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OCR 21st Century Science
Unit P1a Revision
The earth in the universe
The eight planets of our Solar System
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Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
As well as the eight planets, the solar system is also made
up of asteroids, dwarf planets, comets and moons
Different Orbits
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Mercury = 88 days
Mercury
Venus
Earth
Mars
Mars = 687 days
Pluto =
Jupiter
90,500 days
Saturn
Uranus
Neptune
Pluto
Asteroids
An “asteroid belt” lies between Mars and
Jupiter. But what is an asteroid?
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Comets
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Comets are balls of dust and frozen
gas. They have very elliptical orbits:
Notice how the tail always points away from the sun!
The Solar System summarised
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What makes up our solar system? Complete the following mind
map with what you now about each object:
The solar system
Solar systems, galaxies and the Universe
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Our planet (around 13,000km diameter and 4500 million
years old) is pretty small compared to...
OUR SUN (100 times wider
and 4.6 billion years old),
which is small compared to…
THE UNIVERSE, which
contains billions of galaxies and
is 14,000 million years old.
THE MILKY WAY, which
contains at least 200 billion
stars and is 100,000 light
years across, which is small
compared to…
How to make a solar system
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Stage 1: Nebulae
A nebulae is a collection of dust, gas and rock.
Some examples of nebulae…
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Stage 2: Throw the nebula together
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Gravity will slowly pull these
particles together…
As they move inwards their
gravitational potential energy
is converted into heat and a
big object (PROTOSTAR) or
smaller objects (planets,
asteroids etc) are formed
Stage 3: Make a star
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In a star the forces of
gravitational attraction
pulling the particles inwards
are _________ by forces
acting outwards due to the
huge __________ inside the
star.
Stars are basically ________ reactors that use _______
as a fuel. During its main sequence a star will release
energy by combining hydrogen and helium nuclei (light
elements) into _________ elements.
Any element in space that is heavier than helium is
thought to have been made in a star.
Words – heavier, balanced, hydrogen, nuclear, temperatures
Observing the Universe
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All of these methods rely on detecting radiation from stars.
The Light Year
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Distances in space are so big that they are measured in units
called “light years”:
1 light year = the distance
travelled by light in one yar
Q. If light travels through space (i.e. A vacuum) at 300,000
km/s how far is one light year?
Because of this, when we see stars in the night sky we are
actually seeing them as they were in the past.
Distances in space
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The Sun, our closest star, is 1.6x10-5 light years
away from us.
The next closest star, Proxima
Centauri (4.2 light years away)
The centre of our galaxy, the Milky Way, is
around 26,000 light years away.
The Andromeda Galaxy (our closest galaxy)
– approximately 2.5 million light years away
Measuring distance using brightness
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When I look at these stars some appear brighter than
others. This because they are either brighter stars or
closer to me.
For example, the star Antares is 10,000 times brighter
than the sun but it is 500 light years away from me, so it
is only the 15th brightest star in the night sky.
Measuring distances to stars
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1) Relative Brightness
The further away a
star is the dimmer it
is. Simple.
2) Parallax
Parallax is the
apparent change in
position of closer
stars due to the
Earth moving around
the sun.
Distant
stars
Nearby star
Problems in Measuring Distances
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1) Light pollution and other
atmospheric conditions can
interfere with observing stars:
2) Stars are simply very far away so the
angles involved in using techniques like
parallax are very small:
How our Earth and the Sun
compare to others…
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How did the universe begin?
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Scientists believe that the universe began by a “big bang”
around 14 billion years ago:
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Evidence about the origins of
the universe…
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Source of
light
“Spectra”
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If you pass the light through a gas something
different is seen…
helium
Some wavelengths of light
are absorbed by the gas –
an “absorption spectrum”.
If the light source is moving away the absorption
spectra look a little different…
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Before
helium
helium
After
The absorption lines have all been “shifted”
towards the longer wavelength end (red end)…
This is called red
shift. The faster
the light source
moves the further
its light will be
“shifted”
Before
After
A similar effect happens with sound –
this is called “The Doppler Effect”
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Red Shift simplified
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Basically, if I walk towards you I’ll look
slightly more blue. Then, if I walk away
from you, I’ll look slightly more red!!
Let’s try it…
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Light from different stars and from the edge
of the universe also shows this “red-shift”.
This suggests that everything in the universe
is moving away from a single point.
This is the BIG
BANG theory
Red shift summary
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Light from other galaxies has a longer _________ than
expected. This shows that these galaxies are moving ____
from us very quickly. This effect is seen to a greater
extent in galaxies that are _______ away from us. This
indicates that the further away the galaxy is, the ______
it is moving.
This evidence seems to suggest that everything in the
universe is moving away from a single point, and that this
process started around 15 _____ years ago. This is the
____ ________ Theory.
Words to use – faster, away, big bang,
billion, wavelength, further
Hubble’s Law
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The speed at which galaxies are
moving away from us is proportional
to their distance from us.
In other words, the further away
they are, the faster they go.
Edwin Hubble
1889-1953
Big Bang Theory
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Some scientists have explained that red shift can actually be used to
support the Big Bang Theory – this explanation is based around the rates
of expansion and contraction of different galaxies. If our neighbouring
galaxy is expanding at a different rate to the Milky Way then it will appear
red or blue-shifted.
So Mr President, red shift
shows us that galaxies are
moving and therefore we
assume that space itself is
expanding. Elementary!
Stephen Hawking, 1942 -
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The end of the Universe
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There are some theories about how the
universe will end but its difficult to tell due
to difficulties in measuring objects that are
so far away:
“The big crunch” – if there is too much mass (i.e. too much
matter) the universe will collapse under its own gravity. It
may then do another “big bang” – this is the “oscillating
universe” theory.
“Expanding Universe” – if there isn’t enough mass in the
universe then it will just keep on expending forever.
If there is just the right mass in the universe then it will
reach a fixed size.
The End of the Universe
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Basically, how the universe will end
depends on its “energy-mass density”.
Size of universe
Stephen Hawking
Now
Open universe
Critical
density
Closed
universe
Time