Astronomy - spectroscopy - 1/3

>> female narrator: The
>> female narrator: The
>> female narrator: The following is part of a college
following is part of a college
following is part of a college course based on the textbook
course based on the textbook
course based on the textbook Horizons: Exploring the
Horizons: Exploring the
Horizons: Exploring the Universe written by Michael
Universe written by Michael
Universe written by Michael Seeds and published by Thomson
Seeds and published by Thomson
Seeds and published by Thomson Brooks/Cole Publishers.
[dramatic music]
[dramatic music]
[dramatic music] ś ś
The universe is beautiful.
The universe is beautiful.
The universe is beautiful. Thousands of eyes look into the
Thousands of eyes look into the
Thousands of eyes look into the sky every night to catch a
sky every night to catch a
sky every night to catch a glimpse of the wonders that it
glimpse of the wonders that it
glimpse of the wonders that it paints with light, but this
paints with light, but this
paints with light, but this light does more than create
light does more than create
light does more than create amazing vistas; it can tell
amazing vistas; it can tell
amazing vistas; it can tell about the nature of our
about the nature of our
about the nature of our universe.
universe.
universe. Using the process of
Using the process of
Using the process of spectroscopy, in which the
spectroscopy, in which the
spectroscopy, in which the colors, mixed in a beam of
colors, mixed in a beam of
colors, mixed in a beam of light, are separated and
light, are separated and
light, are separated and analyzed, astronomers can
analyzed, astronomers can
analyzed, astronomers can uncover the secrets of the
uncover the secrets of the
uncover the secrets of the myriad sources of light that
myriad sources of light that
myriad sources of light that their telescopes can capture.
their telescopes can capture.
their telescopes can capture. Without the subtle data carried
Without the subtle data carried
Without the subtle data carried by the light, our understanding
by the light, our understanding
by the light, our understanding of the universe would be limited
of the universe would be limited
of the universe would be limited to only the beautiful images it
to only the beautiful images it
to only the beautiful images it creates.
creates.
>> Spectroscopy, I believe, is creates.
>> Spectroscopy, I believe, is creates.
the most fascinating part ofis creates.
the most fascinating part ofis creates.
modern astronomy, because itis creates.
modern astronomy, because itis creates.
enables you to tell somethings creates.
enables you to tell somethings creates.
about the nature of the objects creates.
about the nature of the objects creates.
in the universe in much details creates.
creates.
without going there and touching

them.

Because with spectroscopy, you
Because with spectroscopy, you
Because with spectroscopy, you can tell how hot a star is, how
can tell how hot a star is, how
can tell how hot a star is, how big it is, what mass it has,
big it is, what mass it has,
big it is, what mass it has, what the chemical composition
what the chemical composition
what the chemical composition is, and you can even tell how
is, and you can even tell how
is, and you can even tell how far it is away from us.
far it is away from us.
far it is away from us. And all the information comes
And all the information comes
And all the information comes from spectral lines in the
from spectral lines in the
from spectral lines in the spectrum of stars.
spectrum of stars.
>> narrator: Deciphering spectrum of stars.
>> narrator: Deciphering spectrum of stars.
mysteries of the universe with spectrum of stars.
mysteries of the universe with spectrum of stars.
spectroscopy requires a basich spectrum of stars.
spectroscopy requires a basich spectrum of stars.
knowledge of how light isasich spectrum of stars.
knowledge of how light isasich spectrum of stars.
created and how it interactsch spectrum of stars.
created and how it interactsch spectrum of stars.
with different types of matter spectrum of stars.
spectrum of stars.
to generate unique spectra.
To unlock the secrets of the
To unlock the secrets of the
To unlock the secrets of the infinitely large, we must
infinitely large, we must
infinitely large, we must start with an understanding of
start with an understanding of
start with an understanding of the infinitesimally small:
the infinitesimally small:
the infinitesimally small: the atom.
the atom.
In this model, the atom has two the atom.
In this model, the atom has two the atom.
major components: the first iso the atom.
major components: the first iso the atom.
theonucleus,ethe central core of the atom.
theonucleus,ethe central core of the atom.
the atom which is composed of of the atom.
the atom which is composed of of the atom.
tprotons,wwhich are positivelyof the atom.
tprotons,wwhich are positivelyof the atom.
charged, andineutrons,swhich are the atom.
the atom.
neutral..

The second component is the

cloud of negatively charged

electrons which surrounds the

nucleus.

The number of protons in the
The number of protons in the
The number of protons in the nucleus of the atom determines
nucleus of the atom determines
nucleus of the atom determines what chemical element it is.
what chemical element it is.
what chemical element it is. Hydrogen has one proton.
Hydrogen has one proton.
Hydrogen has one proton. Carbon has six protons.
Carbon has six protons.
Carbon has six protons. Neon has ten and so on.
Neon has ten and so on.
An electron can orbit the Neon has ten and so on.
An electron can orbit the Neon has ten and so on.
nucleus of an atom only at Neon has ten and so on.
nucleus of an atom only at Neon has ten and so on.
specific distances known as Neon has ten and so on.
specific distances known as Neon has ten and so on.
spermitted orbits. known as Neon has ten and so on.
spermitted orbits. known as Neon has ten and so on.
The number of protons in the Neon has ten and so on.
The number of protons in the Neon has ten and so on.
nucleus determines thein the Neon has ten and so on.
Neon has ten and so on.
arrangement of these orbits.

Here we have an illustration of
Here we have an illustration of
Here we have an illustration of an atom of hydrogen, one of
an atom of hydrogen, one of
an atom of hydrogen, one of carbon, and another of neon.
carbon, and another of neon.
carbon, and another of neon. The combination of orbits is
The combination of orbits is
The combination of orbits is unique to each element and can
unique to each element and can
unique to each element and can be used to identify them, much
be used to identify them, much
be used to identify them, much like fingerprints identify
like fingerprints identify
like fingerprints identify individual humans.
individual humans.
No two elements have the same individual humans.
No two elements have the same individual humans.
combination of permitted orbits. individual humans.
combination of permitted orbits. individual humans.
>> There is a very simple model. individual humans.
>> There is a very simple model. individual humans.
of the atom that was created by. individual humans.
of the atom that was created by. individual humans.
Niels Bohr. that was created by. individual humans.
Niels Bohr. that was created by. individual humans.
Niels Bohr. that was created by. individual humans. It's a model, but it is useful
It's a model, but it is useful
It's a model, but it is useful in explaining certain phenomena
in explaining certain phenomena
in explaining certain phenomena with regards to how light
with regards to how light
with regards to how light interacts with matter.
interacts with matter.
interacts with matter. It's not very realistic in other
It's not very realistic in other
It's not very realistic in other regimes, but it's useful in this
regimes, but it's useful in this
regimes, but it's useful in this application.
application.
application. You can imagine the electron as
You can imagine the electron as
You can imagine the electron as orbiting its nucleus.
orbiting its nucleus.
orbiting its nucleus. But the difference between an
But the difference between an
But the difference between an electron orbiting an atom, or
electron orbiting an atom, or
electron orbiting an atom, or the nucleus of an atom, and a
the nucleus of an atom, and a
the nucleus of an atom, and a planet orbiting the Sun, for
planet orbiting the Sun, for
planet orbiting the Sun, for instance, is that an electron
instance, is that an electron
instance, is that an electron cannot take on any orbit it
cannot take on any orbit it
cannot take on any orbit it wants.
wants.
wants. It is only allowed very specific
It is only allowed very specific
It is only allowed very specific orbits.
orbits.
orbits. >> narrator: Let's consider the
>> narrator: Let's consider the
>> narrator: Let's consider the simplest atom: hydrogen, which
simplest atom: hydrogen, which
simplest atom: hydrogen, which has just one proton and one
has just one proton and one
has just one proton and one electron.
electron.
electron. Although the electron can only
Although the electron can only
Although the electron can only reside in one of the permitted
reside in one of the permitted
reside in one of the permitted orbits at a time, it is free to
orbits at a time, it is free to
orbits at a time, it is free to jump between them.
jump between them.
jump between them. To understand this concept,
To understand this concept,
To understand this concept, imagine a multistory hotel.
imagine a multistory hotel.
The floors of the hotel are the imagine a multistory hotel.
The floors of the hotel are the imagine a multistory hotel.
permitted orbits--also referred imagine a multistory hotel.
permitted orbits--also referred imagine a multistory hotel.
to astenergy levels--o referred imagine a multistory hotel.
to astenergy levels--o referred imagine a multistory hotel.
because it takes a specificrred imagine a multistory hotel.
because it takes a specificrred imagine a multistory hotel.
amount of energy to get to that imagine a multistory hotel.
amount of energy to get to that imagine a multistory hotel.
level. of energy to get to that imagine a multistory hotel.
imagine a multistory hotel.
When the electron checks in, it

is assigned the first level.

This is the electron's normal--

or resting--energy level, what

scientists call the ground

state.

To move the electron between the

ground state and higher energy

levels, the atom must absorb

energy either through collisions

with other atoms, or by

absorbing the energy of a photon

of light.

An atom that has absorbed energy

in this way is said to be an

excited atom.

>> So an electron can be

transferred to a higher energy

state or a larger orbit about

its nucleus by giving it just

the right energy.

It can get that energy in
It can get that energy in
It can get that energy in various ways; for instance, a
various ways; for instance, a
various ways; for instance, a collision can get it up there,
collision can get it up there,
collision can get it up there, but another way of giving it
but another way of giving it
but another way of giving it that energy is with light--with
that energy is with light--with
that energy is with light--with a photon.
a photon.
a photon. But the photon has to have
But the photon has to have
But the photon has to have exactly the right energy.
exactly the right energy.
exactly the right energy. If it has too much, the electron
If it has too much, the electron
If it has too much, the electron will just let it pass
will just let it pass
will just let it pass right on by.
right on by.
right on by. It has to have exactly the right
It has to have exactly the right
It has to have exactly the right amount, and if it does, the
amount, and if it does, the
amount, and if it does, the electron will absorb it and will
electron will absorb it and will
electron will absorb it and will use that energy to put it up
use that energy to put it up
use that energy to put it up into a higher energy state.
into a higher energy state.
into a higher energy state. >> narrator: For instance, in a
>> narrator: For instance, in a
>> narrator: For instance, in a hydrogen atom, only a photon of
hydrogen atom, only a photon of
hydrogen atom, only a photon of exactly the right energy will
exactly the right energy will
exactly the right energy will send the electron to the second
send the electron to the second
send the electron to the second level.
level.
level. It takes a different, larger
It takes a different, larger
It takes a different, larger amount of energy to move the
amount of energy to move the
amount of energy to move the electron from the ground level
electron from the ground level
electron from the ground level to the third level and yet more
to the third level and yet more
to the third level and yet more to move it on to the fourth
to move it on to the fourth
to move it on to the fourth level and so on.
Since energy, wavelength, and
Since energy, wavelength, and
Since energy, wavelength, and color of a photon are all
color of a photon are all
color of a photon are all related, we can also say that
related, we can also say that
related, we can also say that only a photon of the correct
only a photon of the correct
only a photon of the correct wavelength will excite the
wavelength will excite the
wavelength will excite the atom, or, alternately, only a
atom, or, alternately, only a
atom, or, alternately, only a photon of the correct color will
photon of the correct color will
photon of the correct color will work.
work.
work. All these statements say the
All these statements say the
All these statements say the same thing: there are thus
same thing: there are thus
same thing: there are thus several different wavelengths,
several different wavelengths,
several different wavelengths, colors or energies of light that
colors or energies of light that
colors or energies of light that can be absorbed by the
can be absorbed by the
can be absorbed by the electron, each moving it to a
electron, each moving it to a
electron, each moving it to a different, higher level.
different, higher level.
different, higher level. >> Once the electron takes that
>> Once the electron takes that
>> Once the electron takes that energy and uses it to go up to
energy and uses it to go up to
energy and uses it to go up to the higher energy state in a
the higher energy state in a
the higher energy state in a larger orbit, it's immediately
larger orbit, it's immediately
larger orbit, it's immediately going to turn around and jump
going to turn around and jump
going to turn around and jump right back down.
right back down.
right back down. >> narrator: If the electron
>> narrator: If the electron
>> narrator: If the electron jumps directly back down to the
jumps directly back down to the
jumps directly back down to the ground state, it releases the
ground state, it releases the
ground state, it releases the excess energy as a photon of
excess energy as a photon of
excess energy as a photon of exactly the same energy it had
exactly the same energy it had
exactly the same energy it had absorbed.
absorbed.
absorbed. But like an elevator, it can
But like an elevator, it can
But like an elevator, it can stop briefly, and even linger
stop briefly, and even linger
stop briefly, and even linger a while at other floors along
a while at other floors along
a while at other floors along the way instead, emitting a
the way instead, emitting a
the way instead, emitting a less energetic photon at each
less energetic photon at each
less energetic photon at each stop.
stop.
stop. Since the energy levels of each
Since the energy levels of each
Since the energy levels of each type of atom are unique, the
type of atom are unique, the
type of atom are unique, the photons an atom emits during
photons an atom emits during
photons an atom emits during this process have unique
this process have unique
this process have unique energies or colors.
energies or colors.
energies or colors. By analyzing these colors using
By analyzing these colors using
By analyzing these colors using spectroscopy, we can distinguish
spectroscopy, we can distinguish
spectroscopy, we can distinguish what types of atoms are present.
what types of atoms are present.
what types of atoms are present. Spectroscopy can determine not
Spectroscopy can determine not
Spectroscopy can determine not only the chemical element
only the chemical element
only the chemical element emitting the light but also
emitting the light but also
emitting the light but also environmental factors such as
environmental factors such as
environmental factors such as the temperature and density of
the temperature and density of
the temperature and density of the atoms.
the atoms.
the atoms. To appreciate how astronomers do
To appreciate how astronomers do
To appreciate how astronomers do this requires an understanding
this requires an understanding
this requires an understanding of the different types of
of the different types of
of the different types of spectra astronomical objects can
spectra astronomical objects can
spectra astronomical objects can emit.
In the mid-18th century, a
In the mid-18th century, a
In the mid-18th century, a German scientist named
German scientist named
German scientist named Gustav Kirchhoff identified
Gustav Kirchhoff identified
Gustav Kirchhoff identified three different types of spectra
three different types of spectra
three different types of spectra through experiments, as he
through experiments, as he
through experiments, as he burned chemicals in his
burned chemicals in his
burned chemicals in his laboratory and observed the
laboratory and observed the
laboratory and observed the light they emitted.
light they emitted.
His classification now bears his light they emitted.
His classification now bears his light they emitted.
name assKirchhoff's laws.ars his light they emitted.
name assKirchhoff's laws.ars his light they emitted.
The three types of spectrars his light they emitted.
The three types of spectrars his light they emitted.
Kirchhoff observed are called:is light they emitted.
Kirchhoff observed are called:is light they emitted.
Kcontinuous spectra, emission:or light they emitted.
Kcontinuous spectra, emission:or light they emitted.
Kbright line spectra,eandsion:or light they emitted.
light they emitted.
labsorptioneortdark-line

spectra.

The easiest to understand is

actually Kirchhoff's second

law, the emission spectrum.
This deals with the absorption

of radiation by electrons in a

low-pressure gas which re-emits

that radiation at different

wavelengths.

An emission spectrum is observed

as bright lines in the spectrum.

These are caused by the
These are caused by the
These are caused by the electrons emitting photons at
electrons emitting photons at
electrons emitting photons at specific wavelengths as they
specific wavelengths as they
specific wavelengths as they move toward the ground state
move toward the ground state
move toward the ground state from higher energy levels.
from higher energy levels.
from higher energy levels. Our modern world is filled with
Our modern world is filled with
Our modern world is filled with examples of excited atoms whose
examples of excited atoms whose
examples of excited atoms whose photons.
photons.
photons. The best are neon signs, where
The best are neon signs, where
The best are neon signs, where electricity is passed through a
electricity is passed through a
electricity is passed through a tube of gas, exciting the atoms
tube of gas, exciting the atoms
tube of gas, exciting the atoms in the gas and providing energy
in the gas and providing energy
in the gas and providing energy to the electrons.
to the electrons.
to the electrons. The electrons of the excited
The electrons of the excited
The electrons of the excited atoms cycle back and forth
atoms cycle back and forth
atoms cycle back and forth between lower and higher energy
between lower and higher energy
between lower and higher energy levels, emitting photons at
levels, emitting photons at
levels, emitting photons at wavelengths that are specific to
wavelengths that are specific to
wavelengths that are specific to the type of gas inside the tube.
the type of gas inside the tube.
the type of gas inside the tube. The different gases in each tube
The different gases in each tube
The different gases in each tube emit photons at unique
emit photons at unique
emit photons at unique wavelengths, giving each a
wavelengths, giving each a
wavelengths, giving each a specific color, and, viewed
specific color, and, viewed
specific color, and, viewed through a prism, a specific
through a prism, a specific
through a prism, a specific spectrum.
spectrum.
spectrum. This is the signature of the
This is the signature of the
This is the signature of the element.
element.
element. Emission spectra are the
Emission spectra are the
Emission spectra are the fingerprints of the chemical
fingerprints of the chemical
fingerprints of the chemical elements, each with a unique
elements, each with a unique
elements, each with a unique emission spectrum.
emission spectrum.
emission spectrum. Since emission lines reveal the
Since emission lines reveal the
Since emission lines reveal the chemical composition of a gas
chemical composition of a gas
chemical composition of a gas through their unique signature,
through their unique signature,
through their unique signature, astronomers take the known
astronomers take the known
astronomers take the known emission spectra seen in the
emission spectra seen in the
emission spectra seen in the laboratory and compare them to
laboratory and compare them to
laboratory and compare them to the ones they observe
the ones they observe
the ones they observe astronomically to determine the
astronomically to determine the
astronomically to determine the composition of the source.