Pre and post-visit activities Our Earth, Sun and seasons
Vocabulary List
Pre-visit Adult Education at Scienceworks
Activity 1: A model of the Earth and Moon
Activity 2: Day and night on Earth
Activity 3: Diurnal motion
Activity 4: Reasons for the seasons
Activity 5: A model showing the path of the Sun
Post-visit
Activity 6: Science and the seasons (Certificate I)
Activity 7: Some days are really longer than others (Certificate II)
Activity 8: The angle of light makes a difference
Activity 9: People shadows
Activity 10: Using shadows to tell the time
Activity 11: Making your own equatorial sundial
Activity 12: Researching the seasons and culture
Our Earth, Sun and seasons
These activities are designed to familiarise Certificate I and II students with the concepts and vocabulary
they will encounter when they visit Scienceworks to see the Spinning Out planetarium show, and to
reinforce and extend their knowledge afterwards.
You may need to modify or extend some of the ideas presented to best suit the needs of your students
or student groups. Students should become familiar with the following words and their meanings,
particularly those used in the planetarium show synopsis and on-site activities, before they visit
Scienceworks.
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Vocabulary list - Our Earth, Sun and seasons
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Our Earth, Sun and seasons
Words
Activities
Words
Activities
constellation
(in) contrast
convinced
extreme
orbit
remote property
roughly (six months)
transforms
use her imagination
zodiac
Show
Synopsis
correspond
Activity 6
absorbed
combined
motion
reflected
Activity 7
cast, casts a shadow
Activity 8
casts a shadow
give some indication of
Activity 9
diameter
elliptical
relative sizes
Activity 1
Activity 10
axis
illuminate
imaginary line
simulate
rotate
tilted
with reference to
Activity 2
diurnal
rotation
Activity 3
decrease
hemisphere
increase
intense, intensity
simulates
the source
Activity 4
altitude
ancient
axis
cast shadows
compensate
dial
ecliptic
elliptical
equinox
face
gnomon
occurs
originated
outskirts
referred to; zero reference
solstice
tilted
universal
apparent path
equinox
solstice
Activity 5
benefit mankind
Activity 11
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Activity 1: A model of the Earth and
Moon
Background information
This activity demonstrates the relative sizes of the Earth and Moon, and the
distance between them. The Moon is our nearest neighbour. It orbits the Earth
following an elliptical path and therefore the distance between the Moon and the
Earth varies from about 350 000 km to 400 000 km. On average the Moon is
385 000 km away and while this at first seems like a large distance, the Moon is
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very close to Earth compared to the planets in our Solar System. The diameter of
the Moon is about 3 500km which means that the face of the Moon is roughly the
same breadth as Australia. The Earth has a diameter of approximately 12 800 km.
The Moon is a little less than a quarter the diameter and approximately one-fiftieth
the volume of the Earth.
What you need
•
a handful of modelling clay, plasticine or play-dough
•
ruler
•
calculator
What you do
Part A – Estimating the relative size of the Earth and the Moon
1.
Collect a hand f ul of c l a y.
2.
D ivide the c l ay into t wo balls ( or s phe r es ) s o that one represents
the s i ze of the Moon when c o m pa r ed to the other ball whi c h represents the
Our Earth, Sun and seasons
s i ze of the Ea r th ( no hint s allowed ) .
3.
Co mm ent on the di ff e r en c es of the m odel s ea c h g r oup
has m ade.
4.
R e c o m bine the t wo balls or s phe r es into one lu m p of c l ay again.
5.
D ivide the lu m p of c l ay into 50 pie c es of app r o x i m ately equal s i ze.
6.
C hoo s e one pie c e then r e c o m bine the other 49 into a s i ngle c hun k .
7.
R oll ea c h pie c e into the s hape of a ball s o that they end up wi th t wo
spheres.
You now have an app r o x i m ate sc ale m odel of the Ea r th and
the Moon, with the small ball (made of one piece) representing the Moon and the
large ball (made of 49 pieces) representing the Earth.
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P a r t B – E s tim a ting the di s t a n c e b e t w ee n the E a r t h a nd the M oon
8.
P r edi c t how f ar apa r t their m odel Moon and Ea r t h s hould
be to represent the Moon-Earth distance.
9.
H old the Moon up to the Ea r t h and t r y to vi s uali s e how
f ar a way the Moon s hould be. When you r ea c h a agreement , then
m ea s u r e th e di s t an c e.
10.
Note: T he a c tual Moon - Ea r t h s epa r ation is about 30
Earth diameters.
11.
C al c ulate how long this di s t an c e would be in your m odel and
and pla c e your Moon at that di s t an c e.
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Our Earth, Sun and seasons
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Activity 2: Day and night on Earth
Background information
It takes the Earth approximately 24 hours to spin once on its axis. The Earth’s axis
can be thought of as an imaginary line that runs through the North and South Poles.
The Earth’s axis is tilted 23.5 degrees to the vertical. As the Earth turns, half the
Earth faces the Sun and experiences day-time and half is in shadow and
experiences night-time. The line that separates day and night is called the
terminator . The imaginary line that separates the Northern Hemisphere and the
Southern Hemisphere is called the Equator.
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Our Earth, Sun and seasons
The time it takes for the Earth to spin around once with reference to a distant star is
called a sidereal day and is always 23 hours, 56 minutes and four seconds long. This
means that the star Sirius for example would return to the same position in our sky after
23 hours, 56 minutes and four seconds. The length of a solar day measures day length
with reference to the Sun. The solar day can vary depending on where you are on Earth
and the time of year. On average, the solar day is about four minutes longer than a
sidereal day. This is because as the Earth turns on its axis, it also moves around the Sun.
During summer at the South Pole the Sun circles the sky and never sets. It is daytime continuously for (approximately) six months. During winter the Sun never rises
and it is constant night-time for (approximately) the next six months.
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The following activity uses a model to simulate day and night as the Earth rotates
on its axis. The questions help the students identify the terminator and understand
how day occurs at different times depending on where you live on Earth. The
activity follows a teacher demonstration using a globe of the Earth to help the
students.
Teacher Demonstration
What you need
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•
globe of the Earth
•
Blu Tak
•
small cardboard figures
•
lamp without shade
•
access to a darkened space
What you do
1.
In a darkened room turn on the shadeless lamp and illuminate the globe.
Identify the lit and unlit sides of the globe.
2.
Ask the students to point out the countries experiencing day and those
experiencing night.
3.
Using Blu Tak attach three small cardboard figures to the globe; one on
Australia, one on Greece and one on Malaysia for example. Ask the
students to watch their shadows change as the Earth rotates. (i.e sunrise,
noon, sunset and night). Ask the students to watch the Australian figure and
to call out the part of the day it is experiencing as the Earth rotates. What is
the Greek figure experiencing whilst the Australian is experiencing morning?
Our Earth, Sun and seasons
4.
Identify the north, south, east and west directions. Stick labels on the walls
if necessary.
5.
Demonstrate the movement of the Earth from west to east.
6.
Identify the ‘terminator’ – the imaginary line that separates day and night.
7.
Model the rotation of the Earth that represents one solar day (24 hours).
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Student Activity
What you need
•
polystyrene ball
•
ice-cream stick or skewer
•
torch
•
pen
•
globe
What you do
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1.
The polystyrene ball is used to represent the Earth. Mark the ball with a
broken line dividing the ball in half. This line will represent the equator.
2.
Mark in the position of Australia, Melbourne and Perth with a
pen. (The globe can be used for reference.)
3.
Identify north, south, east and west.
4.
Push the ice-cream stick through the polystyrene ball to represent the
imaginary axis running through the North and South Pole.
5.
Get help and show the direction the Earth turns (from west to east)
with the axis slightly tilted.
6.
Switch the torches on while the room is darkened. Now simulate the Earth
turning with your model and try to answer the following questions.
Questions
1.
What happens to the shadow across Australia when Earth turns once?
2.
Find the terminator . What is it and how does it move?
3.
Who experiences day-time first, Melbourne or Perth?
Our Earth, Sun and seasons
Optional
Ensure the model has a tilt.
4.
Look down on your model from the North Pole and turn the Earth once.
What do you notice about the day-time and night-time here?
5.
Look up on your model from the South Pole and turn the Earth once.
What do you notice about the day-time and night-time here?
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Activity 3: Diurnal motion
Background information
The Earth spins once every 24 hours resulting in day and night. This rotation
causes the stars, (including the Sun), to appear to rise in the east and set in the
west. Some stars travel in a large arc across the sky, then disappear below the
horizon. Other stars never ‘set’ below the horizon but trace a circle in the sky. The
centre of these circles is a point called the South Celestial Pole. This part of the sky
is directly above the South Pole of our Earth. That is, if you stood at the South Pole,
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the South Celestial Pole would be directly overhead and the stars would seem to be
rotating clockwise around this point. In Melbourne, the South Celestial Pole is at an
angle of (approximately) 38 degrees, Melbourne’s latitude. From southern Australia,
stars like those that make up the Southern Cross, never set but are always visible in
our sky and can be seen rotating around the South Celestial Pole.
Teacher demonstration
What you need
•
black umbrella
•
white circular stickers
What you do
1.
Open up a black umbrella
2.
On the inside of the umbrella, label or identify the centre or turning point of
the umbrella (above the shaft) which will model the South Celestial Pole.
3.
Stick the white circular stickers in the appropriate positions to represent the
Our Earth, Sun and seasons
Southern Cross and the star Canopus as shown in the diagram below.
These stars are always above the horizon in Southern Australia throughout
the year. (Refer to the diagram.)
4.
Hold the umbrella at approximately 38 degrees to the horizontal and turn the
umbrella once slowly in a clockwise direction. This models diurnal motion
from Southern Australia (24 hours).
5.
Hold the umbrella so that the South Celestial Pole is directly above your
head. Turn the umbrella once slowly. This models diurnal motion at the
South Pole for one day (24 hours).
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Student Activity
What you need
•
polystyrene ball
•
ice-cream stick or skewer
•
torch
•
pen
•
globe
What you do
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1.
The polystyrene ball is used to represent the Earth. Mark the ball with a
broken line dividing the ball in half. This line will represent the equator.
2.
Mark in the position of Australia, Melbourne and Perth with a
pen. (The globe can be used for reference.)
3.
Identify north, south, east and west.
4.
Push the ice-cream stick through the polystyrene ball to represent the
imaginary axis running through the North and South Pole.
5.
Get help and show the direction the Earth turns (from west to east)
with the axis slightly tilted.
6.
Switch the torches on while the room is darkened. Now simulate the Earth
turning with your model and try to answer the following questions.
Questions
1.
What happens to the shadow across Australia when Earth turns once?
2.
Find the terminator . What is it and how does it move?
3.
Who experiences day-time first, Melbourne or Perth?
Our Earth, Sun and seasons
Optional
Ensure the model has a tilt.
4.
Look down on your model from the North Pole and turn the Earth once.
What do you notice about the day-time and night-time here?
5.
Look up on your model from the South Pole and turn the Earth once.
What do you notice about the day-time and night-time here?
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Activity 4: Reasons for the seasons on
Earth
Background information
The Earth orbits the Sun in a slightly elliptical path. This means that sometimes the
Earth is slightly closer to the Sun than other times but this does not explain why we
have seasons. If this was the case then the north and south hemispheres would
experience the same seasons at the same time of the year. This does not happen.
When it is summer in the Northern Hemisphere, it is winter in the Southern
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Hemisphere (and vise-versa) and when it is autumn in the Northern Hemisphere it is
spring in the Southern Hemisphere (and vice-versa). The two hemispheres
experience opposite seasons.
The seasons are mainly caused by the Earth’s tilt. As the Earth travels around the
Sun, it remains tilted (23.5 degrees) in the same direction so that sometimes the top
half of the Earth is pointing toward the Sun while at times it points away. During our
summer, the Southern Hemisphere is tilted towards the Sun. Therefore light from
the Sun is more intense and is more effective at heating the ground than during
winter when the Sun’s rays are more spread out. The Sun is also in the sky longer
during summer allowing more time for warming and less time for cooling the Earth.
Half way between the times when the Earth is pointing toward or away from the
Sun, both hemispheres get almost equal amounts of sunlight. These times are what
we call spring and autumn.
The following activity simulates how the Earth orbits the Sun with its North Pole
always tilted at 23.5 degrees. It should be noted that the tilt of the Earth is the
Our Earth, Sun and seasons
reason that the north and south hemispheres experience opposite seasons.
What you need
•
balloon
•
felt tipped pen
•
straw
•
sticky tape
What you do
1.
Blow up a balloon to a diameter of approximately 25 cm. This will represent
the Earth.
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2.
With a felt tipped pen, mark the North Pole, South Pole, the position of
Australia, Europe and the Equator.
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3.
Cut the straw in half.
4.
Make three cuts on one end of the straw forming tabs. (See diagram)
5.
Stick this straw onto the balloon at the North Pole to represent an imaginary
axis.
6.
Repeat steps 4 and 5 to represent an imaginary axis at the South Pole.
7.
Choose a light source in the classroom that will represent the Sun.
8.
C i r c le the light s ou r c e wi th the m odel, k eeping the a x is
at the North Pole slightly tilted as they circle all the way around the source.
9.
Notice that s o m eti m es the top half of the Ea r t h is
pointing toward the Sun and sometimes it is pointing away.
10.
Model and discuss what would happen if the Earth circled the Sun straight
up and down with no tilt.
Our Earth, Sun and seasons
Optional
•
Identify the positions when it is summer, winter, autumn and spring in Australia.
Discuss why.
•
Identify the positions when it is summer, winter, autumn and spring in
Europe. Discuss why.
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Activity 5 : A Model sho wing the path
of the Sun
The following activity represents the apparent path of the Sun on four special
occasions of the year in the Southern Hemisphere.
•
Path (a) – Summer Solstice (December 22), when the Southern Hemisphere
has the longest day and shortest night of the year.
•
Path (b) – Autumn and Spring Equinox (March 22 and September 23), when the
Southern Hemisphere has the length of day and night approximately equal.
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•
Path (c) – Winter Solstice (June 22), when the Southern Hemisphere has the
shortest day and the longest night of the year.
What you need
•
A4 m a s t er c opy of m odel
•
cardboard
•
glue
•
protractor
•
pipe cleaners
•
sticky tape
•
stanley knife
What you do
1.
Reduce the size of the master copy of the model so that two models fit onto
one A4 sheet.
2.
Glue the A4 sheet onto cardboard.
3.
Carefully cut out the model along the dotted lines outlining path (a), (b) and
Our Earth, Sun and seasons
(c) using a stanley knife.
4.
Fold the ends of path (c) along the thick black lines so that it remains tilted
at an angle that approximates 28 degrees. You may want to use a protractor
to measure the angle.
5.
Fold the ends of path (b) along the thick black lines so that it remains tilted
at an angle that approximates 52 degrees. You may want to use a protractor
to measure the angle.
6.
Fold the ends of path (a) along the thick black lines so that it remains tilted
at an angle of approximately 75 degrees. You will need to wrap sticky-tape
around the ends of this path so that it is supported at this angle.
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A model showing the path of the sun
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Activity 6: Science and the seasons
Certificate I
What you need
• Research facilities
Question
1 How does knowledge and understanding about the seasons benefit mankind?
(eg. farming, gardening. etc.)
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Our Earth, Sun and seasons
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Activity 7 : Some days are really longer
than others
Background information
The shortest day of the year, the Winter Solstice, is around June 22. This day has the
least amount of daylight hours. The Sun rises in the north-east, stays low in the sky and
sets in the north-west. The longest day of the year, the Summer Solstice, is around
December 22. This day has the greatest amount of daylight hours. The Sun rises in the
south-east, moves high into the sky, then sets in the south-west.
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The seasons in the Southern Hemisphere are:
•
Summer: December, January and February
•
Autumn: March, April and May
•
Winter: June, July and August
•
Spring: September, October and November
You can view a current colour map of the Earth showing the day and night regions at
http://www.fourmilab.ch/earthview/vplanet.html
What you need
•
pen and paper
•
sunrise and sunset times (for Melbourne), you can get these from a newspaper or
from the Melbourne Planetarium web site:
http://museumvictoria.com.au/Planetarium/
Our Earth, Sun and seasons
Note: sunrise and sunset times for any location in the world can be obtained from:
http://www.ga.gov.au/geodesy/astro/
What you do
1. Calculate the day length, in hours and minutes, of the Summer Solstice and the
Winter Solstice.
2. Now do the same for the days of the Equinoxes.
3. Calculate day length for some other days.
4. Discuss the path of the Sun at different times of the year.
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Optional
Ask student students to:
•
Calculate day length every fortnight for the year and draw a bar graph using this
information (Day length versus fortnight, primary students).
•
Calculate day length for every day of the year and graph this information using
excel (Day length versus day, secondary students).
Questions
1.
Describe the shape of the graph.
2.
How many weeks are there where the day length:
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3.
(i)
is below 12 hours?
(ii)
is more than 12 hours?
Does the graph correspond with the longest day being around December 22,
and the shortest being around June 22?
Our Earth, Sun and seasons
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Some days are really longer than others
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Questions
Our Earth, Sun and seasons
1.
Colour in the different sections of the graph showing the different seasons
in a year.
2.
Describe the shape of the graph.
3.
How does the amount of daylight in a day change from winter to summer?
4.
Cross out the wrong word in bold in the following sentences:
(i)
During summer, the days are longer and the nights are
longer/shorter in Australia.
(ii)
During winter, the days are shorter and the nights are
longer/shorter in Australia.
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Activity 8 : The angle of light makes a
difference (A)
Background information
When combined with the Earth’s motion around the Sun, the tilt of the Earth
(23.5 degrees) causes the seasons. There are two factors that work together to
make summer hot and winter cool. Firstly, during summer the Southern Hemisphere
is tilted towards the Sun. Therefore light from the Sun is more intense and is more
effective at heating the ground than during winter when the Sun’s rays are more
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spread out. Secondly, the Sun travels a longer path across the sky. It rises in the
south-east and sets in the south-west. This means that the Sun is in our sky longer,
reaching a higher altitude and therefore has more time to heat the ground and less
time for cooling it.
Approximate dates of the equinoxes and solstices in Melbourne.
Autumn
March 22
Equinox
Sun lies on the
day and night
Maximum
celestial equator
are equal in
altitude of the
– rises due east
length
Sun at
and sets due west
midday:
51 degrees
Winter Solstice
Spring Equinox
Our Earth, Sun and seasons
Summer
June 22
September 23
December 22
Solstice
Sun is furthest
shortest day,
Maximum
north – rises in
longest night
altitude of the
the north-east
Sun at
and sets in the
midday:
north-west
28 degrees
Sun lies on the
day and night
Maximum
celestial equator
are equal in
altitude of the
– rises due east
length
Sun at
and sets due
midday:
west
52 degrees
Sun is furthest
longest day,
Maximum
south – rises in
shortest night
altitude of the
the south-east
Sun at
and sets in the
midday:
south-west
75 degrees
The following activity deals with the first effect that causes the seasons, the
intensity of sunlight.
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As the Earth orbits the Sun, the angle of sunlight varies. This is modelled in the
activity using a torch and graph paper. Students will see that moving the torch at
different angles changes the surface area of the beam. Furthermore, since the
same amount of light is given off by the torch, an increase in surface area causes a
decrease in intensity.
In order to complete this activity a grasp of measuring surface area is required.
Surface area is the amount of two-dimensional space an object takes up. One way
of measuring it is by counting up squares on graph paper. If the units are 1cm x
2
1cm, then the unit of the surface area measured is centimetres squared or cm .
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2
Students can use graph paper to calculate surface area in cm . To simplify the
measurement of surface area for students, the surface area can be measured
by counting how many dots a certain space takes up.
Extension information
Seasons at the Equator and the Poles
The intensity of sunlight varies according to where you are on Earth. The Sun is
almost always directly overhead at the Equator. This means that light from the Sun
covers a small surface area. At other places further north or south of the Equator,
the angle of the Sun decreases, spreading the sunlight over a larger surface area.
The light also travels a greater distance through the atmosphere and more of the
light is absorbed or reflected before it reaches the ground. Places further north or
south of the Equator do not experience temperatures as hot as places closer to the
Equator. In addition, the Sun is always up for 12 hours at the Equator so generally
the year is divided into the wet season and the dry season.
The seasons are more extreme at the Poles. The North and South Poles experience
Our Earth, Sun and seasons
(almost) 6 months of continuous daylight followed by (almost) 6 months of
darkness. The Sun does not come up at the South Pole during the whole of winter.
At the South Pole, winter begins on March 22 and ends on September 23. The Sun
peeps up from the snow on September 23 and summer begins. At the North Pole
the opposite happens.
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What you need
•
A4 sheet of graph paper (or dotted paper)
•
torch
•
30 cm ruler
•
sticky tape
•
cardboard protractor
•
glue
What you do
1.
Stick the outline of the protractor (provided) onto cardboard and cut it out when
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it is dry.
2.
Lay a sheet of graph paper (or dotted paper) on a flat bench. Place the beam of
the torch 15cm along the ruler and fix it together with sticky tape. (Make sure
that the torch can be easily switched on and off once it is fixed to the ruler.)
3.
Stand the ruler, with torch attached, upright above the graph paper.
4.
Switch the beam on. Count the squares (or dots) that the beam covers at this
distance. Record this in a table. This angle represents the Sun’s rays at midday
at the Equator, when the Sun is directly overhead.
6.
Keeping the torch at this distance, move the ruler (with the torch attached) and
change the angle of the torch to 75 degrees. This angle represents the Sun’s
rays in mid-summer at midday in Melbourne.
7.
Count the squares (or dots) that the beam covers now. Record this value
in the table.
8.
Change the angle to 28 degrees and again count and record the number of
squares (or dots) the beam covers. This angle represents the Sun’s rays in
mid-winter at midday in Melbourne.
Our Earth, Sun and seasons
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The protractor
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Our Earth, Sun and seasons
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The angle of light makes a difference (B)
Introduction
The angle at which light is directed can affect how much heat is felt. In the following
activity, you will see how the brightness of the light changes when a torch shines on
paper at different angles. At the Equator, the Sun is almost always at 90 degrees (at
midday) all year round. In Melbourne, the Sun never reaches that high. The highest
angle that the Sun reaches in mid-summer at midday is 75 degrees. In spring and
autumn, the maximum altitude the Sun reaches is 52 degrees and in mid-winter, the
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Sun reaches only about 28 degrees.
Count how many dots or squares the light takes up at the different angles and
record your values in the table below.
(a)
(b)
(c)
Angle of torch
Representing the Sun
Surface area
at a distance of 15 cm
at midday
(number of dots or
squares)
90 degrees
Equator
75 degrees
mid-summer in Melbourne
52 degrees
mid-autumn/mid-spring in
Our Earth, Sun and seasons
Melbourne
28 degrees
mid-winter in
Melbourne
Questions
1.
How does the angle change the (surface area or) amount of space the beam
takes up on the paper?
2.
How does the activity demonstrate why it is easier to get sunburnt in
summer than in winter?
Optional
3.
Find out the altitude the Sun reaches at the North and South Pole during a
year.
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Activity 9 : People shadows
Background information
Our own shadows are created when our body blocks sunlight. Since the Sun
appears to move across the sky during the day, our shadows change shape.
The time of day when shadows are shortest is when the Sun is due north. Shadows
disappear all together when the Sun is directly overhead. In Melbourne the Sun is
never directly overhead. The only areas of Australia that have the Sun directly
overhead during the summer are north of the Tropic of Capricorn.
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What you need
•
coloured chalk
What you do
1.
G o out s i de to an open a s phalt/ c on c r ete a r ea. W o r k in
pai r s and ta k e it in tu r n to s tand in a S c a r e c r ow po s ition whil s t the
pa r tner t r a c es a r ound the s hadow u s ing c olou r ed c hal k .
2.
Pla c e a s i gn r eque s ting that no-one r ub s o f f the c halk
du r ing the day .
3.
Return to the same position just before lunch and again in the afternoon.
Ea c h ti m e the s tand in the s a m e po s ition and u s e a
di ff e r ent c olou r ed pie c e of c halk to t r a c e the s hado w. L abel the
different coloured shadows to indicate which shadow is cast in the morning
and which shadow was cast in the afternoon.
4.
Di sc u s s what happened to the s hado ws and list any s ugge s tions you
have to explain the different size and direction.
Our Earth, Sun and seasons
5.
You could r epeat this exercise f or c o m pa r i s on on other ( s unn y) da ys and
d i sc u ss your results .
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Activity 10 : Using shadows to tell the
time
Background information
Shadows were once used to give some indication of time using only a stick and its
shadow. The Sun is at its highest point in the sky around midday or the middle of
the day. This is when the casts the shortest shadow. When the Sun is close to the
horizon, it casts a long shadow.
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The maximum altitude of the Sun varies throughout the year. In Melbourne, the Sun
reaches a maximum altitude of 75 degrees in summer. The Sun rises in the southeast and sets in the south-west making the days long and the nights short. During
winter the Sun is much lower and the maximum altitude it reaches in Melbourne is
only 28 degrees. The Sun rises in the north-east and sets in the north-west and the
days are short while the nights are long.
Always ensure that students are warned never to look directly at the Sun.
What you need
•
access to an open asphalt or concrete area
•
watch
•
new pencils
•
large sheets of cartridge paper
•
plasticine
•
coloured chalk
Our Earth, Sun and seasons
What you do
1.
On the centre of a large piece of cartridge paper stand a pencil in a vertical
position using a piece of plasticine.
2.
Take the paper outside to an open asphalt/concrete area. Trace around the
edge of the paper and the base of the plasticine in case it moves out of
place. On each side of the paper write or draw an orientation landmark such
as shelter shed, playground etc. This will enable the students to return the
shadow stick to the same position for each reading.
3.
Every hour draw over the shadow of the pencil and mark the time. Continue
to mark the shadow every hour until 2.00pm. You should be able to have at
least five shadows marked (10am, 11am, 12pm, 1pm, 2pm).
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4.
At each reading note the position of the Sun using features in the
landscape. For example: at ten o’clock the Sun was just above the corner of
the shelter shed.
5.
After a few readings ask the students to predict the length and direction of
the next shadow.
6.
Repeat the s a m e a c tivity tomorrow . P r edi c t what you think might happen.
Di sc u s s how this c ould be u s ed as a c l o c k . How r eliable is it?
Try to e x plain why the s hado ws c hange.
7.
The Sun appea r s to m ove but in f a c t it is the Ea r t h that is m oving
not the Sun. ( R e f er ba c k to the globe a c tivity if you need a reminder. )
Our Earth, Sun and seasons
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Activity 11 : Making an equatorial sundial
Background information
Sundials have been used to tell the time by different societies for more than 5 000
years. The Greek historian Herodotus (484-425 BC) stated that sundials originated
with the ancient Chaldeans and Sumerians who lived in Iraq. They used vertical
rods on their buildings to cast shadows in order to tell the time and the date, and
were the first people to divide the day into 24 hours, the week into seven days and
the year into 12 months.
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There are many different types of sundials. The equatorial sundial is just one
example.
The equatorial sundial
The circular dial plate of the sundial lies parallel to the plane of the Equator. The
gnomon, which casts the shadow, passes through the centre of the dial and points
towards the South Celestial Pole. Since the Earth rotates once on its axis every 24
hours, covering 360 degrees, the Earth rotates 15 degrees every hour. The hour
lines are therefore equally spaced at 15 degree intervals. The gnomon is tilted
according to latitude (38 degrees for Melbourne).
Our Earth, Sun and seasons
As the Earth spins, the Sun appears to move across the sky. During summer, in the
Southern Hemisphere, the Sun rises in the south-east and sets in the south-west
but during winter, the Sun rises in the north-east and sets in the north-west.
In summer, the Sun has to move further to travel across the sky and reaches a
higher altitude in the sky than in winter. As a result, the summer shadow of the
gnomon lies on the uppermost face of the sundial, while the winter shadow lies on
the face underneath the dial plate.
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The following diagram illustrates the path of the Sun on:
(a)
The longest day of the year: Summer Solstice which usually occurs on
December 22.
(b)
The two days when the day and night are equal in length: Spring Equinox
usually on September 23 and Autumn Equinox usually on March 22.
(c)
The shortest day of the year: Winter Solstice usually occurs on June 22.
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On the Autumn Equinox and the Spring Equinox, the Sun rises due east and sets
due west. On these days there is no shadow cast on either side of the dial plate.
The shadow falls on the edge of the dial plate. Thus the sundial cannot be used to
tell the time on these two days of the year.
Making clock time equal solar time
Our Earth, Sun and seasons
Clock time is based on the average Sun time . In order for our sundial to read clock
time, we need to take some important factors into account.
Time correction
The sundial needs to be corrected for two main reasons. We need to compensate
for:
1.
The path of the Earth around the Sun being elliptical and the fact that the
Sun is slightly off centre of this elliptical path.
2.
The tilt of the Earth’s axis (23.5 degrees to the plane of the ecliptic).
We can use the universal Equation of Time graph to make the necessary correction.
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The Universal Equation of Time
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For simplicity, the following correction averages for each month can be used for
younger students.
Our Earth, Sun and seasons
Summer
Autumn
Winter
Spring
Dec ( - 5 min)
Mar (+ 8 min)
Jun (+ 1 min)
Sep ( - 5 min)
Jan (+ 7 min)
Apr (correct)
Jul ( + 6 min)
Oct ( - 14 min)
Feb (+ 14 min)
May ( - 3 min)
Aug (+ 4 min)
Nov (-14 min)
Longitudinal correction
Longitudinal correction should also be taken into account when adjusting the
sundial to read clock time. The Sun rises at different times at different places (or
longitudes) around the world. A standard system was developed so time could be
referred to universally. The 360 degrees of longitude of the Earth’s circumference is
divided into 24 zones, each covering 15 degrees of longitude. (In practice the zones
are altered in a few places to better fit the boundaries of the countries and islands.)
These zones are called Standard Time Zones.
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All places within these zones have the same defined clock time based on a set
longitude within these zones. The zero reference is taken to be at the Royal
Greenwhich Observatory in the outskirts of London.
Australia is divided into three Standard Time Zones: Western Standard Time
(Western Australia), Central Standard Time (South Australia and Northern Territory)
and Eastern Standard Time (Queensland, New South Wales, Victoria and
Tasmania). Sydney and Melbourne have the same clock time but Perth and
Melbourne have a two-hour difference. Adelaide and Melbourne have only half an
hour difference in clock time.
Adult Education at Scienceworks
Australian Eastern Standard Time (AEST) is referenced at 150 degrees longitude.
Melbourne is located at 145 degrees longitude. This five degree shift translates to
an error of 20 minutes between clock time and solar time for Melbourne. In order for
the sundial to read clock time, 20 minutes needs to be added to our sundial time in
Melbou r ne. ( If the s undial is to be u s ed out s i de of Melbourne s ubt r a c t an additional f our
minutes for every one degree longitude east of Melbourne or add an additional four
minutes for every one degree west of Melbourne.)
Lastly, during summer we move our clocks forward one hour to maximise the length
of evening. This means that the sundial will be an hour slow so an hour is added
onto the s undial ti m e du r ing da ylight s aving s . In Vi c t o r ia da ylight s aving u s ually
begins the last weekend in October and ends the last weekend in March.
Finding north using sunrise and sunset times:
The sundial is designed so that the gnomon points to the South Celestial Pole along
Our Earth, Sun and seasons
the north/south line. The Sun will be on the north/south line when the Sun is midway
between sunrise and sunset. If you measured the time the Sun was at its highest
point (or midway between sunrise and sunset), then you will be able to use the Sun
to find due north. Sunrise and sunset times for the year can be printed from the
Melbourne Planetarium web site. The following example shows how to calculate the
time that the Sun is midway between sunrise and sunset.
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Example:
In the month of May, 2000:
Monday
1
st
SUNRISE
SUNSET
7:01am
5:33pm
Monday:
1.
Convert the Sunset time to a 24 hour clock by adding 12 hours to the sunset
time.
12 hours + 5 hours and 33 minutes = 17hours and 33 minutes
Adult Education at Scienceworks
2.
Add this to the Sunrise time.
17 hours and 33 minutes + 7 hours and 1 minute
= 24 hours and 34 minutes
3.
Divide this value by 2.
24 hours and 34 minutes / 2
=12 hours and 17 minutes
This means that on Monday May 1, the Sun will be on the north/south line at
12:17pm. This is the time you should position your sundial so that the north face of
the dial points north. See the diagram below.
Please stress the dangers of looking directly at the Sun.
Follow the instructions on the template on the next page to make your sundial.
Our Earth, Sun and seasons
What you need
•
A4 template of sundial
•
A4 piece of cardboard
•
glue
•
scissors
•
piece of stiff cardboard (half an A4 sheet)
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What you do
Students are to:
1.
Paste the sundial template onto the cardboard.
2.
Cut around the dial following the heavy black line (illustration 1).
3.
Fold out the tabs along the dotted lines (illustration 2).
4.
Fold the dial plates (north and south circles) back to back and stick them
together with glue (illustration 3).
5.
Cut the V slot in the centre of the dial with the scissors (illustration 4).
6.
Cut out and fold the gnomon (illustration 5).
7.
Push the narrow end of the gnomon through the north face of the dial
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(illustration 6).
8.
Stick the tabs at the bottom of the dial to a piece of cardboard to act as a
stand.
9.
Cut out the table which gives the corrections for each month and stick this
somewhere on the stand to be used for reference.
10.
Follow the instructions on how to position the sundial so that the north face
points towards due north. The gnomon should stand at 90 degrees to the
dial face pointing towards the South Celestial Pole (illustration 7).
For more activities and information visit:
http://www.sundials.co.uk/intro.htm
Our Earth, Sun and seasons
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Adult Education at Scienceworks
Our Earth, Sun and seasons
32
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Activity 12: Different seasons
What you need
•
Research facilities
What to do
Go to the following websites and draw diagrams showing how the seasons in the
western culture differ from Australian Indigenous seasons.
http://www.deh.gov.au/parks/kakadu/artculture/seasons.html#gunumeleng
http://museumvictoria.com.au/forest/climate/kulin.html
Adult Education at Scienceworks
Questions
1 How does science explain the seasons in the modern western culture? Do you
have a preference? Why?
2 With refrigeration and transport, we no longer have seasonal food. What
difference has this made to our diet and lifestyle?
Our Earth, Sun and seasons
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