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Chapter 21
Stars, Galaxies and the
Universe
Many sailors and different cultures have
used the stars to guide them while
traveling.
– Slaves before the Civil War used the stars to
escape to the North.
Patterns of Stars are called
CONSTELLATIONS.
Electromagnetic Spectrum
We see visible light which is only a small
part of the electromagnetic spectrum.
Light is a form of electromagnetic
radiation, or energy that can travel through
space in waves.
The longest wavelength is the radio wave.
The wavelength of radio waves can be as the size of a
mountain.
The shortest wavelength is the gamma ray.
The wavelength of gamma waves can be the size of an
atomic nucleus.
Infrared Radiation
The Sun
–Visible Light
–Ultra-violet radiation
–Infrared radiation
–Radio emission
–X-ray radiation
Waves
What is the wavelength?
Visible light has very short wavelengths,
less than one millionth of a meter.
Some electromagnetic waves are shorter
and others can be several meters long.
ROY G. BIV
If you shine white light through a prism the
light spreads out to make a range of
different colors with different wavelengths,
called a spectrum.
The electromagnetic spectrum includes:
– Radio waves
– Visible light
– X rays
Infrared waves
Ultraviolet radiation
Gamma rays
Telescopes
Telescopes collect and focus different
types of electromagnetic radiation,
including visible light.
The 2 types of telescopes we will discuss:
– The Refracting Telescope
– The Reflecting Telescope
Refracting Telescope
This telescope uses convex lenses to look
at objects in the sky.
Convex lens is thicker in the middle than
at the edges.
The larger the objective lens the more light
the telescope can pick up making it easier
to see faint objects.
Reflecting telescope
A reflecting telescope uses a mirror instead of an
objective lens.
Like an objective lens the mirror focuses a lot of
light onto a small area.
The larger the mirror the more light the
telescope can collect.
The largest visible light telescopes are reflecting
telescopes.
Spectrographs
Most telescopes today have
spectrographs.
A spectrograph breaks the light from an
object into colors and photographs the
resulting spectrum.
It can be used to determine:
– The temperature of a star
– The composition of a star
Bright Line Spectrum
Dark Line Spectrum
Characteristics of Stars
To travel to the nearest star at the speed of light
it would take 4.2 years (Proxima Centauri).
Our sun and Proxima Centauri are only two stars
that make up our Milky Way galaxy.
Our galaxy contains hundreds of billions of stars.
There are billions of galaxies in the Universe.
"The image, called the Hubble Deep Field (HDF), was
assembled from 342 separate exposures taken with the
Wide Field and Planetary Camera 2 (WFPC2) for ten
consecutive days between December 18 and 28, 1995.
1,500 galaxies at various stages of evolution.
Most of the galaxies are so faint (nearly 30th magnitude
or about four-billion times fainter than can be seen by the
human eye) they have never before been seen by even
the largest telescopes.
Leaving the Solar System, we move further out
into the Universe and discover our greater place
in space. The 2dF (2 degree field) survey shows
the positions of over 100,000 nearby galaxies.
Our Galaxy is Huge
If you could travel at the speed of light it would
take you 25,000 years to reach the center of our
galaxy.
If you left our galaxy at the speed of light it would
take you 2 million years to reach another galaxy.
A light-year is the speed light travels in one year
which is approximately 9.5 million million
kilometers.
Galactic Collision - Interacting galaxies NGC 2207
(left) and the smaller IC 2163, 114 million light-years away
in the constellation Canis Major. Observations indicate that,
billions of years from now, IC 2163 is destined to swing
past the larger galaxy again and eventually merge into it.
Example
Dime = galaxy
Universe = 2 km
Measuring the Distance of Stars
It would seem impossible to measure
objects so far away.
However astronomers have found a way.
Astronomers often use PARALLAX to
measure the distances to nearby stars.
Everyday Parallax Example
A simpler example of parallax in the works
is what you see every day when you look
at a gauge such as the speedometer in
your car or the hands of your watch. If you
look straight over the needle, it will be
exactly aligned with the number
underneath. But if you look from the side,
you might be unsure of where the needle
is pointing.
PARALLAX
1. Hold your thumb at arms length in front of your
face
and look at it with one eye closed. Notice its placement
with respect to the background.
2. Now close that eye and open the other one, and look at
the background. Notice that your thumb seems to change
position against the background -- it appears to move
across the background.
This is because your eyes are a few centimeters apart from
each other and have a different point of view. This is what
gives you Stereo vision that lets you judge the distance of an
object. The angle the object appears to move from eye to eye
gives a measure of its distance.
Most stars are so far away that they never
appear to move when viewed from the Earth.
Astronomers use these far stars as a fixed
background.
Repeat the thumb experiment, but move if
closer to your face. Notice that the closer
your thumb is to your eyes, the farther it
appears to shift in the background. Even the
nearest stars are so far away that
astronomers can only measure a very small
shift in the closest stars.
Classifying Stars
Like the sun all stars are huge spheres of
glowing gas.
They are made of mostly hydrogen.
They make energy by nuclear fusion.
4 Types of Stars:
Red Giant, Supergiant Star, Giant Star
Main Sequence Star (Medium: Our Sun)
White Dwarf
Neutron Star
Our SUN
Types of Stars
Red Giants
White dwarfs
Our Sun
It is not the biggest or the brightest star in the
galaxy.
The reason it is so bright is because of how big
it is.
When you look at stars in the sky they all
appear to be roughly the same size.
Supergiants
Some stars are much larger than
our sun and others are the size of
Earth.
Astronomers use size along with
temperature and brightness to
classify stars.
– Very large stars are called Giant
Stars or Supergiants.
– Example: Betelgeuse
Red Giants
Betelgeuse
If this star was
our Sun it would
extend all the
way to Jupiter.
Eventually our Sun will start to run out of
hydrogen. The core is now composed mostly of
helium nuclei and electrons, and begins to
collapse, driving up the core temperature, and
increasing the rate at which the remaining
hydrogen is consumed. The outer portions of the
star expand and cool, producing the Red Giant
phase.
White Dwarfs
White dwarf stars
about the size of
Earth.
Neutron Stars
A neutron star are
only 20 kilometers
in diameter (12.4
miles),
Color
A star’s color reveals it’s temperature.
Hot objects on Earth display the same
range of colors.
Coolest Stars – about 3,200 degrees Celsius – reddish
Middle range stars – about 5,500 degrees Celsius – white
Hottest Stars – over 10,000 degrees Celsius – slightly bluer
than the sun (IN CLASS EXAMPLE)
Brightness Of Stars
Stars differ in brightness.
The brightness of a star depends on its
size and temperature.
How bright a star is from Earth depends
on:
How bright the star actually is
How far the star is from Earth
Brightness
Brightness can be described in two
different ways:
– Apparent magnitude
– Absolute magnitude
Apparent Brightness
This is how bright a star is seen from Earth.
Absolute Brightness
The brightness of a star if it were a
standard distant away from the Earth.
Apparent Brightness
This is how bright a star is seen from Earth.
Hertzsprung-Russell Diagram
(See Overhead)
These two gentlemen made graphs to determine
if the temperature of stars and their brightness
were related.
They plotted different stars onto the graph and
noticed a pattern.
The graph they made is still used 100 years later
and is called the Hertzsprung-Russell diagram
or H-R diagram.
More than 90% of the stars are Main Sequence
stars like our sun.
Stars
Stars
Stars do not live forever.
Stars
Each star is born, goes through it’s life and
dies.
Astronomers can not watch a star for a billion
years to see all of the stages, but they look to
see the difference between stars.
A Star is Born
Stars are made of large amounts of gas in small space.
A nebula is a large amount of dust and gas over a large
area. All stars start out as nebulas.
Gravity pulls some of the gas and dust in the cloud
together.
The contracting cloud is then called a PROTOSTAR,
meaning the earliest stage of a star’s life.
A star is born when the contracting gas and dust
become so hot that nuclear fusion starts.
How long a star lives depends on how
much mass it has.
Smaller stars last longer. Think of a small
car, it has a small gas tank, but also burns
gas slowly compared to a big car.
Small mass stars use up their fuel more
slowly and live longer.
Stars less massive than our Sun can last
for up to 200 billion years.
Our medium sized star (Sun) will last
around 10 billion years.
Stars that is 15 times more massive than
the Sun may last only 10 million years.
Death of Stars
When a star begins to run out of fuel, the center
of the star shrinks and the outer part of the star
expands.
The star will become a Red Giant or a
Supergiant.
When a star runs out of fuel, it becomes a:
– Black dwarf
– Neutron star
– Black hole
The Life of a Star
White Dwarf
Small mass and medium mass stars take 10
billion years or more to use up their nuclei fuel.
Then their outer layer expand and they become
red giants.
Eventually the outer parts grow bigger and move
out into space leaving the blue hot core of the
star behind. This is called a white dwarf.
White Dwarf
About the size of Earth
Same mass as our sun, but
approximately one millionth the
volume
Very dense (one spoonful of
material from a white dwarf will
have as much mass as a large
truck.
White dwarfs do not have any fuel
left, but they glow faintly from left
over energy.
When a white dwarf stops glowing
it is dead. Then it is called a black
dwarf.
BLACK DWARF
Neutron Star
A dying giant or super giant can suddenly
explode.
Within hours, the star blazes millions of
times brighter.
This explosion is called a supernova.
Supernova
Supernova
After a supernova, some of the material from the
star expands into space.
This material may become apart of a nebula
The nebula can then contract to form a new
“recycled” star.
Astronomers think the sun began as a nebula
that contained material from a supernova
explosion.
Neutron Star
After the star explodes, some
of the material from the star is
left behind.
This material forms a Neutron
Star.
Neutron stars are even smaller
and more dense than white
dwarfs.
A neutron star may contain as
much as 3 times the mass of
the sun, but only be about 20
kilometers wide.
Black Holes
The most massive stars – those having more than 40 times the
mass of the sun- become black holes when they die.
After this kind of star supernovas more than 5 times the mass of the
sun may be left. The gravity of this mass is so strong that the gas is
pulled inward, packing the gas into a smaller and smaller space.
Eventually 5 times the mass of the sun becomes packed into a area
with a diameter of 30 kilometers.
At that point, the gravity is so strong that nothing can escape, not
even light.
The remains of the star is a black hole.
http://www.ioncmaste.ca/homepage/resour
ces/web_resources/CSA_Astro9/files/html/
module1/module1.html
Pulsars
In 1967 Jocelyn Bell detected an object in space
that gave off radio waves (Some people thought
they were messages from aliens).
Astronomers discovered that the source was a
neutron star. A small object that is left over
when a giant star explodes.
Neutron stars that pulsate radio waves are
called PULSARS.
Quasars
Quasars are very bright, but also very far away
approximately 12 billion light years.
What could be so far away yet so bright?
Astronomers believe that quasars are distant galaxies
with black holes as their centers with the black hole
having a mass that is a billion times that of the sun.
As the enormous amounts of gas revolve around such a
black hole, the gas heats up and shines brightly.
Milky Way Galaxy
Star Systems and Galaxies
More than half of all stars are members of
groups of 2 or more stars called star
systems.
Stars with two stars are called double
stars or binary stars.
Those with three stars are called triple
stars.
Eclipsing binary is where one star blocks out the
light from another.
Astronomers are have found other stars with
planets around them. They are able to tell that
these stars have planets because of how the
planet effects the star.
Only large planets have been detected so far
(half the mass of Jupiter). A small planet would
be difficult to detect because it would have little
gravitational effect on the star it revolved around.
3 types of Galaxies
Spiral Galaxies: Has the shape of twin
spirals.
Elliptical Galaxies: Look like flattened
balls. These galaxies have billions of
stars, but little gas and dust. Because of
the little gas and dust new stars cannot
form, so most elliptical galaxies contain old
stars.
Irregular Galaxies: Do not have regular
shapes.
Spiral Galaxy
Elliptical Galaxy
Irregular Galaxy
Discovered by E.E. Barnard in 1884, NGC 6822 is also known as Barnard's
Galaxy. It is located 1.6 million light-years away in the constellation Sagittarius.
In this image, taken by the 4-meter Blanco Telescope in Chile, the galaxy glows
blue with the light of countless massive, hot stars. Pinkish bubble nebulae
hang along the galaxy's fringes.
Big Bang
10 to 15 billion years ago the universe was
a single point that was hot and dense.
A enormous explosion formed the universe
about 10 to 15 billion years ago.
The universe is continuously expanding
and getting larger.
Formation of Our Solar System
As the universe grew, gas and dust spread out in
our galaxy.
About 5 billion years ago, a giant cloud of gas
and dust, or nebula, collapsed to form the solar
system.
– Slowly the nebula shrank to form a spinning disk. As
gravity pulled some of the gas into the center of the
disk, the gas became hot and dense enough for
nuclear fusion to begin and the sun was born.
– Elsewhere in the disk the gas and dust formed the
planets.
Future of the Universe
One Theory: It will continue to expand
and all of the stars will run out of fuel and
burn out and the Universe will be cold and
dark.
Second Theory: It will begin to come back
together and be called the “big crunch.”
All the matter of the universe will be
crushed into an enormous black hole.
Future of the Universe
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