Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Exoplanets: Lesson Plan
A lesson on detecting exoplanets for Key Stage 4 pupils (and high-achieving year 9 pupils).
This lesson plan has been developed by the Jodrell Bank Discovery Centre as part of the Science and
Technology Facilities Council’s (STFC) Science and Society Large Award project Big Science: Big
Telescopes.
This lesson plan is free for teachers to download and share.
This lesson is designed to excite and inspire pupils by engaging them with examples of the ‘Big
Science’ carried out with the ‘Big Telescopes’ funded by STFC.
Some of the Big Telescopes with funding from STFC include the VLT (Very Large Telescope), ALMA
(Atacama Large Millimetre/sub-millimetre Array), e-MERLIN (the UK's facility for high resolution
radio astronomy observations), E-ELT (European Extremely Large Telescope) and SKA (Square
Kilometre Array).
The Lovell telescope at Jodrell Bank, part of e-MERLIN.
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Introduction
Exoplanets are a very current and intriguing area of astronomy. An exoplanet refers to a planet
orbiting around another star in our galaxy (i.e. a star which is not the Sun). It is estimated there are
more than 200 billion stars in our Milky Way galaxy1. It is now thought that most of these stars have
planets orbiting around them2. The vast majority of these exoplanets cannot be imaged directly. This
is because planets are much smaller and dimmer than their parent stars, which completely outshine
them. In order to detect exoplanets astronomers must use indirect methods; looking for clues in the
star’s light that suggest exoplanets may be present. As of August 2013, scientists have detected 929
exoplanets3.
In this lesson your pupils will be introduced to the use of telescopes to do astronomy across the
whole electromagnetic spectrum and the advantages of big telescopes. They will then explore the
transit method of detecting exoplanets (either practically, or using real astronomical data) and use
mathematics to calculate some of the properties of their exoplanet. The lesson concludes by
considering the big question: are we alone in the universe?
Artist’s impression of an exoplanet
1
http://www.space.com/19915-milky-way-galaxy.html
http://www.bbc.co.uk/news/science-environment-16515944
3
You can find out the most up-to-date number at http://exoplanet.eu/catalog/
2
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Learning Objectives





All
Most
Some
Translate advantages of big telescopes to the human eye.
Comprehend that visible light and radio waves show different phenomena.
Interpreting data [either from practical activity, or provided information] to collect meaningful results.
Mathematically analysing results to conclude properties of an exoplanet.
Evaluating analysis method to identify underlying assumptions and their potential impacts on the conclusions [extension activity].
Suggested timeline of activities (times dependent on group)
Time &
Activity
Slide
0-3 mins
1
Starter
3-5 mins
Lesson
intro
2
Activity details
Teaching notes
Ask pupils to guess
how many planets
there are in our
Milky Way galaxy.
Pupils could record their guesses in a number of ways, e.g. post-it notes,
mini-whiteboards. They could discuss in groups or answer individually.
Define term
‘exoplanet’ as a
planet that orbits
another star in our
galaxy.
Introduce contents
of lesson (and
objectives if
required).
It is currently not known how many planets there are in the Milky Way,
but it is estimated to be upwards of 50 billion. As of August 2013,
astronomers have detected 929.
Differentiation
Some pupils may be unfamiliar
with the term ‘galaxy’.
A galaxy is a collection of many
stars, bound by gravity. Our
galaxy is the Milky Way and it
contains around 200 billion stars.
In Part 1 pupils will learn about the use of telescopes in astronomy
generally and why big telescopes are advantageous.
In Part 2 pupils will focus on one particular area of current astronomy
research; exoplanets. They will collect (or be given) data and analyse it
mathematically to calculate some properties of an exoplanet.
N/A
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
3
Light travels through space as an electromagnetic wave, but there are
other EM waves travelling through space.
4
Objects can emit any EM waves, such as radio waves, microwaves,
infrared waves, etc… These other EM waves are identical to light, except
they are a different size. A slinky could be used at this point to
demonstrate waves with different wavelengths4. [This links to GCSE
physics specifications]
5-8 mins
Teacher-led
definition of some of
the concepts used in
the lesson.
Why do
we need
so many
telescope
s?
5
4
This is Centaurus A; a galaxy around 13 million light years from Earth.
When we look at it with visible light, we see an ordinary galaxy, but when
we look with radio waves we see great blasts of material being thrown
out the top and bottom of the galaxy.
N/A
This suggests there is an active supermassive black hole at the centre of
Centaurus A5, which we wouldn’t know if we only looked in visible light.
It’s only by looking at all the waves that we get the full picture about
what is going on, so we need lots of different types of telescopes to look
at the different waves.
Animation of this demonstration: https://www.youtube.com/watch?v=3BN5-JSsu_4
An active black hole means the black hole is currently swallowing matter. Some material around the black hole gets accelerated by the huge gravitational field and blasted
out as huge jets travelling at nearly the speed of light. More details on black holes at http://curious.astro.cornell.edu/blackholes.php
5
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
8-10 mins
6
The Lovell telescope at Jodrell Bank (in Cheshire, UK) is a radio telescope,
built 1952 - 1957. It is still used today and at 76m in diameter, it is the
third largest steerable telescope in the world, but why does it need to be
so big?
7
Larger telescopes can collect more light and therefore see dimmer
objects (that is, objects that are further away), but they also create
sharper images6.
Why
build big
telescope
s?
Teacher-led
examples of how this
data is collected in
real life.
8
This mini plenary assesses the first two learning objectives: Translate
advantages of big telescopes to the human eye. Comprehend that visible
light and radio waves show different phenomena.
10-13
mins
9-10
Mini
Plenary
6
7
With modern technology (supercomputers and fibre-optic data
networks) it is preferable to make many linked smaller telescopes, rather
than single large ones. The Square Kilometre Array (SKA) will be the
largest radio telescope in the world, built of over 3000 smaller dishes,
spread across the deserts of Australia and South Africa7. It will act like
one giant telescope thousands of kilometres wide! A telescope that size
would be impossible to build as one giant dish! The SKA will be so
powerful, it will be able to detect organic molecules in space.
Two short questions
which test pupils’
understanding of
science concepts.
Pupils could discuss answers in groups, before providing verbal feedback,
or could ‘think-pair-share’. Pupils could answer individually on
whiteboards, or post-it notes.
If pupils have not achieved the objectives, peer help could be used, or
some other consolidation activity could be used (see ‘Additional
resources’).
N/A
Lower: May find it easier to draw
their answers. Or, teachers could
provide multiple choice options
that pupils vote on.
Higher: Pupils could use this
activity as written exam practice;
peer assessment could be used to
give feedback on their answers.
The explanation for this is A-level physics, so it is not addressed here, but it can be found at http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/cirapp.html
More information on SKA can be found at http://www.skatelescope.org/
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
11
13-15
mins
Set practical activity
in context, then
provide instructions
for a successful
practical.
Practical
intro
12
What do we need big telescopes for? One of the things astronomers are
currently using them for is hunting for exoplanets. An exoplanet is a
planet orbiting around another star in space. We can’t see these directly,
because they are so small compared to their star, which emits a massive
amount of light. Astronomers need to look for changes in the star’s light
to show a planet is there. These changes are tiny, so very sensitive, big
telescopes are required to detect them.
One method to detect exoplanet is the transit method. This is what the
practical activity will represent. This involves looking for a tiny, regular
‘dip’ in a star’s light as a planet passes in front of it.
See ‘Practical instructions’ for how to set up and run the practical activity.
If not completing the practical activity, see ‘Using supplied results’.
Higher: May be able to collect
results from open questions such
as, “how can the equipment on
the table be used to simulate an
exoplanet orbiting a star?” They
perhaps could also construct their
own results table, rather than
using the supplied worksheet.
Pupils can record their results using the supplied pupil worksheet. See
‘Reading the data’ for information on how pupils should read off their
results from the data they collected.
15-30
mins
N/A
Practical
activity
Lower: May require a step-bystep set of instructions on how to
complete the practical activity,
which they can refer to during the
practical.
Pupils to complete
practical activity.
In the practical activity, pupils should complete questions 1-5 of their
worksheet.
This assess the third learning objective: Interpreting data [either from
practical activity, or provided information] to collect meaningful results.
Pupils could be placed in mixed
ability groups, for peer support.
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Firstly, to make their results more realistic, pupils should multiply their
measured orbital period (in seconds) by 100 days (e.g. 2 seconds becomes
200 days). Then, by dividing by 365.25, they have the fraction of an Earth
year their planet takes to complete one orbit of its star.
13
30-38
mins
14
Analysing
results 1
15
8
9
Pupils use a
mathematical
equation to analyse
their results and
determine how far
away from its star
their exoplanet
would be.
Pupils now use a simplified version of Kepler’s third law8 to calculate how
far away from its star their exoplanet is. Please note this relationship only
works if the orbital period is measured in Earth years and the distance is
measured in AU (‘Astronomical Units’: 1 AU is the distance between the
Sun and the Earth9). Also, this simplified version of Kepler’s third law only
works for planets orbiting the Sun. Pupils should assume that their star is
identical to the Sun.
This activity assesses the fourth learning objective: Mathematically
analysing results to conclude properties of an exoplanet.
This activity requires pupils to
rearrange an algebraic equation.
Some pupils may require support
with this.
Pupils could arrange themselves
by self assessment into a
confident and un-confident
group; so that extra support can
be given to those who require it.
Once they have estimated a value for the distance, pupils can compare
their exoplanet with our Solar System, to get an idea of where their
exoplanet would lay.
Also called the law of periods: http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c6; More about Kepler at http://en.wikipedia.org/wiki/Johannes_Kepler
Definition of the AU http://neo.jpl.nasa.gov/glossary/au.html
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Pupils have already calculated B, the fraction of starlight blocked by their
exoplanet when it passes in front of their star.
38-46
mins
16
Analysing
results 2
Pupils use a
mathematical
equation to analyse
their results and
determine the
diameter of their
exoplanet.
This fraction will be equal to the ratio of the area of the star’s surface
blocked by the exoplanet (or simply, the area of the exoplanet) to the
area of the star.
This activity also requires pupils to
rearrange an algebraic equation,
more difficult than the last.
By using this ratio and substituting in the equation for the area of a circle,
pupils can now calculate r, the radius of their exoplanet.
Before attempting this activity,
pupils could reassess their
confidence at rearranging
algebraic equations. Some may
wish to switch groups, depending
on how difficult or easy they
found the previous activity.
Pupils should once again assume their star is identical to the Sun, by using
the radius of the Sun as R, the radius of their star.
This activity assesses the fourth learning objective: Mathematically
analysing results to conclude properties of an exoplanet.
17
Pupils can then compare the diameter of their exoplanet with that of the
Earth and Jupiter, to get an idea of the size of their exoplanet.
18
We have seen how astronomers detect exoplanets and how they use the
results to find out what they are like. By August 2013, 929 exoplanets
have been discovered and more are being found all the time.
46-50
mins
Linking practical and
results to the big
question: are we
alone?
Plenary
19
N/A
There’s one in particular that made the headlines in 2011. It is a planet
orbiting the star Kepler-22, which is 620 light years away, near the
constellation Cygnus the swan. Kepler-22 is a star that is the same size,
mass and temperature as the Sun.
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Using the same method you have used today, astronomers detected an
exoplanet planet around this star (the planet is called Kepler-22b). They
calculated that this planet is only twice the size of Earth and it orbits its
star at the same distance that the Earth orbits the Sun.
Are we alone in the universe? What do you think?
20
Please note that with current technology it would be impossible to image
Kepler-22b and make out the planet’s surface. However, with new big
telescopes it will soon be possible to detect the presence of oxygen or
water in the planet’s atmosphere. If found, these could be key indicators
of life.
50-70
mins
Extension
activity
(optional)
21-24
Set of questions
which ask pupils to
evaluate their
analysis.
These questions assess the final learning objective: Evaluating analysis
method to identify underlying assumptions and their potential impacts on
the conclusions.
Students could write, or verbally discuss their answers to these questions.
Higher: These questions could be
provided to pupils who finish the
previous activities more quickly.
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Practical Instructions
This practical simulates the transit method of detecting an exoplanet orbiting a star. Pupils will
measure their ‘star light’, looking for a regular dip when their ‘exoplanet’ passes in front of their
‘star’. Their results will be in the form of a lightcurve, showing a regular drop in light.
We recommend group sizes of three or four for this practical, though this obviously depends on
equipment availability and the nature of the group.
Equipment needed:
 Light level sensor, preferably connected
to a data logger
 Bulb, preferably with diffusing globe (see
picture to the right)
 Ball attached to string
 Retort stand, bosshead and clamp
 Stopwatch (if not using data logger)
Method for setting up:
1. Connect the light level sensor to the datalogger (if used).
2. Point the light level sensor at the lamp.
3. Attach the string to the clamp, such that the ball is free to swing in circles.
4. Place the clamp directly over the lamp, so that the ball circles around the lamp.
5. Adjust the height of the clamp so that the ball passes in between the lamp and the light
sensor (see picture below).
Using different sized balls and
different lengths of string will
generate a variety of results across
the class.
Pupils should be instructed to pull the
ball outwards, until the string is taut,
then drop the ball, so it swings with a
regular circular motion. Pupils should
take their readings before the ball
slows down too much, due to air
resistance.
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
It may be necessary to turn off the classroom lights and/or draw the curtains to reduce the ambient
light level when readings are being taken. If you are doing this, please make sure you are aware of
the health and safety implications and take all necessary precautions.
Reading the data
If using data-logging software, the lightcurve created should show a periodic dip in light levels, like
the one below10. Pupils can read the time taken for one orbit along the x-axis (red arrow). The period
for the example below would be around 2.2 seconds.
Pupils can then read the fraction of light received from the star when the exoplanet is in the way
from the y-axis (green arrow). From this, they can calculate B, the fraction of light blocked by their
exoplanet. In the example below, the fraction of light still detected when the exoplanet is in front of
the star is 0.995. Therefore, B = 0.005.
Pupils will probably find their planets are much larger than Jupiter since the Sun is 10 times wider
than Jupiter, yet the lamps used in the experiment may not be 10 times wider than the balls. This
goes to illustrate that it is a lot easier to find larger exoplanets (e.g. ones larger than Jupiter) than
exoplanets that are smaller (for example, Earth sized).
Time (seconds)
If not using data-logging software, pupils will need to manually time the number of seconds between
each dip in the light using a stopwatch. They will also need to record the light levels displayed on the
sensor at normal levels and during a dip. Repeat readings should be taken and an average calculated.
10
Image taken from http://exoplanetmusings.files.wordpress.com/2011/12/00009a.jpg
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Using the supplied results
The supplied results come from real astronomical data taken by NASA’s Kepler space telescope11.
The star observed is Kepler-22 and the dip in the star’s light is caused by the planet Kepler-22b
passing in front of the star and blocking a small portion of its light. This is the same star and planet as
mentioned in slides 18-20 of the presentation.
Pupils should notice the large spread in readings on the original data (below). This is due to random
errors in the measurements, such as dust in interstellar space blocking some of the starlight.
Pupils should first use the corrected data on side A (below) to read off the time interval between
each dip in the star’s light. This is marked by the red triangles. This is how long it takes for Kepler22b to complete one orbit. Pupils should find the time for one orbit (T) to be around 290 days.
Pupils should then use the zoomed-in data on side B (below). The graph shows combined data from
the three dips observed from side A. Pupils should read off the fraction of starlight detected when
the exoplanet passes in front of the star. This is around 0.9995. Therefore the fraction of starlight
blocked by the exoplanet (B) is around 0.0005.
11
Data taken from http://kepler.nasa.gov/Mission/discoveries/kepler22b/
Jodrell Bank Discovery Centre
Big Science: Big Telescopes
www.jodrellbank.net
Additional resources on big telescopes

Full 50 minute documentary about current big optical telescopes
http://www.youtube.com/watch?v=QeobrudynUE

Square Kilometre Array Official Animations http://www.skatelescope.org/mediaoutreach/videos/

More information about current and future big telescopes, including school resources
http://www.bigtelescopes.org.uk/

Star Gazing Live video demonstrating how to make your own small telescope
http://www.bbc.co.uk/programmes/p00n6zkf
Use of Images
All images used in this lesson's presentation have been released under a creative commons license.
Every effort has been made to credit all images used. Where images do not display credits, this is
because this information could not be found. If you believe an image has been used incorrectly or
has been mis-credited, please email Jamie Sloan on the address shown below and I will be happy to
amend the presentation.
jamie.sloan@manchester.ac.uk