Download Activity 1 - Galaxies

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Activity 1 - Galaxies
1. Take a round balloon and draw on it six small galaxies, each about 5mm
across. Make your galaxies roughly evenly spaced around the balloon.
2. Choose any one of the galaxies, and mark it ‘Milky Way’ so that you
remember which it is.
3. Label the nearest galaxies around it A, B and C, and make a note of the
distances from this galaxy to its nearest neighbours.
Galaxy
Distance to the Milky
Way (before expansion)
/cm
Distance to the Milky
Way (after expansion)
/cm
Distance moved
/cm
A
B
C
4. The balloon represents space itself.
Blow up the balloon to represent the expansion of space.
5. Again check the distances from the Milky Way to its nearest neighbours.
6. Answer the following questions (in complete sentences):
a) Sketch the balloon with its galaxies before and after you blew it up.
b) If people living somewhere in the Milky Way observe the motions of their
neighbour galaxies, what will they notice? Why might they think their own
galaxy is the centre of the universe?
c) Would people in a different galaxy observe the same overall effect, or
something different?
d) As time goes by, the real universe behaves rather like this balloon. What do
you think our astronomers must have observed about the motion of our
neighbouring galaxies?
Activity 2 - Light
When space itself expands, any light waves travelling across it become
stretched.
1. Take a balloon, and use a pen to draw a wave along it.
2. Blow up the balloon to represent the expansion of space. Observe what
happens to the wave.
3. Answer the following questions (in complete sentences):
a) Sketch the balloon before and after.
b) How did the wavelength change when you blew up the balloon?
c) This effect is called ‘redshift’, because it shifts the light from objects
towards the red end of the spectrum. Explain why.
Red Shift and the Doppler Effect
The Doppler Effect is the observed change in wavelength of a wave due to the
motion of the source relative to the observer.
When the object is moving:
The waves in front of the
object get ‘squashed together’
so the wavelength decreases.
The waves behind the object
get ‘stretched out’ so the
wavelength increases.
This is how the waves from the object would be observed:
With sound this means that when a source is moving towards you, a higher pitch
sound will be heard because the wavelength is shortened and when a source is
moving away from you, a lower pitch sound will be heard because the wavelength
is longer. You can hear this effect in the DOPPLER BALL DEMONSTRATION.
With light we call this effect red shift and we can observe redshift by
looking at the spectrum of light given off by astronomical objects.
Red Shift
Violet
Sun’s
spectrum
Another
star’s
spectrum
Shifted towards the red
end
Red
The spectrum from stars for example
will have dark line appearing in them.
These dark lines indicate what
elements the star is composed of e.g.
Hydrogen. So, since the Sun is so close
to use we can consider it to be
stationary. So we can compare the dark
lines from other objects to the sun’s
spectrum. If these dark lines are more
towards the red end of the spectrum,
then we say that the light has been red
shifted and the object is moving away
from us. If the line is towards the
violet end then we say the light has
been blue shifted and the object is
moving towards us.
In astronomy the Doppler Effect is used to measure the motion of the galaxies.
The faster a galaxy moves the greater the red shift will be.
Everywhere we look galaxies are red shifted!
This was discovered by a good looking, pipe smoking American Astronomer
called Edwin Hubble in 1929 (pictured right).
This tells us that nearly all other galaxies are moving …………… from us!
Hubble also noticed that the further away the galaxy, the greater its red shift and therefore the
……………. it is moving
In fact the speed a galaxy is moving is directly proportional to its distance from us
Speed of
Galaxy
(m/s)
We call the constant that relates the
distance to the speed of a Galaxy
Hubble's constant!
Velocity = Hubble's Constant x Distance
Distance from us, (m)
Extra Info: Just for your enjoyment!
The Big Bang Theory
To explain Hubble’s extraordinary discoveries about our expanding universe,
astronomers came up with the Big Bang Theory. The Big Bang theory states that
the whole universe started from a single tiny point that expanded rapidly in an
explosion about 13 Billion years ago and is still expanding today (like the surface
of a balloon, all galaxies are moving apart from each other, there is no centre!).
Matter was thrown out in all directions forming stars and galaxies. Both Space
and time were created in the Big Bang.
However the Big Bang theory had some competition…
There are 2 main theories about the Universe.
The Big Bang Theory - All matter and energy in the entire universe and the
four dimensions of time and space, were created in an explosion from a single
tiny point about 14 billion years ago.
The Steady State Theory - The universe on a large scale does not change with
time (evolve). It has always existed and will always continue to exist looking
much as it does now. The density of the universe remains the same because as
the universe expands matter is continuously being created to fill the gap.
Questions
1. What is the main difference between the Big Bang Theory and the Steady
State Theory?
Complete the table on the following page
2. Which theory are Scientists more likely to believe?
3. Why?
Evidence for the Big Bang
Evidence
How does this support the
Big Bang Theory?
How does this support
Steady State theory?
Red Shift
Cosmic Microwave
Background Radiation
Some challenging extension ideas…
Olbers
Paradox
The Hubble
Deep Field
Abundance of Elements
The End of the Universe?
So we now think it all started with a big bang! But how will it all end? There are 2 different ideas and which one
will happen depends on how dense the Universe is. If there is there is over a certain amount of mass per bit of
space then gravity will slow the expansion and slowly drag everything back together into a “Big Crunch”. If there
is not enough mass then the Universe will continue to expand forever, everything will slowly get spread out and
the Universe will die in a “Big Yawn”!
Astronomers are trying to solve how much mass is in the Universe as we speak!
Telescopes compared
Type of radiation
Radio telescopes
Microwave telescopes
Infra red telescopes
Reflecting telescopes &
Refracting telescopes using
visible light
Ultraviolet telescopes
X-ray and Gamma ray
telescopes
What it can see
Other information
_________ Shift
Wavelength: __________________
Frequency: __________________
Pitch:
__________________
Far away galaxy
Doppler Effect
Motion
_________ Shift
Wavelength: __________________
Frequency: __________________
Pitch:
__________________
Nearby galaxy
Questions: Some of Anthony’s friends pass him in a car as he walks along the pavement. As a friendly gesture they
continuously beep their horn as they pass him. The frequency of the horn is 80Hz.
a. How does the pitch of the horn sound as the car travels towards him?
b. How does the pitch of the horn sound as the car travels away from him?
c. What is this effect called?
d. Calculate the wavelength of the sound wave produced by the horn (the speed of sound in air is 330m/s).
e. Would you expect the value of the wavelength to be less than or greater than this as the car is travelling
towards him?
f. Sketch a graph of frequency against time to show how the frequency of the horn changes as the car passes
Anthony.
g. Sketch on the same set of axes a second line to show how the frequency would change if the car were travelling
faster.
2. Samuel makes ambulance sirens for a living and is therefore very familiar with the pitch the sirens make. One day,
Tasks
Completing the first box
 Using your knowledge of the electromagnetic spectrum fill in the little boxes with the names of the
electromagnetic spectrum. (Look carefully at the diagram to help you)
 Complete the blanks showing whether the frequency is high/low or weather the wavelength is long/short for the
EM spectrum
(Frequency shows the number of waves per second and the wavelength shows the length between each ‘crest’)
Completing the second box
 To complete this box you will need a blue and red pen
 Using the knowledge that you have obtained describe how the frequency, wavelength and pitch changes for an
object/galaxy moving towards us using a blue pen
 Using the knowledge that you have obtained describe how the frequency, wavelength and pitch changes for an
object/galaxy moving away from us using a red pen
 Using the correct coloured pen colour in each wave and say whether the diagram shows a red/blue shift
Electromagnetic Spectrum
Wavelength: __________________
Frequency: __________________
Wavelength: __________________
Frequency: __________________
1.
Scientists have a theory that the universe began with a massive explosion.
What do you think scientists would do if new evidence were found that did not support this
theory? Put a tick ( ) in the box next to your answer.
A – ignore the evidence
B – change the theory straight away
C – check the evidence to make sure it is reliable
(1)
2.
Light is given out by both the Sun and a distant galaxy.
(a)
Compared to the light from the Sun, the light from the distant galaxy has moved towards the
red end of the spectrum.
(i)
What name is given to this effect?
..........................................................................................................................
(1)
(ii)
Complete the following sentence by ticking the box that is correct.
The fact that light from a distant galaxy seems to move towards the red end of the
spectrum gives scientists evidence that:
galaxies are shrinking
galaxies are changing colour
the universe is expanding
(1)
(b)
Scientists have a theory that the universe began from a very small point and then exploded
outwards.
(i)
What name is given to this theory?
..........................................................................................................................
(1)
(ii)
Which statement gives a reason why scientists think that the universe began
with an explosion? Put a tick ( ) in the box next to your choice.
At the moment it is the best way of explaining our scientific knowledge.
It can be proved using equations.
People felt the explosion.
(1)
(Total 5 marks)
3. The diagrams show the line spectrum emitted by two galaxies. Both galaxies are moving away
from Earth.
How do you know that the galaxies are moving away from us?
a
______________________________________________________________ (1)
Which galaxy, A or B, is moving away faster?
b
Give one reason for your choice.
______________________________________________________________ (1)
What does this tell you about how far away the two galaxies are?
c
______________________________________________________________ (1)
The table below gives the velocity and distance for a number of different galaxies:
Constellation
Virgo
Distance, d
in millions of light years
Velocity, v, of a galaxy
in the constellation
in km/s
72
1 200
Perseus
400
Ursa Major
900
15 000
1200
20 000
Corona Borealis
Hydra
60 000
Hubble’s Law states that v=Hd where H is the Hubble constant.
d
Use the table to find a value for the Hubble constant, H.
(1)
e
Find the velocity of the Perseus galaxy.
(1)
f
Find the missing information for the Hydra galaxy.
(1)
4. When excited, hydrogen gas emits a spectrum of electromagnetic radiation of several different
wavelengths. When measured in a laboratory on Earth one of these wavelengths is measured as
656.3nm. A physicist observes several different galaxies through a telescope and measures the
wavelength of the same part of the spectrum. He tabulates his results in the table below.
Galaxy
Wavelength /nm
A
B
C
D
E
F
656.5
657.0
656.6
658.2
660.0
656.0
a. What region of the electromagnetic spectrum does this region of the hydrogen spectra belong to?
b. Explain which galaxy has the greatest speed (use the term red shift in your answer)?
c. Explain which galaxy is closest to the Milky Way (use the term red shift in your answer).
d. One of the results contradicts our current understanding of the universe. Which one and why?
e. What should the physicist do with this result?
(1)
(1)
(2)
(2)
(1)
5. In 1965 Arno Penzias and Robert Wilson discovered the presence of Cosmic Background Radiation
(CBR) – radiation from all directions that corresponds to a body of temperature 2.7C above absolute
zero.
a. At what time was the radiation thought to have initially been created?
b. To what region of the electromagnetic spectrum does CBR now belong?
c. To what region of the electromagnetic spectrum does CBR initially belong?
(1)
(1)
(1)
d. Why did CBR belong to a different region of the electromagnetic spectrum in the early stages of
the universe?
(2)
(Total 12 Marks)
6.
The ‘steady state’ theory was once a popular alternative to the ‘big bang’ theory.
The ‘steady state’ theory suggested that the universe, although expanding, had no origin and it has
always existed. As the universe expands, a small amount of matter is created to keep the universe
looking exactly the same all of the time.
(a)
When considering the origin of the universe, what is the difference between the ‘big bang’
theory and the ‘steady state’ theory?
............................................................................................................................. ........
.....................................................................................................................................
............................................................................................................................. ........
.....................................................................................................................................
(2)
(b)
The light from distant galaxies shows a red-shift.
(i)
What is red-shift?
...........................................................................................................................
...........................................................................................................................
(1)
(ii)
Why does red-shift provide evidence to support both the ‘big-bang’ theory and the
‘steady state’ theory?
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
(c)
The ‘steady state’ theory was important in encouraging new research into the universe.
Suggest a reason why scientists were keen to carry out new research.
............................................................................................................................. ........
.....................................................................................................................................
(1)
(d)
Scientists can answer many questions about the universe, but not the question:
‘Why was the universe created?’
Suggest a reason why scientists cannot answer this question.
.....................................................................................................................................
............................................................................................................................. ........
(1)
(Total 7 marks)
Using telescopes to look into space
When we look into the night sky, we sometimes see unexpected objects as well
as planets and stars. Such objects include:

Shooting stars which are small objects from space that burn up when
they enter the Earth’s atmosphere

Comets which are frozen rocks that orbit the Sun

Stars that explode (supernova)
We can see even more in the night sky with a telescope. Telescopes collect more light than
our eyes and can magnify the images they collect. This means they can see further into space
and get more detailed images. Telescopes can be placed either on the ground or on satellites.
The images collected by ground-based telescopes tend to be quite fuzzy because the Earth’s
atmosphere dims, scatters and distorts the light. It is however very expensive to put
telescopes on satellites in space.
Telescopes can be designed to detect any type of electromagnetic wave. This advance in
technology has allowed astronomers to generate images of objects in space from the visible
light, infra-red, radio waves, X-rays and any other electromagnetic waves they emit.
Astronomers have learnt a great deal about the Universe from these images. However, not
all electromagnetic waves can penetrate the Earth’s atmosphere. This means telescopes that
detect certain electromagnetic waves must be placed in space. Each type of telescope has
its’ own strong and weak points.
Making telescopes
It is possible to make a simple refracting telescope with two lenses as shown below:
Try it out and see what you can see…
Comparing telescopes on Earth and in space
Sort the cards into advantages and disadvantages of Earth and Space based telescopes and
write the points into the correct boxes:
Earth based
Space based
Advantages
Disadvantages
Telescope questions
1. Why can telescopes see further into space and get more detailed images of the Universe?
…………………………………………………………………………………………………………………………………………………………………………
2. Why is better to place telescopes on a satellite in space rather than placing them on the
ground?
……………………………………………………………………………………………………………………………………………………………………………
3. There are two main disadvantages of putting telescopes on satellites. One is written in the
text on the previous page, the other isn’t.
a) What is the disadvantage mentioned in the text?
………………………………………………………………………………………………………………………………………………………………
b) What do you think the other disadvantage is?
………………………………………………………………………………………………………………………………………………………………
Use the tables below to answer the remaining questions.
Telescope
Type of electromagnetic
radiation detected
Electromagnetic
radiation
Does it penetrate the Earth’s
atmosphere?
Hubble
Visible light
Gamma waves
Stopped 50km above Earth’s surface
Jodrell Bank
Radio waves
X-rays
Compton
Gamma waves
Visible light
Spitzer
Infra-red
Infra-red
Only shorter wavelengths
Chandra
X-rays
Radio waves
Yes
Stopped 200km above Earth’s
surface
Yes
4. Which two telescopes could be ground-based? Why?
……………………………………………………………………………………………………………………………………………………………………………
5. Which telescopes must be placed on a satellite? Why?
……………………………………………………………………………………………………………………………………………………………………………
………………………………..…………………..…………………………………………………………………………………………………………………….
6. The Hubble telescope is placed on a satellite in space despite the fact that visible light can
penetrate the Earth’s atmosphere. Why do you think astronomers chose to do this?
……………………………………………………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………………………………………