how does an astronomer determine the chemical identity of the gases in the stars atmosphere?

Question

how does an astronomer determine the chemical identity of the gases in the stars atmosphere?

Answer 1

Gene L. is exactly right. Expanding on this for those who may not know what a spectrometer looks like, it is the same as a prism here - it splits light into bands of color. However, elements emit unique patterns of thin lines in stead of a continuous band from violet to red. (it looks like a rainbow-colored barcode)

The "barcodes" for elements are as unique as fingerprints. Additionally, you may have heard of "red shift" and "blue shift." We all know the doppler effect when it comes to sound - a race car's engine changes tones as it zooms by. It goes from high pitched as the car approaches to low as it goes away.

Light does this too. Objects moving away from us look more red than they would sitting still relative to us, and those coming towards us look more blue. How can you tell what color a star is supposed to be, and why is it redder or bluer than that? The specrtra tell us. A barcode will be further to the left or right than it should be, and that shows the red / blue shift.

So that's a little more info about spectroscopy for those who're interested. ;)

Answer 2

By observing the spectra of light from the stars. Each element has a unique signature of colors that it emits when heated up hot enough to emit light (When it's a plasma). These are emission spectra. They appear as narrow stripes of different colors of light with dark areas in between them in the familiar "Rainbow" pattern of white light.

They also look at "Absorption Spectra" which are the opposite. A star's core emits all kinds of radiation including visible, UV, IR light, radio, microwaves, et al. The outer envelope of the star contains elements such as Hydrogen and Helium (Like our sun), which can absorb parts of this white light and leave holes in the spectrum, like the opposite of the emission specra above (Narrow black stripes missing from the rainbow). Helium was discovered this way on our own sun before it was discovered here on earth.

Answer 3

Zerobyte didn't mention that, to get the "light stripes" or the "bar code" the spectroscope has to have a very thin slit through which light passes. The stripes and bars are images of the slit, and discrete colors (wavelengths) that represent elements or ions in the atmosphere of the star pass through it (emission spectrum) or are blocked, allowing other wavelengths to pass (absorbtion spectrum). The image, of course, has to be focussed by lenses to be of use.

Answer 4

spectroscopy. basically breaking the stars light down into the spectrum. then they can see blanks in the spectrum where some material has absorbed radiation and areas that are brighter where some material has given off radiation.. each element has its own unique signature of these lines and so astronomers can tell what stars are made of this way.

Answer 5

By the color (light spectrum) that appears when the atmosphere is photographically recorded and analyzed..

For example, oxygen gives off different wavelengths of light than methane. Scientists hook up a spectrometer to a telescope to read which wavelengths of light the atmosphere of a planet is giving off.