant, etc).

Second, if you look closely at the spectrum, you see there are wavelength that are very dim or missing entirely. They are very dim because that wavelength is absorbed by a particular atom in the star's outer atmosphere. (Or by dust and molecules that are between us and the star.) Every atom has its own set of wavelengths that it absorbs, so the set of absorption lines (as they are called) lets you figure out what atoms are present in the outer atmosphere. Hydrogen and helium are common. When you start seeing heavier materials, like carbon, sodium or silicon, then you know the star is old and nearing the end of its life.

Third, you can tell how far away the star is from the earth. Because the universe is expanding, all the stars (except a few that are close to us) are moving away from us. The further away they are, the faster they are moving away. This is known as "Hubble's Law", after Edwin Hubble who published it in 1929. (For more on this, see the Wikipedia article at http://en.wikipedia.org/wiki/Hubble%27s_law.)

One of the results of Einstein's theory of (Special) Relativity is that an object that emits light and is moving away from you looks redder (longer wavelengths) than the same object would if it were not moving. (This is called the Doppler shift, or red shift.) The amount of the shift depends upon the speed at which the object is moving. Once you have measured the spectrum, you can determine how much the spectrum is red-shifted, which tells you how fast the star is moving, which in turn tells how far away the star is.

-Dr.RSJameson 26-Feb-2008

Answer 3

The absorption lines in a star's spectrum tell us many things about the star, including its chemical composition (from which lines appear) and its speed toward or away from us (from the Doppler shift of those lines).

Answer 4

The emission spectra can tell us the atoms of a star and the atoms tell us what the star is made of

Answer 5

By studying the lines on the spectrum emitted by a star, scientists can determine what elements a star is composed of.

Answer 6

For this purpose, astronomers would analyze the starlight's spectrum.

Answer 7

Each element leaves a characteristic "signature" in the spectrum - lines at certain places of the spectrum indicate a certain element.

Answer 8

through a stereoscopy

Answer 9

yes