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Earth Science 11: The Universe
Text: Chapter 16 *This is required reading!
Part A: What is the Universe?
At a basic level, it is the collection of dust clouds (nebula), stars, stellar
remnants and galaxies.
Cosmology is the study of the universe and it goes beyond this. It
investigates the universe’s properties, structure and evolution.
What are some questions about the universe that we want answers to?
-Age, evolution, will it end?, etc…
-Much of the answers to these questions will come from observations of stars and galaxies!
Let’s have a quick look at the creation of the universe before we investigate its components in more
depth...
Big Bang Theory
-The Big Bang Theory is the model that most accurately described the creation and current state of the
universe.
-The Universe existed in a hot, dense state and around 13.7 bya (billion years ago) began to expand, cool
and evolve into its current state.
*Read Chapter 1 of A Short History of Nearly Everything by Bill Bryson for a vivid description of what
the Big Bang was like.
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Part B: Light and Electromagnetic Spectrum
-The light produced by stars reveals a vast amount of information about them and their place in the
universe.
1. What is Light?
-Light is a form of electromagnetic
radiation. This means that it:
a) Travels in waves (at the speed of light:
300,000 km/s)
b) Does not need a medium for travel = can
move through space.
-Electromagnetic waves emitted by an
object tell us about the elements present in
the object and the object’s motion.
2. Spectroscope and Types of Visible
Spectra
-A spectroscope is an instrument used by
astronomers to learn about the composition and motion of stars.
-A spectroscope contains a diffraction grating that separates visible light into a spectrum of colours (each
colour represents a different wavelength in the electromagnetic spectrum).
-There are three types of spectrums that can be produced through this process:
a) Continuous Spectrum
-Glowing solids, glowing liquids and the hot/compressed gasses inside of stars.
-Examine the classroom lights using the spectroscope.
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b) Emission Spectrum
-Only specific wavelengths of light are emitted by hot gas.
-Each element has its own unique emission spectra = they can be identified by light!
c) Absorption Spectrum
-Is a combination of the Continuous and Emission spectra, with the cold gases in the outer-atmosphere of
a star absorbing the same wavelengths it would emit when heated.
-Dark spectral lines can reveal the composition of the star’s outer-atmosphere.
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-Absorption spectra can also be useful
in determining the chemical
composition of gas clouds and
planets’ atmospheres.
3. Stellar Distances
-There are two ways that astronomers
determine the distance of stars from
an observer:
a) Doppler Effect
-The Absorption Spectrum produced
by a star or planet changes depending
on whether the star is moving towards
or away from the observer.
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-On the continuous spectrum below, draw the absorption spectrum for a star. Next, indicate what
direction the spectral lines would move if the star was moving towards Earth. *Slinky Demo!
-If you understand this video (The Big Bang Theory – The Doppler Effect), then you’ve got the concept!
b) Stellar Parallax:
-Parallax is the apparent movement of an object due to the movement of the observer.
-Try it: Close one eye and align your index figure with an object in the distance. Without moving your
finger, view the object with the other eye and notice that its position appears to have changed.
-Astronomers use this principle to determine the distance of stars from Earth, with the closest stars having
larger parallax angles.
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4. Star Brightness
-Stars are categorized by their brightness in
two ways:
a) Apparent Magnitude
-How bright stars appear from Earth.
-Stars are organized into magnitudes, with a
difference of 2.5x brightness between
magnitudes.
-The more negative the apparent magnitude
of a star, the brighter it is.
b) Absolute Magnitude
-As telescopes improved scientists realized
that many more stars exist in the Universe
than those close to Earth. This means that
distance now needed to be factored into
stellar magnitudes.
-Absolute magnitude is the brightness stars would have if they were all 32.6 light-years from Earth.
-Explain how and why the brightness of Earth’s Sun changes under these different systems.
-Apparent Magnitude: Very bright as is so close to Earth. (Size, temp, distance)
-Absolute Magnitude: Less bright than originally ranked because of its proximity to Earth. (Size, Temp)
5. Star Colour and Temperature
-Stellar temperature can be determined
by the colour of the light emitted.
-Hot stars with a surface temperature
above 30,000 K emit short wavelength
light and appear blue.
-Stars with a surface temperature
between 5,000 and 6,000 K appear
yellow.
-Stars with a surface temperature less
than 3,000 K emit long wavelength light
and appear red.
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Part C: Star Categorization
-The first stars formed 400 mya, but
before we look into this process we need
to first learn how stars are categorized.
-Star’s live for billions of years and can
be categorized into one of several
different stages depending on the
characteristics they have.
-The Hertzsprung-Russel Diagram
depicts the stages of stellar evolution
using luminosity (energy emitted per
unit time) and temperature.
*Important: Luminosity is a product of
temperature and mass!
*Watch the H-R Diagram Smartfigure.
Main Sequence Stars: 90% of all stars; Fuse hydrogen into helium. Vary in temp, size, luminosity, etc.
Blue/Red Giants: 10 to 100 x the sun’s diameter; Size lets them be very luminous despite temperatures.
Blue/Red Supergiants: 100x the sun’s diameter; Luminous regardless of temp due to size.
White Dwarfs: Stars at the end of their lives; Outer atmosphere is lost and only glowing core remains.
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Part D: Star Evolution
*Important: A star’s life is ruled by
gravity!
1. Stellar Nebulae
-Eventually, the Universe cooled enough
for gravity to be able to pull gas (H and
He) and dust (heavier elements) together
into massive clouds called nebulae. The
star producing Eagle Nebula is pictured
right.
-Gravity causes nebula to contract and
this causes an increase in the gases’
temperature (gravitational energy is converted into
thermal energy).
2. Protostar Stage
-Protostars are created when gas is heated to a high
enough temperature to radiate long-wavelength red
light.
-Why are protostars not considered “real” stars?
-Do not undergo nuclear fusion of four hydrogen into
one helium.
3. Main-Sequence Stage (Hydrogen fusion)
Nuclear fusion releases an immense amount of
heat:
a) What effect would this have on the gas inside
of the star?
-Volume would increase.
b) Is this effect a good, bad or neutral?
-Good, as the outward pressure exactly balances the inward pull of gravity. As long as this balance in
maintained, the star is stable.
-Stars remain in the main-sequence for 90% of their life and rapidly evolve/die when they run out of
hydrogen to fuse.
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4. Red Giant Stage
-Without any hydrogen to fuse, what would
happen to the volume of a star’s core?
-Decrease as gravity is no longer balanced by
outward pressure of H fusion.
-What effect would this have on the temperature
of the star’s core?
-Increase as gravitational energy is converted
into thermal energy. (Increased molecule
collision in a smaller volume).
-Some of the additional energy is directed
outwards and causes an increase in the hydrogen
fusion rate outside of the core. This, in turn,
generates more heat and causes the gaseous
outer shell to expand and cool.
-The balance between gravity and gas pressure is eventually reformed and the increase in temperature in
the star’s core allows it to fuse He into C (massive stars will eventually fuse all elements up to iron on the
periodic table).
5. Burnout and Death
-Stars eventually run out of nuclear fuel and eventually
collapse due to the force of gravity. However, stars have
different deaths depending on their mass.
*Watch the Star Death Smartfigure.
6. Stellar Remnants
*Take your own notes from text 16.5 on stellar remnants.
a) White Dwarfs:
-Low to Medium mass stars use their fuel and are collapsed
by gravity. Eventually held stable by electron degeneracy
pressure (electrons are pushed together, but negative charges repel each other).
b) Neutron Stars:
-Produced by supernova events as a star’s core collapses inwards. Electrons are forced even closer
together and combine with protons in the nucleus to produce neutrons.
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-High surface temperatures, but not very large = low luminosity.
-Pulsars: Neutron stars spin faster as their size decreases. Radio waves generated by rotating magnetic
field are concentrated into narrow zones that align with the star’s magnetic poles.
c) Black Holes:
-Stars larger than 3x the sun have such a large gravitational pull that neutrons can’t exert enough pressure
against it. Star collapses into a black hole.
-Very hot, but so dense (such high gravity) that light can’t escape.
-Matter pulled in releases x-rays as it becomes heated.
*Video: Life and Death of Stars. Complete the note sheet provided.
Part E: Stellar Investigations
-Stars are one of the most obvious
components of the Universe and through
studies of their characteristics have
revealed a great deal about it.
Constellations
-Constellations are human’s way of
making sense of the stars that fill our sky
and their movements.
-What are some of the important purposes
constellations have had for humanity?
-Navigation, Seasonal patterns (Agriculture,
migration), cultural myths.
-Earth’s motions cause the apparent motion of the
constellations:
a) Earth rotation is from west to east. This
causes the stars to “move” from east to west.
b) Earth’s revolution causes the seasonal
movement of the stars.
-Why do some stars, like Polaris (North Star), never
seem to change their position in the sky?
-Directly above Earth’s axis (poles) and as such in the centre of Earth’s rotation.
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Part F: Galaxies
-Galaxies are collections of dust and gas clouds, stars, stellar remnants and planets held together by
gravity.
-There are three basic types of galaxies:
Galaxy Type
Spiral
Elliptical
Shape
Characteristics
-Flat, disc-shaped with arms extending from
nucleus.
-Older stars (yellow colour) are found in the
centre and younger ones (blue colour) in the
arms.
-Elliptical shape, lack arms.
-Include the largest and smallest galaxies.
-Large elliptical galaxies contain older, lowmass stars and little dust and gas clouds = low
star formation rates. This makes them look
yellow to red in colour.
-Product of spiral and elliptical galaxies being
distorted by a larger neighbour to create a
galaxy with no symmetry.
-Stars are smaller, fainter and irregularly
placed.
Irregular
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Part G: Big Bang
Theory
-The Big Bang Theory
states that all matter
existed in a hot, dense
state and expanded
outwards around 13.7
billion years ago.
-Where did elements
heavier than H and He
come from to form our
planets?
-Death of stars; Matter
fused into heavier states
by nuclear fusion and
expelled into space by
supernovae explosions.
-What evidence do we
have to support the Big
Bang Theory? Use your
text and
http://www.bbc.co.uk/science/0/20932483 as resources.
1. Doppler Effect
*View the Doppler Effect Smartfigure and take your own notes below.
-All galaxies are red-shifting away from Earth, with those farthest away red-shifting at a
faster rate. This is best
explained by the idea of an expanding
universe.
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2. Cosmic Background Radiation
-Universe was extremely hot when created and
this produced electromagnetic radiation (light) that
was high energy and short wavelengths. Waves
stretched by expansion of universe to that now
long-wavelength radio waves (microwave
radiation). This has been detected and found to
fill the entire universe.
*Read pages 16-19 of A Short History of Nearly
Everything to learn how CBR was discovered.
3. Telescopes
-Looking out into space is like looking back in time as it takes millions to billions of years for the light
from objects far away from Earth to reach us. As such, when the light does reach us we are seeing the
object as it looked in the past.
-Modern telescopes are powerful enough to see objects many billions of light years away, close to the
time of the Big Bang. Recently discovered gas clouds of this age are primarily made of H and He, which
is consistent with the Big Bang Theory.
*For more information on this type of evidence, read the article
http://www.sciencedaily.com/releases/2012/09/120919135419.htm
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-The earliest observations of the stars were to group them into recognizable patterns
are the most obvious component of our universe and through analysis have revealed a lot about the nature
of the universe, etc.
Constellations for direction, etc.
Then more scientific things, in order to discovery.
Part C: Stars
-Classification
-Evolution
-Remnants
-What they tell us about the universe
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look at a few basic ideas before we investigate the Universe in more depth:
Size
Contents
What is the Universe?
-Many galaxies containing stars, planets, nebula, etc.
What are some things that we want to know about it?
-Age of Universe (Big Bang Theory says that si 13byold,l however big, etc).
-Some of the answers to these questions have been discovered by examining stars.
Life and Death of Stars
Characteristics of stars that tell us about the universe
Stars
-Where they come from
-Classification
-Stellar Evolution
-Stellar Remnants
-Galaxies
-Big Bang Theory
Star Characteristics and what they mean:
Distance:
-Estimated by Doppler Effect, Triangulation, Parallax
-Also need to know about AU, Light year
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-Doppler Effect: Distance of stars from the observer
-
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