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Communicating Astronomy 101 School – CAP 2010
Cape Town, South Africa, 10 – 12 March 2010
Communicating Astronomy 101 School – CAP 2010
Build a Solar Viewer Activity
The aim of this activity is to show students how to build a solar viewer that will allow them to safely
view a projected image of the Sun, and allow them to safely track sunspots and watch eclipses. Note:
Do make it clear to learners never to look directly at the Sun under any circumstances, since it will
cause permanent and irreparable damage to their sight. They can, however, observe what is happening
to the Sun through a solar viewer, as described here.
Materials required
Two pieces of (not too thick) white cardboard
Aluminium foil
A pair of scissors
A pin
Some cellotape
Binoculars or telescope (optional)
1. Cut a five centimetre square in the centre of one piece of card.
2. Use a piece of aluminium foil to cover the square hole and tape to the card. Pierce a small hole
in the centre of the foil using a pin or the sharp end of a pencil.
3. Stand with your back to the Sun and hold the card with aluminium foil above your shoulder or
to your side, in the direction of the Sun. Use the other piece of cardboard to show the light
passing through the hole in the aluminium foil.
4. By changing the distance between the two pieces of card you can change the size and brightness
of the Sun's image.
5. Holding the two pieces of card approximately one metre apart works best.
An alternative
An alternative is to use a telescope or pair of binoculars to project an image of the Sun. How you can
use binoculars to produce a projected image of the Sun. At no time should you look through the
binoculars or telescope to view the Sun. If you use binoculars attach them to a tripod and cover one
lens with a piece of card. Aim the binoculars or telescope at the Sun and project the image on to a
screen or wall. To protect the binoculars or telescope from becoming hot and overheating, turn them/it
away from the Sun every minute or so.
This document is a modified version of the CSIRO (Australia) online “Build a Solar Viewer” activity
Communicating Astronomy 101 School – CAP 2010
Things to discuss with learners
Show the learners the simple ray diagram, like the one below, showing how the viewer works. Ask
them to explain or think about why the image gets larger (and fainter) when moving the cards further
away from each other., and the opposite when moving them closer.
If any sunspots are visible, the students can make simple picture of the position of the sunspots every
second day. Ask students to try to estimate the rotation rate of the Sun by watching the sunspots move
across the Sun.
Discuss with students what sunspots are, and why they appear darker than the rest of the Sun.
To the Sun
Image of Sun
This document is a modified version of the CSIRO (Australia) online “Build a Solar Viewer” activity
Communicating Astronomy 101 School – CAP 2010
Curved Space Demonstration
The aim of this activity is to demonstrate Einstein’s interpretation of gravity as a curve in space-time
around a massive object rather than as a force. The stronger the gravity (larger the mass) the more
space-time is warped. The idea is to demonstrate in 3D what is actually a 4D problem! In this
demonstration 3D space-time is represented by a 2D surface of stretchable fabric. By placing a heavy
mass on the surface of the fabric students will see how the fabric is distorted or curved by the mass in
the same way that space-time is curved by mass. This curvature will have an effect on other objects
placed on the fabric. Objects travelling on the surface of the fabric will follow the the curve in the
Materials required
A Hula Hoop
Lycra material (enough to cover the hula hoop)
Heavy ball (maybe from a boules set, or a really big heavy marble)
Tennis ball
Ping pong ball
1. Stretch the lycra material across the hula hoop and firmly attach it around the edge of the hula
hoop (sewing or stapling) so that you are left with circular flat surface of lycra.
2. Have two people hold the hula hoop steady horizontally so that you can look down at the
3. Place a heavy ball in the middle of the fabric, and note how the fabric is curved.
4. Place various balls at rest on the surface at the edge and note what happens to them.
5. Place various balls on the surface, with some initial speed perpendicular to the radius of the hula
hoop. Describe what happens to their direction of travel. (You should see the balls “orbiting” the
central mass).
Communicating Astronomy 101 School – CAP 2010
Density and Composition of the planets
The aim of this activity is to provide students with an idea of how planetary scientists deduce the
compositions of planetary bodies via measurements of their size and mass (and hence density).
Students will have the opportunity to measure the density of a variety of common materials, and to
compare these values with those found for the planets to deduce what type of materials the planets are
composed of.
Materials required
A piece of iron or steel, aluminium and some pieces of rock
Weighing scales
A graduated cylinder or beaker, large enough to hold the rock/metal samples
Water and a water container (a jug is fine)
Calculators, pens
1. Measure the mass of two pieces of metal and two pieces of rock.
2. Measure the volume of the samples by placing them in a beaker or cyclinder of water and
watching how much the water level rises.
3. Calculate the density of each sample using the formula: Density = Mass / Volume.
4. Calculate the densities of the planets from the mass and volume information provided in the
5. Compare the density values you get for each of the planets with those from the rocks/metals to
deduce what sort of materials the planets are made from.
Communicating Astronomy 101 School – CAP 2010
Hint: As a rule of thumb, gaseous or icy materials have densities about the same as water, rocky materials about 2-3 times the density of water, and metallic materials about 7 to 9 times the density of water.
Intermediate densities indicate mixtures of materials.
3.30 x 1023
6.083 x 1019
4.87 x 1024
9.284 x 1020
5.97 x 1024
1.083 x 1021
6.42 x 1023
1.631 x 1020
1.90 x 1027
1.431 x 1024
5.68 x 1026
8.271 x 1023
8.68 x 1025
6.833 x 1022
1.02 x 1026
6.254 x 1022
1.30 x 1022
7.150 x 1018
Questions (for learners to answer)
1. What do you notice about the distribution of densities of the planets and Pluto?
2. Which planets / dwarf planet would float on water?
Communicating Astronomy 101 School – CAP 2010
Determining the Angular Diameter
of the Sun Activity
In this activity the reflected image of the Sun is used to observe the Earth's rotation and to measure the
angular diameter of the Sun. Note: Do make it clear to learners never to look directly at the Sun under
any circumstances, since it will cause permanent and irreparable damage to their sight.
Materials required
● A 2-litre bottle
● 1 small piece of plexiglass mirror (less than 0.5 cm x 0.5 cm)
● A stand to keep the bottle from rolling, any of the following will work: 4" x 4" x 8" piece of
wood with a 1" deep 90 degree channel cut into one of the 4" x 8" faces OR the bottom part of
an empty egg carton OR a pair of bricks OR a pair of large books
● Epoxy or hot glue
● Water
● Sturdy white viewing screen (foam core or poster board)
● Watch with a second hand or a stopwatch
● Pencil
1. Make sure your stand will prevent the cylinder of the bottle from rolling. Epoxy or hot glue the
mirror near the middle of the bottle, along the length of the cylinder. Allow time for the glue to
set. Fill the bottle with water before using it. (See Figure 1as an example).
2. Take the bottle with the mirror and its stand outside along with the screen, the watch, and a
pencil. Never look directly at the Sun! Locate the Sun in the sky, and place the bottle on its
stand so that the mirror directly faces the Sun.
3. Place the viewing screen several metres away from the mirror, facing the mirror. You may need
a partner to hold the viewing screen in place. Rotate the cylinder so that an image of the Sun
appears on the screen. You will get the best results when the mirror is perpendicular to the Sun's
rays, and the viewing screen is parallel to the mirror. (This is easier to achieve when the Sun is
closer to the horizon. Also try this at different times of day and different times of year.)
4. Observe the image of the Sun on the screen. What do you notice?
5. Trace the image of the Sun on the viewing screen, and start timing. Stop timing when the image
of the sun has moved completely out of the circle you have traced. Try this several times. Vary
the size of the image and time it again. What do you notice?
This document is a modified version of the online “Reflections of a Star” activity
Communicating Astronomy 101 School – CAP 2010
The tiny mirror is reflecting light from the Sun and producing an image of the Sun on the screen. There
are two similar triangles in this experiment. One is an isosceles triangle whose base is the diameter of
the Sun, and whose congruent sides are rays coming from each side of the Sun's diameter toward your
mirror. The base of the second triangle is the diameter of the Sun's image on the screen. Its congruent
sides are rays coming from the mirror. Since these are similar triangles, the angular diameter of the
image on the screen is the same as the angular diameter of the Sun in the sky.
The Earth's spinning causes the image of the Sun to appear to move across the screen. What is the
angular velocity of the Earth's spin? If the Earth spins 360 degrees per 24 hours, then it spins 15
degrees per hour or 0.25 degrees per minute. The time it takes for the Sun's image to move "one sun
diameter" is about 2 minutes. For larger or smaller images, the time will be constant, as it is a measure
of another constant, the spin of the Earth. The angular diameter of the Sun can be found using a
15 degrees/60 minutes = x degrees/2 minutes
During periods of sunspot activity, you can safely observe sunspots this way. Remembering that this is
a reflected image, can you find the location of the sunspots on the sun based on what you see on its
Figure 1
This document is a modified version of the online “Reflections of a Star” activity
Communicating Astronomy 101 School – CAP 2010
Making Craters Activity
By making observations of craters, scientists can gain information about the size and mass of the
objects that strike a surface. You can practice these skills by doing this activity.
Materials required
A large tray or shallow pan, such as a cookie sheet
Dark sand
Flour, sugar, or another white powdered material
A collection of "meteorites": small objects of different sizes, shapes, and masses (e.g. marbles,
stones, balls, etc.)
A balance scale to measure the mass of each object
A ruler
Graph paper
Step ladder (optional)
1. On a separate sheet of paper, create a chart like the one overleaf and record all your data on the
chart to make comparisons.
2. Fill the tray with sand. Sprinkle a thin layer of flour over the top of the sand. The flour will
make it easier for you to observe the features of your crater.
3. Select a "meteorite" to drop onto your surface. Measure the mass and diameter or width of the
object and record your data on the chart.
4. Measure the height from which the meteorite will be dropped.
5. Drop the meteorite onto the surface. Carefully remove it and measure the size and depth of the
crater. Measure the distance between the crater and the furthest particles of sand or flour that
were thrown out of the crater with the impact of the meteorite.
6. On the graph paper, create a map of the location of each crater. Number the craters according to
the sequence in which they were created.
7. Repeat steps 2 – 5, with different starting heights and using other objects, until you have created
several craters. Try dropping or tossing a few meteorites at an angle rather than straight down
onto the surface.
This document is a modified version of the NOVA Online classroom activity called “Doomsday Asteroid”
Communicating Astronomy 101 School – CAP 2010
Width of
Mass of
Height or
angle from
meteorite is
Shape of
Diameter of
Depth of
Distance of
Questions (for learners to answer)
Answer the following on a separate sheet
1. How can you tell which craters were formed first or last?
2. What variables affect the shape and size of the crater?
3. What features are different between craters formed by a meteorite that falls straight down and a
meteorite that strikes at an angle?
4. What features are similar among all the craters?
5. Carefully exchange your tray of sand with another group and analyze the craters in the tray you
receive. Which craters seem to be oldest? Which seem to be youngest? What evidence can you
find about the size and mass of the meteorites? Which craters were formed by meteorites that
struck at an angle? After you have investigated the other group's craters, exchange graph paper
so that you can check your analysis.
This document is a modified version of the NOVA Online classroom activity called “Doomsday Asteroid”
Communicating Astronomy 101 School – CAP 2010
The Outer Atmosphere Ejection during a
Supernova Explosion Demonstration
The aim of this activity is to demonstrate how the outer layers of a star are ejected during a supernova
explosion. In this demonstration the basketball represents the outer part of the core of the star and the
tennis ball represents the atmospheric layers of the star. When the core of the star implodes it contracts
catastrophically. At the end of the contraction the material in the core comes together with such a large
amount of force that it rebounds. As the core contracts, all the outer atmospheric layers are also
contracting and following the core. They are less dense and take a little longer to contract than the core.
When the core (basketball) rebounds, the atmospheric layers (tennis ball) are still in-falling towards the
core. The rebounding core meets the incoming atmospheric layers with enough energy to literally blow
the atmospheric layers away from the star due to the transfer of momentum from the basketball to the
tennis ball. This is the supernova explosion.
Materials required
● Tennis ball
● Basket ball or a football
1. First drop the tennis ball and basketball individually on the floor to see how far above the floor
the basketball and the tennis ball rebound.
2. Then place the tennis ball on top of the basketball and hold them out in front of you.
3. Let go of both balls at the same time so that they fall towards the floor together.
4. When the two balls hit the floor the tennis ball will suddenly rebound with enough energy to hit
the ceiling!
Based on Chandra webpage
Communicating Astronomy 101 School – CAP 2010
The 30 m Solar System Activity
The aim of this demonstrations is to demonstrate the relative sizes and distances between the planets
and the Sun in our solar system. It is also key to point out that the planets orbit the Sun. This activity is
ideally conducted outside, as it requires a lot of space. It may also be nice to highlight one interesting
fact about each solar system body. For older children you may wish to get them to calculate the scaled
down sizes and distances. We do not do this in this example.
Solar system body
Actual diameter
Scaled Diameter
Actual distance
from Sun
Scaled distance
from Sun
(the dwarf planet!)
Materials required
● 10 markers for the Sun, each planet and Pluto
● A piece of card (ideally laminated) with a color photo of each body to be attached to each
marker. Also have a scaled drawing of each body next to the photo, showing the scaled size of
the body (these may actually be dots, or not even visible)
● Measuring tape for measuring out distances for the marker positions
● Blue tac (or Prestik) to attachcard to the markers
Communicating Astronomy 101 School – CAP 2010
1. Explain to the students what the aim of the activity is: to illustrate the relative sizes and
distances between the Sun, planets and Pluto. This activity is ideally conducted with 2-3
students per marker, with the markers placed along a straight line. Determine ahead of time
where to position the Sun’s marker so as to have enough space to position all the other markers.
2. Position the Sun’s marker and attach the picture card.
3. Have students measure the correct distance to Mercury from the Sun’s marker position. Have
them place their marker down at the correct position and attach the appropriate card.
4. Repeat for all the other planets and Pluto.
5. Explain the criteria needed for an object to be classified as a planet and explain why Pluto has
been downgraded to a “dwarf planet” classification.
Communicating Astronomy 101 School – CAP 2010
The Parallax Activity
In this activity students investigate the relationship between the parallax and distance. Parallax is one of
the most fundamental methods astronomers use to establish the distance scale in the Universe. This
activity needs at least 2 students performing it.
Materials required
A small thin pencil or stick
Two metre sticks
A small table or barstool
A large black (or white) board with some chalk (white board) markers
Some clear cellotape
1. Tape one metre stick horizontally on to the small table (or barstool) securely, with measuring
ticks face up.
2. Place this table (or barstool) a few meters away from the black (or white) board, with the 1m
mark of the meter stick pointing perpendicular to the board.
3. Place the small pencil at the 25cm mark.
4. Ask one student. To look directly along the meter stick towards the black (white) board. Ask the
student to close his left eye, and then his right. Ask the student what does she/he notice about
the position of the pencil.
5. Ask the student to only close his left eye. Then ask the second student to make a mark on the
black (white board) of the position the pencil, as seen by the first student. The chalk (or white
board marker) can be used for this. This might be a bit tricky at first, but let the students play
around with it a bit.
6. Then ask the first student only close his right eye. Now ask the second student to make a second
mark at the position of the pencil, as seen by the first student.
7. Ask the second student to measure the distance between the two marks, using the second metre
stick and record the measurement on a piece of paper.
8. Ask the students to repeat steps 4 to 7, placing the pencil at the 50 cm, 75cm and 1 m marks.
9. Ask students to calculate the relative shift (= amount pencil appears to shift ÷ amount pencil
appears to shift when at 25 cm) and record their results in the table below.
Communicating Astronomy 101 School – CAP 2010
Position of Pencil (in cm)
Parallax (relative shift)
Questions (for learners to consider)
Ask students to imagine the pencil moving further and further away, and to express their thoughts as to
the usefulness of parallax as the distance increases.
Show them a diagram, such as the one below, which illustrates how astronomers use to parallax to
calculate the distance to stars. Then explain to them what a light year is (distance light travels in one
year = 9.5 x 1012 km). Then ask them to calculate how small the parallax angle would be for a star that
is 4 light-years (about the distance to the closest star) given that the Sun-Earth distance is about 150
million km.
Communicating Astronomy 101 School – CAP 2010
The Rocket Launch Activity
The aim of this demonstration is to illustrate the principle of rocketry. This activity will use the water
rocket modules from the S.A.A.O. The activity can be used in groups of 4 or so, depending on how
many rocket modules you have and how many launches you care to do! Have fun!
Materials required
● A few 2 litre plastic bottles
● S.A.A.O rocket launcher module with attached pump
● Ample supplies of water
1. First do 2-3 rocket test launches. Fill the 2 litre bottles with various amounts of water (maybe ¼,
½ and ¾ of the bottle). Check also with an empty bottle and full bottle.
2. Hold the bottle rocket gently with second and third finger against the mouth of the bottle (this is
to avoid loss of water).
3. Plug it upside down into the launcher.
4. Connect the pump to the launcher when the bottle rocket is steady.
5. Starting pumping, see what happens to the bottle rocket: Why does it happen?
Questions (for learners to consider)
1. What forces are acting on the rocket while on transit.
2. Is the weight of the rocket constant? Explain.
3. What factors influence the maximum height reached?
4. Explain how you could increase the height reached by the rocket.
Communicating Astronomy 101 School – CAP 2010
The Universal Expansion Activity
The aim of this demonstration is to illustrate how galaxies are moving apart from one and other in all
directions as the Universe expands. The discovery of the expansion of the Universe was made in 1929,
when astronomer Edwin Hubble observed that galaxies are moving away from the Earth. He also found
that the speed of recession was proportional to their distance. Hubble realised that this actually implied
that all galaxies are moving away from each other, and not just from the Earth. The movement of the
galaxies is not actually through space but is due to the expansion of space itself between the galaxies.
This activity can be done in groups of around four or less.
Materials required
A balloon
Binder clip
Tape measure, or string with a metre stick
Permanent marker
1. Inflate the balloon to about 40cm circumference (grapefruit size).
2. Roll the neck of the balloon and clamp it using the binder clip to stop air escaping.
3. Using a permanent marker mark a point near the equator of the balloon. Label this H for home.
4. Starting from H, measure 1cm intervals along the balloon’s equator, marking five distinct
points. Label these points 1-5.
5. Measure the distances from H to each point, and record the values.
6. Inflate the balloon further to a circumference of about 60cm and clamp the neck.
7. Describe what happens to the points.
8. Re-measure the distances from H to each point and record the values.
9. Calculate the distance that each point has moved.
Based on NASA guide
Communicating Astronomy 101 School – CAP 2010
Original distance from
Final distance from
Distance travelled
Question (for learners to consider)
What do you notice about the relationship between the distance travelled and the original distance from
Based on NASA guide