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By looking at the lines in a star's spectrum of light, astronomers can tell what kinds of elements the star is made of. This happens because when a beam of light hits an atom or molecule, that atom absorbs a characteristic wavelength (color) of visible light. Scientists have made a huge list of different elements and the different patterns of lines observed in theirj corresponding "spectra" (fancy word for light spectrums), and by using such lists can deduce precisely what each star is made of.
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MaxineMany stars produce close to or near a full continuous spectra. However, many of the stars observed on Earth, are at a large distance away. This means, that the direct path from the distant star to Earth, most likely lays gas clouds and other stellar objects. Gas clouds absorb certain wavelengths emitted by the stars, and convert this energy into other forms like heat. This basically removes spectral lines from the previous continuous spectra, to where, we on Earth, observe an Absorption spectra.
Its composition (how much of each element is there in the visible part), and - through the Doppler effect - its speed (whether it is coming towards us or moving away from us, and how fast). It can also give a rough idea how fast the star is rotating - through the same Doppler effect.
The absorption spectrum depends on the chemical composition of the star. For two stars to have exactly the same spectrum, they would have to have exactly the same elements in the same ratio. Also, since the light is color-shifted by the Doppler effect, it means they'd not only have to be identical in composition but would have to be approaching or receding from us at exactly the same rate. The combination makes it very unlikely that any two stars will have precisely the same spectrum.
Absorption spectrums can identify a stars composition by studying the wavelengths of light that get absorbed by the cool gas atmosphere of the star, and different absorption specturms have individual characteristics that scientists can relate to the specific composition of any star.
You're looking at the "black lines",
those frequencies which have been absorbed by the intervening gases.
Ideally you start with white light, but in astronomy you take what you can get.
Note: each molecule has it's own absorption frequencies -
thus you can use an absorption spectrum to identify translucent substances.
The spectrum indicates the chemical composition of each star. As the chemical composition changes, the spectrum changes. However, because of the huge mass of stars, these changes are so slow they are not being "observed" by human astronomers. The relative velocity between each star and us is responsible for a shift of the whole spectrum. If a star is "approaching us", the spectrum is shifted towards the blue part of the spectrum. If the star "moves away" the spectrum is redshift.
A star's spectrum can tell you what elements the star is made out of, the temperature of the star, how/if a star is moving, the density of the star and much, much more. The color of stars are classified into 7 spectral types where O (blue) stars are the hottest and M and K (red) stars are the coolest.
This is a result of quantum mechanics: electrons are bound to atoms at only specific energy states. In other words, atoms will absorb photons of only specific energies, that correspond to the amounts of energy needed to excite one of its electrons to a higher energy state. As a result, specific colors of light are absorbed by different elements, and we can tell the composition of a hot gas by the spectrum of absorption and emission lines.
(Conversely, an electron decaying to a lower energy state will radiate a photon; this is, for example, why sodium streetlights are orange, for example. That same transition, know as the sodium D line, is seen in the solar spectrum, so we know the Sun contains sodium, and we can even find the relative amount of sodium in comparion to the other elements composing the sun.)
As for why the Sun's (and most other stars' ) spectrum is primarily absorption (dark) lines, and not emission (bright) lines...well, you would think that since the Sun is so hot, it would be glowing with emission lines, right? The explanation is surprising: It depends on the probability of a photon of a given energy being able to escape from a given depth into the Sun. Photons of just the right energy to excite an electronic transition in one of the atoms they encounter will get absorbed, while ones of the wrong energies will just get scattered off of any atoms they encounter, and continue to escape from the Sun. In other words, it's really hard for light at the specific energies corresponding to the absorption lines to escape form the Sun, so when you look at photons at those lines, you are able to see only a little depth into the sun, compared to most of the light you are seeing. The temperature of the sun increases with depth, so light that originated closer to the 'surface' is coming from a coolerregion, and so it is dimmer---the dark absorption lines! We call the photosphere the region of the sun where most of the Sun's visible light is last scattered, while the chromosphere, above the photosphere, is a layer of cooler gas that absorbs back some energies of ligh and gives the Sun its caharacteristic spectrum. Each statr has a unique spectrum, determined by its temperature and chemical composition (and some other minor things like its density, strength of magnetic fields, veclovity despersion of gas in the photosphere due to convection, etc.) Anyway, the main factor is the temperature; if we heated the Sun up or cooled it down, its pattern of dark absorption lines would change. This is how we determine the temperatures and chemical compositions of stars.
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What are the Dark lines that appear in a spectrum of light from a star called?
The dark lines that appear in a spectrum of light from a star are called absorption lines. These lines are caused by the absorption of specific wavelengths of light by elements in the outer atmosphere of the star. Absorption lines help astronomers identify the chemical composition of stars and other celestial objects.
Fraunhofer lines in the solar spectrum are actually?
Fraunhofer lines are dark absorption lines in the solar spectrum caused by specific elements absorbing certain wavelengths of light. These lines help astronomers identify the chemical composition of the Sun and other stars because each element absorbs light at characteristic wavelengths, leaving dark lines in the spectrum.
How do astronomers know that hydrogen is present in almost every star in the universe?
Astronomers use spectroscopy to analyze the light emitted by stars. By studying the absorption lines in a star's spectrum, astronomers can identify the elements present in its composition. Since hydrogen leaves a distinct signature in these absorption lines, scientists have found that hydrogen is the most abundant element in stars, including our Sun.
Is it true that scientists can learn about the chemical composition of stars by analyzing the light they transmit?
Yes, scientists can analyze the light emitted by stars, known as stellar spectra, to learn about their chemical composition. By studying the absorption and emission lines in the spectrum, scientists can identify the elements present in the star and their relative abundances. This information helps astronomers understand the processes happening within stars and how they evolve over time.
How do astronomers determine the chemical compositions of stars?
Astronomers determine the chemical compositions of stars by analyzing their spectra, which is the light they emit split into different wavelengths. By studying the absorption lines in a star's spectrum, astronomers can identify the elements present in the star's atmosphere. Comparing these absorption lines to known spectral lines of elements allows astronomers to determine the chemical composition of stars.
