How Astronomers Identify Elements in Stars Using Light Spectrum Analysis

hello everyone and welcome back my name is Mr kovalt and in this video we're going to talk about how we know what

elements are in in the stars and in order to talk about that we're needing we're going to need to talk about the

emission and absorption spectra of different elements so let's get into this

so how do we know which stars have which elements well we can analyze the wavelengths of

light that are absorbed or released by The Stars themselves and so what this means is that depending

on what elements are in a particular star different wavelengths of light are absorbed or released from the stars

and so if we can detect that and see which bands of light or which wavelengths of light are absorbed or

released by The Stars we can then indicate what elements must be in there to to uh

uh to give us that result okay so before we get into that we need to

talk about what's happening in the atom right what's happening in the atom when uh when you get this absorption or

release of energy and so uh we what we need to focus on are the electrons so when you put energy into the atoms of a

substance uh it's the electrons that are going to pick up some of that energy and so if you give the atom energy the

electrons can absorb that energy and then they're then they go up to a higher energy level so if you remember from a

previous video we talked about how the energy of the electron is associated with the energy levels that it's at and

so the uh the the electrons tend to be at lower Energies and they're going to be closer to the

nucleus so they're going to be down lower right but if they absorb some energy

then that's going to kick them up to a higher energy level they're going to then be farther away from the nucleus so

uh in the beginning we can see that this electron here is in its the lowest energy State possible so we call that

the ground state and so when we put the energy into the electron when the electron absorbs

energy it then jumps up to a higher energy level and we call that the excited state so think about an analogy

is like when you get excited that means that you have energy okay so the electron absorbs energy jumps up to a

higher energy State called the excited state ground state to excited state so this is very much like you climbing a

ladder right so again when you're closer to the ground you have a lower gravitational potential energy but as

you climb up to higher rungs on the ladder your gravitational potential energy increases same thing for the

electron so here we have a kind of potential energy for the electron in its ground state this is the lowest energy

when it absorbs energy it goes up to a higher energy State more potential energy

but electrons are not going to stay in that position very long right so again they don't want to be in a higher energy

State they they actually prefer to be in a lower energy state so what's going to happen is the electron is going to then

release that energy that it absorbed and go back down to the lower energy state it was so it's going to relax we say

this is relaxing so the excited electron relaxes back down to ground state in doing so it loses that energy so going

from a high energy to low energy it's got to lose that energy and it loses that energy often in the form of light

and so again it's following the alpha principle right the alpha principle says electrons want to be in the lower or

lowest energy possible so they're going to fall back down so again person on the ladder they might slip and fall and that

and as they fall they're going back down towards the ground losing gravitational potential energy so this is analogous

and so here you can see in this picture you've got energy level two and energy level one so the electron here went from

ground state here E1 is its ground state and it goes up to E2 higher energy level because it absorbed energy

and then it comes back down and when it does it releases a photon of light so remember particles of light we call

those photons and they have wavelengths and the the energy of the light we can figure that out by multiplying this

planks constant times the frequency of the light uh which is the inverse of the

wavelength and so here's the equation down here but the thing to keep in mind here is that the energy difference here

between the two energy levels is the same as the energy and the light that's being released so if you want to know

what energy levels or how big of a gap here you then measure the energy of the light and you'll know how much of a gap

between the energy levels the electron trans transition to through and so there's different ways to draw

this same picture so basically you want to make sure that you're showing If energy is coming in or out in which

direction the electron is moving right so here and you've got the Bohr model here and you've got two orbits and so in

this picture you have the electron moving from an inner orbit that is closer to the nucleus so this is low

energy because remember the closer you are to the nucleus the lower your potential energy so it's like being

close to the Earth right closer you are to the Earth the lower your gravitational potential energy but if

you uh go to a higher energy level this higher orbit which is farther from the nucleus so that indicates higher energy

so this electron here absorbs energy so there's the energy going in the electron jumps up to a higher energy state so it

gets excited and there it is at a higher energy State because it absorbed energy and then later on very soon afterwards

the electron is going to relax back down to the lower energy State and when it loses that energy it releases that

energy in the form of light so the light then has a certain amount of energy that energy of the light is equal to the Gap

that the electron moved between and so that's going to indicate a certain wavelength because wavelength

and and energy is really are related to each other and again we can use this picture here

for the same idea here we have a lower energy State here we have a higher energy State you can heat up the atoms

putting energy into the atoms and so the electrons will pick up some of that energy so they absorb the energy going

to a higher energy state which is now the excited state and then they relax back down to the lower energy State at

releasing light and again that light the energy of the light is going to have the same amount of energy that is the

difference between the two energy states and so that energy is going to be related to wavelength

okay so we can then you know um see the light that's emitted from these different substances so the amount

of energy that is given off by these substances uh well is going to depend on the energy levels that the electron is

falling from we just saw that so the the energy level how big of a gap there is it means that the

um the difference in energy is going to be larger and if the electron jumps from uh jumps a larger distance from a high

energy to low energy then the amount of then the light the photon of light emitted is going to have more energy and

therefore it's going to have a a a certain wavelength and so here we can see in this picture that the amount of

energy so we have high energy down here and we have low energy up here and you could see the wavelength changing so

high energy is associated with very short wavelengths and low energy is associated with longer

wavelengths so as we were talking about before the the larger the gap between the energy

levels that the electron is jumping between right so if the electron Falls from one energy level to a lower energy

level if that is a larger Gap that means the photon that's released is going to have more energy and if it has more

energy than the wavelength is going to be smaller if the Gap is smaller if the Gap that the electron is falling between

is smaller then that means the photon light Photon that's being released is going to have smaller energy and

therefore longer wavelength and so here in the middle you could see this visible

spectrum this is the spectrum of light that we can actually see anything beyond that Spectrum we can't see so UV light

uh pet scans gamma rays we can't see those those are invisible to us and even on this side when they're longer these

are invisible because our eyes can only pick up wavelengths within this small band here and the thing I want to point

out here is that you could see here that the color of light is in a certain order so red is on top Violet is on the bottom

and we'll talk about that in a moment so here we have different series of light and so the electron

can jump from any level to any level right so here we have this small inner one that would be your n equals one that

really tiny circle around the nucleus right so that's energy level number one and then this second one here is energy

level number two this third one here is energy level number three energy level number four energy level

number five and then we have six out here and seven so we have seven energy levels being represented here and the

electron can jump up to any one of these levels and fall back down to a lower level

so the electron can jump to this level fall back down to this level or it could jump up to this level fall back down to

this level so you could see that there's different uh ways in which the electron can go down to a lower level and as I

was saying before the larger the jump down by the electron the more energy that's

released right because you got a larger gap between the energy levels larger Gap means you know larger difference in

energy and so that means if the electron jumps from way up here down to here the energy is going to be is that's released

is more and so the photon of light that's released is going to have higher energy and therefore lower wavelength

you if you see down here the electron jumps from this energy level down to this energy level so it's got a smaller

Gap so the light that's released from that electron when it moves down to this lower energy level is going to be

smaller so small energy means longer wavelengths and so remember the wavelength of light is associated with a

particular color right so here in this series called the Balmer Series this is where we can see a visible light now

these other series The Lyman series and the pascan Series bracket series and so on

these series also produce light but a lot of the light that we see

is is not visible to us so much and much of the Rays much of the light that's being

released by these transitions are not visible to us but this series is visible to us

and so what happens when these electrons uh release the light well different elements have different

numbers of electrons and those electrons are filling in different energy levels and the thing we have to understand is

that as we put more electrons into a particular atom right of a particular element right

every time you put an electron into an atom into a different energy levels those that additional electron causes

the energy levels to change a little bit so no element no atom of a particular element is going to have the exact same

energy levels as another atom of a different element because different elements have different electrons and

the number of electrons kind causes the energy levels to change a little bit so when you look at what energy is being

absorbed or emitted by a particular element only that element will produce those

different waves of light those different wavelengths of light so this is like a fingerprint of an element so just like

we have fingerprints to identify different humans and every human has a different fingerprint so also the

elements have different emission spectrums they have different Atomic Spectra that identify that element and

only that element so hydrogen you could see these bands of Light by High hydrogen only hydrogen will give those

bands of light so these like the these are the bands of light or wavelengths of light that is emitted by hydrogen and

hydrogen alone so here we have all these bands of light from neon you can see that there's only a few bands of light

from hydrogen hydrogen only has one electron so there's not as many transitions by the electron from one

energy level to the other but neon has more electrons so there's many more transitions done by those electrons and

iron still has more bands of light because it has more electrons but none of these bands of light and iron are

going to be superimposed or match up with any of these bands in neon because the energy levels are different they're

they can be very close but they're going to be slightly different okay so the energy Spectrum so you can

measure the exact wavelength and when we get the light so we're going to get the light from the atoms we can then measure

the exact wavelength of the light and then that wavelength will tell us how big of an energy gap that electron fell

from right so we know that as the electron Falls from lower to from higher to lower it releases a a photon of light

with a wavelength and that wavelength is associated with the amount of energy lost by the electron which is associated

with how big that Gap is and so here we can see the rainbow of light

and as I was telling you before the order of the colors tells you the uh the uh energy so red has low energy purple

has high energy or indigo violet if you want to go that right way so low energy is associated with longer wavelengths

and high energy associated with shorter wavelengths so as you go from red to purple you are going from low to high

energy so purple light has higher energy than red light so that what that means is that when you put if you find a

purple light being emitted from an atom that means that the electron that that gave off that light was

uh relaxing or going through uh through a different Gap a larger Gap in its energy so it fell down a larger Gap and

produced a higher energy light so it lost more energy and produced uh that light if you see red light then the

electron only lost a little bit of energy because it jumped down to a lower energy that was not as big of a gap

between them and so you can see that with orange yellow green and blue so the easy way to remember the order of the

colors is by remembering Roy G Biv that's think of that as someone's name Roy is the first name g is the middle

initial and Biv is the last name so Roy red orange yellow G for green and then Biv is blue indigo violet here here they

have purple but indigo violet is often said as well so how do we get these uh emission

Spectra so there's two ways that you can get uh Spectra so uh wavelengths

um what wavelengths does it give off or which wavelengths does it absorb so either way is used so when we're looking

at emission Spectra the way this works is we're looking at a hot gas we're looking at the light that is absorbed or

given off by that hot gas so the light that's given off passes through a prism and then as the light passes through a

prism different wavelengths of light are separated from each other based upon how quickly they can go through this this

prism and different wavelengths of light can go uh more or less quickly through there and so you get the bending of the

light and they get separated here and so this is an example of emission spectrum so different light bands that are

produced get passed through this prism and then they get separated here so these are the emission this would be an

emission spectrum of whatever this hot gas is another way you can do it is through an absorption spectrum and the

way this is the opposite the way this works is you have a light source again and so this light source is producing

all of the wavelengths of light so all the wave all the different wavelengths of light are passing through this cold

gas now we have a cold gas this cold gas is now going to absorb certain wavelengths of light instead of emitting

them so most of the light is going to pass through this cold gas except for the ones that are absorbed by the gas

and so the light then passes through the prism and then you get this more color this this uh the spectrum of color and

what's going to be different here is that instead of having the bands of light show up you're going to have dark

spots show up where the bands of light should be and they don't show up because that light was absorbed by the gas

so either way we can identify what the element is either by what what

wavelengths were absorbed or what wavelengths were emitted and they are going to be the same wavelengths it's

just that one is showing you them as emitted and one is showing you them as absorbed

and so here's the example again so here's what you would see from natural light or from a light bulb so you have a

light bulb giving off all the wavelengths of light those wavelengths of light pass through the prism and you

get this rainbow this continuous Spectrum there's no gaps it's all rainbow all together that would be

normal the emission spectrum as I said you have the hot gas and the hot gas is emitting certain wavelengths of light

those certain wavelengths of light are passed through a prism and then they are separated and you can see the bands of

light show up here on the Spectrum you'll notice that most of it is dark because this hot gas is not emitting all

of the wavelengths of light it's only emitting a few and so only the light that is emitted is being shown up and so

this will be identified this will help identify what the element is so this is what happens when we do a lab

now here when we're looking at the sun here when we get an emission spectrum the light source that's emitting all the

wavelengths of light passes through a cold gas some of those wavelengths of light are going to be absorbed so the

same wavelengths of light that were emitted here are now going to be absorbed here and so the rest of the

light that passes through goes through the prism and then you can see that they are you can see the colors of light here

and then the ones that are missing are the exact ones that are emitted here but they're emit they're missing here

because the cold gas absorbed them so this is an absorption spectrum and this is what happens in the Stars right we so

normally we have absorption Spectrum so what about flame tests so we can do flame tests in a lab and we can say oh

from the flame test we can identify the different colors and different colors will identify uh different elements in

the substance and so here you can see that you got lithium chloride sodium chloride potassium chloride rubidium

chloride they're all chlorides but they're producing different colors so if it was the chloride that was producing

the color they should be all the same color but they don't have the same color so it must be the metal

ion here the first ion lithium sodium potassium those are the ions that are producing the color so here you can see

lithium producing reddish color here sodium is producing a bright yellow color

potassium sort of you know magenta color if you will calcium down here is producing a really bright orange color

and so on so you can identify what element there is by the color that you see because again different elements

produce different wavelengths of light and therefore different colors and so this is where your fireworks come in

different fireworks produce different colors because they have different elements mixed in with the uh the

firework itself so you if you see blue that means copper chloride was put in there or maybe it was copper some other

copper compound copper is a typical color that uh that a typical element that gives blue if you have sodium in

there then you would see a yellow color so yellow is indicative of sodium being in the firework calcium chloride we saw

calcium given orange color so if you see orange in your firework then that indicates that calcium was in in there

so this is why different fireworks give you different colors and you can get a mixture of colors because you have a

mixture of different elements in the fireworks and once again we can see here that we

have these different emission Spectra and these are the Fingerprints of different elements so just like we

humans have different fingerprints and we can be identified by our fingerprints each element has a different Spectrum

with different bands of light different wavelengths of light that show up and these Spectra will identify the element

coming from a particular Sun so we can identify what elements are in different Stars by analyzing the different

wavelengths that come in and if those wavelengths come line up with particular elements then we know that in that

particular sun or Star we have those elements and here again is an example of a

absorption Spectrum so same thing you can see here that you have a rainbow but instead of seeing bands of light you see

dark bands you see uh bands that have no light and that's because they were absorbed by the element and so in this

case we're looking for dark spots and if those dark spots line up where light should be for that particular element

then we identify that element as being hydrogen or helium you know depending on where we see those dark bands so again

here this is where the absorption is Korean and so we don't see the light because it's been absorbed by the

element in that star or sun and again here's the different uh bands of light this is different Spectra that

we see from different um stars here's the Spectrum from the Beetlejuice yes there is a star called

Beetlejuice and so you can see the bands of light uh and you can see the dark bands where there is no light so you can

identify what elements are in that star here rigel this is the another uh absorption Spectrum for that star and so

we can use these to identify what what elements are there and so that's it for this video I hope

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