TOPIC 5: EARTH
1. THE ROTATING EARTH
1.1
Day and night
As the Earth rotates on its axis from west to east, the Sun appears to rise in the east and set in the
west.
From Dangerfield, Elizabeth, Thelma Pike, Helen Feutrill, Paul Holper, David Lloyd (1995)
Australian Secondary Science 1 Oakleigh, Vic. Cambridge University Press, p 197-198.
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1.2
Star trails
Locations on the Earth’s surface alternate between sunlight and
darkness -that is, day and night. During the night, stars appear to
shift in position slowly across the sky. If a camera is left outside
with its shutter open for several hours on a clear night, it will
record “star trails”, due to the apparent motion of stars across the
night sky.
We can explain this apparent motion if we recognize that it is
caused by the earth’s daily rotation on its axis.
Almost all stars appear to follow circular paths, but many of
the circles dip below the horizon at some time during the
night. These stars appear to rise and set. Some stars never
set. Their trails form complete circles around a point in the
sky: around the “south celestial pole” (for southern
hemisphere viewers) or around the “north celestial pole” (for
northern hemisphere viewers). Observers in the northern
hemisphere see Polaris, the North Star, as stationary - it
happens to be located almost at the North Celestial Pole.
There is no bright star at the South Celestial Pole.
1.3
Constellations
The night sky was well studied in earlier times: it acted as clock, calendar & compass.
It’s human nature to identify with patterns in nature: we “see” animal shapes in cave formations,
castles in clouds, and mythological creatures in star patterns. Cultures around the world identified
patterns in the night sky. Some Australian aboriginal communities identified the Large & Small
Magellanic Clouds (small galaxies near the Milky Way) as an old couple, keeping watch over the
members of their tribe; and the Milky Way as a river carrying the dead to their final resting place.
Labelling patterns in the night sky had practical importance too: it helped our ancestors learn to
orient themselves in space & time. They navigated by the stars, and used them to time their
seasonal activities. For example, Egyptians received yearly warning of the onset of the Nile flood
season when Sirius started to appear in the night sky. Astrology, the belief that stars could predict
future events probably arose from the use of observations of the stars to predict good times for
growing and harvesting crops.
Modern astronomers still use star groupings, called constellations, to identify regions of the sky. A
constellation is a grouping of stars which appear close together on the sky. In fact, they may not
be close together at all: some may be relatively close to Earth, while others in the same
constellation may be far away (but still bright enough to be seen). Constellation lines are the
patterns people have used over centuries, to find their way around the sky. Our modern system of
88 constellations is based partly on constellations first labelled in Mesopotamia, Babylon, Egypt
and Greece.
1.4
The Constellations of the Zodiac
The Sun appears to move across the sky during the day: it follows a path across the sky called the
ecliptic. This apparent motion is a consequence of the Earth’s rotation on it’s axis.
Over a year, the Earth orbits our Sun in an almost circular path: the imaginary surface on which the
circles of the Earth’s orbit lies is called the plane of the ecliptic.
Because the sun is so bright, we are unable to see any stars while the sun is in the sky. But, if we
could turn the sun off during the day, we would see stars, although not all of these stars are ones
we see at night. As the Earth moves around its orbit during the year, different stars are in the sky
at the same time as the sun. At any given time of the year, there will be some stars that lie directly
in line behind the sun, and we will not be able to see these stars at all. The constellations of the
zodiac are the constellations through which the Sun appears to pass each year.
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For example: The Sun is “in” Aquarius from February 18 - March 13. During this time, Aquarius
can’t be seen because it is “up” at the same time as the Sun - that is, during the day. Although we
do not see Aquarius in this period, in the month before the Sun is “in” Aquarius, Aquarius sets just
after the Sun does; and in the month after the Sun is “in” Aquarius, Aquarius sets just before the
Sun does. So to peoples who depended on watching the sky carefully, a constellation would be
very noticeable as it moves from being visible just after sunset, to be visible approximately one
month later, just before sunrise.
There are 13 constellations in the zodiac: Capricornus, Aquarius, Pisces, Aries, Taurus, Gemini,
Cancer, Leo, Virgo, Libra, Scorpius, Ophiuchus & Sagittarius. Ophiuchus does not feature in
astrology, but astronomers identify it as a zodiacal constellation, to fill a dark region of the sky that
was not named by astrologers.
The dates corresponding to the times when the sun is in each of the zodiacal constellations are not
the same as the dates commonly quoted for “star signs”. This is because the dates for the
astrological star signs were those that applied in ancient times. There have been changes in
Earth’s orbit over two thousand years, so the old dates are no longer accurate.
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2. THE CHANGING MOON
2.1 Phases of the moon
Like the planets, the Moon also follows a path close to the ecliptic across the night sky. But while
the planets orbit the Sun, the moon’s orbit is around the Earth. The Moon orbits the Earth with a
period of 27.3 days - a bit less than a month. As the moon orbits the Earth, to us on Earth, it
appears to change shape: from full moon to half moon to crescent moon … and back to full moon.
Astronomers refer to lunar phases:
 first quarter
 full moon
 third quarter
 New moon (or “no moon”)
The phases of the Moon arise because the orientation of the illuminated side of the moon changes
relative to the Earth, as the moon orbits the Earth. (The apparent change in shape is not due to the
shadow of the Earth falling partly on the Moon.)
Note that the far side of the Moon is not necessarily the dark side of the Moon, although it may be.
On the Internet, you can use John Walker’s “Earth and Moon viewer” site to see how the Moon
would look now from the Earth.
http://www.fourmilab.ch/earthview/vplanet.html2.2 Lunar eclipses
A lunar eclipse occurs when the Moon moves into the Earth’s shadow.
While in the Earth’s shadow, the Moon does not completely disappear: it appears dark and reddish.
This is because the red light in the sun’s spectrum is bent as it passes through the Earth’s
atmosphere. This red light illuminates the moon, so that we are still able to see it. (A similar effect
causes the setting sun to appear red.)
If you were on the near side of the Moon, looking at the Earth, while a lunar eclipse was taking
place, the Earth would appear dark and surrounded by a ring of reddish-tinged atmosphere.
2.3 Solar eclipses
Although the Sun is much larger than the Moon, it is also much further away. By a fluke of
creation, the apparent size of the Sun and the Moon are almost the same. Because of this
coincidence, we are occasionally treated to one of nature’s most spectacular events - a total solar
eclipse. During a solar eclipse the moon moves directly between the Earth and the sun.
Total solar eclipses give us a chance to observe the faint but beautiful outer layers of the Sun - the
chromosphere and the corona – which are normally “drowned out” by the bright solar photosphere.
The Moon’s shadow traces a path over the Earth: observers see a total eclipse where the central
dark part of the shadow passes. Observers in the grey “rim” of the shadow will see the Sun partly
but not completely obscured - a partial solar eclipse.
Solar eclipses might be expected to happen somewhere on Earth every month,but the 5o tilt of the
Moon’s orbital plane limits the chances of the Sun, Moon and Earth being
in alignment.
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From Dangerfield, Elizabeth, Thelma Pike, Helen Feutrill, Paul Holper, David Lloyd (1995)
Australian Secondary Science 1 Oakleigh, Vic. Cambridge University Press, p 203.
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From Dangerfield, Elizabeth, Thelma Pike, Helen Feutrill, Paul Holper, David Lloyd (1995)
Australian Secondary Science 1 Oakleigh, Vic. Cambridge University Press, p 199.
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3. EARTH’S SEASONS
3.1 Variations in the Earth’s distance from the sun
The Earth’s orbit around the sun is an ellipse,
but very nearly circular.
At its closest the Earth is
147.5 million km from the
sun.
This occurs in early
January.
At its furthest the
Earth is 152.6 million
km from the sun.
This occurs in early
July.
The difference is about 5 million km
or 2% of the Earth-sun distance!
Picture from
http://science.nasa.gov/headlines/y2001/ast03jul_1.htm
The Earth’s rotational axis is tilted by 23½o with respect to a line drawn perpendicular to the plane
of the ecliptic. The tilt of the Earth’s axis changes the distance between the Earth and the sun by
about 2,000 km, or 0.0025%. This is very small compared to the variation in the distance between
the Earth and the Sun.
3.2 The seasons
As the Earth orbits the Sun, the
seasons change
Northern spring
Southern autumn
Northern winter
Northern summer
Southern winter
Southern summer
Northern autumn
Southern spring
In the northern hemisphere summer the tilt of the Earth’s rotational axis means that the Sun is
higher in the sky in daytime in the northern hemisphere, than in the southern hemisphere, which
will be in winter.
In Summer when the Sun is higher in the sky, each beam of sunlight is spread out less when it
hits the ground than in winter, when the Sun is lower in the sky. So for the hemisphere
experiencing Summer, sunlight striking the Earth is more concentrated and this helps to raise the
average temperature. The reverse is true for the hemisphere experiencing Winter.
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When the northern hemisphere is in midsummer the north pole has continuous daylight, and
locations in the northern hemisphere have long days. Locations in the southern hemisphere have
long nights, and the south pole is in continuous darkness. Long periods of daylight help to warm
the hemisphere experiencing Summer, more than the hemisphere experiencing the short periods of
daylight and long cold nights of winter.
So, there are 2 major reasons for the seasons on Earth:
 the amount by which sunlight striking the earth is spread out, depending on whether the
sun is high (summer) or low (winter) in the sky.
 the differing length of daylight hours in each hemisphere.
Both these effects are due to the tilt of the Earth’s rotational axis:
Precession of the Earth’s orbit
The direction of the rotational axis of the Earth is not fixed in space. Forces due to the Sun & Moon
cause it to very slowly rotate: This is called precession. Over a period of 26,000 years, the
earth’s rotational axis “precesses” through a complete cycle.
This precession has gradually shifted the positions of the constellations in the sky, and, in
particular, the periods of the year which correspond to each zodiacal constellation. Precession
also changes the locations at which seasons occur in the Earth’s orbit. The Earth is now closest to
the Sun during southern Summers, but in about 13 000 years this will occur during northern
Summers.Southern Summers may become more mild, and northern Winters may become more
severe.
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From Dangerfield, Elizabeth, Thelma Pike, Helen Feutrill, Paul Holper, David Lloyd (1995)
Australian Secondary Science 1 Oakleigh, Vic. Cambridge University Press, p 200-201.
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4. A BRIEF HISTORY OF EARTH
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5. GLOBAL WARMING
5.1 The Earth’s energy budget
Short wave radiation from the sun, long wave from the earth
The earth receives a total of 1.8 x 1017 J of energy from the sun each second. The diagram shows
how the radiant energy emitted by the sun is distributed across the wavelengths of the
electromagnetic spectrum. This distribution across the wavelength range depends only on the
temperature of the surface from which the energy came.
The energy absorbed by the earth and the atmosphere makes them warm, so they in their turn
radiate energy. The average temperature of the ground over the earth is a bit less than 300 K, and
the average for most of the atmosphere is just a bit lower. The range of wavelengths emitted by
objects at this temperature is shown in the diagram.
Diagrams from : Bob Crowder
The Wonders of the Weather
Melbourne, Bureau of
Meteorology 2000: p 22-23.
The range of wavelengths emitted by the earth is almost completely separate from the range of
wavelengths received from the sun. Nearly all the radiation from the sun has a wavelength less
than 0.2 x 10-6 m. This is often called short-wave, or solar, radiation. Nearly all the radiation
emitted by the earth is infra-red radiation with a wavelength longer than 0.2 x 10-6 m. This is often
called long wave, or terrestrial, radiation.
Energy from the sun
At the top of the atmosphere, if the sun is directly overhead, 1365 J of energy are received by one
square metre in each second. As you move towards the poles this amount of energy becomes
spread over a larger area of the earth's surface. So, at the equinox, when the sun is over the
equator, each square metre at the top of the atmosphere in southern Australian latitudes (about 40
S) receives about 1000 J of energy in each second at the middle of the day.
The total amount of radiant energy that the earth receives from the sun must balance the amount it
radiates to space, because the temperature of the earth overall remains about constant. But at the
tropics, more radiant energy is received than is lost, and at the poles more radiant energy is lost
than is received. And yet, in spite of the imbalance, the temperature at the tropics does not
increase over a long time, and neither does the temperature at the poles decrease. This is
because the prevailing winds transfer energy, by (forced) convection, from the tropics to the poles.
Most of the radiant energy that arrives at the top of the atmosphere from the sun passes through
the atmosphere. In other words, the atmosphere is hardly heated at all by the energy coming from
the sun; the atmosphere is transparent to solar (short wave) radiation.
The exception is that the ozone in the atmosphere absorbs most of the energy in the ultra violet
region. The ozone is concentrated at heights above 20 km from the surface of the earth and as
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result the atmosphere at this height is considerably warmer than above or below. Small amounts
of energy are also absorbed by water vapour in the atmosphere, and by the water droplets in
clouds.
Energy from the Earth
What happens to the energy reaching the earth from the sun
Diagram from Christina Hart, Margaret Mazzonlini, Russell Tytler, Tony Callaghan (1991) Physics:
Revealing Our World Milton, Qld. Jacaranda Press: p 146.
Out of every 100 J of the sun's energy that reaches the top of the atmosphere, a total of about 20 J
are absorbed in the atmosphere. Of the remaining 80 J, some is reflected back to space without
warming the surface or the atmosphere. Clouds reflect about 22 J and about 3 J are reflected from
the surface itself. The molecules of the atmosphere and dust particles also scatter some energy,
but most of this still arrives at the surface after being scattered. Overall, about 50 J of energy are
eventually absorbed by the ground and warm it.
Energy absorbed by the atmosphere
Diagram from : Bob Crowder The Wonders of the Weather Melbourne, Bureau of Meteorology
2000: p 23.
A large amount of the radiation from the earth is absorbed by the atmosphere. The atmosphere is
heated as a result and radiates in its turn. Much of the radiant energy from the atmosphere heats
the ground, so that as a result the ground is able to emit more radiant energy than it receives
directly from the sun. The atmosphere acts like a trap for the long wave radiation, and continually
recycles some of it back to the ground, rather than allowing it to escape directly to space.
The atmosphere thus behaves rather differently towards the long wave radiation from the ground
than it does to the short wave radiation from the sun. Most of the energy from the sun passes
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straight through the atmosphere but, in contrast, the atmosphere readily absorbs most of the
radiation coming from the ground. Actually specific gases, which are present in the atmosphere
only in very small amounts, are responsible for this absorption of long wave radiation. The most
important of these are carbon dioxide (CO2) and water vapour (H2O), but methane (CH4), nitrous
oxide (N2O), and the chloro-fluoro-carbons also make significant contributions. The wavelengths of
radiation absorbed by these gases is indicated in the diagram. The wavelengths absorbed by
ozone (O3) are also shown for comparison.
How a greenhouse works
A greenhouse, or glasshouse, is valuable to
gardeners because it allows them to create a warm
environment for their plants to grow. A greenhouse
uses only the energy available from the sun, although
during winter this can be supplemented by other
means. Part of the natural warming effect comes
about because glass is transparent to the short-wave
radiation from the sun, but not to the long-wave
radiation. The radiant energy from the sun passes
through the glass and is absorbed by the plants and
pots and soil inside. These become warm and
radiate energy themselves, but in the long
wavelengths which cannot pass through the walls of
the green house. This radiation is reflected by the
walls and may be absorbed by the plants and air
inside, so the contents of the greenhouse become
warmer than they would have been if the long
wavelength radiation had escaped.
How a greenhouse traps energy
Diagram from Christina Hart, Margaret
Mazzonlini, Russell Tytler, Tony Callaghan
(1991) Physics: Revealing Our World Milton,
Qld. Jacaranda Press: p 153.
Of course, as the air inside heats up, the glass walls themselves become warm, so that they
radiate an increasing amount of energy. Eventually a point is reached where the amount of
radiation lost by radiation from the walls of the greenhouse equals the amount from the sun that is
coming in, and so the temperature does not increase any more.
The glass walls of the greenhouse therefore act like a radiation trap, producing a higher
temperature inside than out. This trapping of radiation is often called the 'greenhouse effect', and it
occurs also in cars and buildings that are exposed to the sun's radiation. In fact, however, a more
significant effect of a greenhouse is to stop the loss of heat by convection, both forced and free,
from the plants.
But although the 'greenhouse effect' may not be very important in keeping the greenhouse warm
the same effect is important in keeping the earth and its atmosphere warmer than they would
otherwise be. We have already noted precisely this effect in the large amount of energy that is
radiated back to the ground from the atmosphere. This action of the atmosphere, or rather of
specific gases in the atmosphere, is sometimes referred to as the 'atmospheric greenhouse effect'.
3.2 Climate change
The warming Earth
The temperature of the earth appears to stay constant overall, but in fact of course in the past there
have been significant variations in climate, resulting in the ice ages, and less dramatic changes in
climate can also be inferred from geological and biological data. The temperature changes
involved in such climate changes are quite small. Even during the last ice age the average
temperature over the earth was probably only about 5 C lower than at present, but this shows how
dramatic the effects of even a small temperature change can be.
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Over the past 100 years there has been a small but steady rise in temperature. Climatologists
believe this warming is due to increasing concentrations in the atmosphere of the greenhouse
gases. The most important of these
gases is carbon dioxide. Sources of
carbon di-oxide in the atmosphere are
respiration (breathing) of animals and
plants, the decomposition of plant and
animal matter, and the burning of fossil
fuels. Photosynthesis removes carbon
dioxide from the atmosphere.
Diagram from: National Greenhouse
Advisory Committee(1995) Warming to
the Issue – Australian Science Comes
to Grips with Greenhouse
Commonwealth of Australia: p 46.
Temperature anomalies over Eastern Australia
Increases in atmospheric concentrations of the greenhouse gases
Concentrations of carbon dioxide in the atmosphere have been rising steadily since the beginning
of the industrial revolution, as a result of the burning of increasing amounts of fossil fuels.
Calculations based on the amounts of fuels that have actually been burnt suggest that the
increases in concentrations should have been about twice what has been observed, but the oceans
appear to have absorbed the difference.
Concentrations of the other greenhouse
gases (the chloro-fluoro-carbons, methane
and nitrous oxide) have also increased over
the same period as a result of industrial and
agricultural processes. Although these gases
are present in much smaller amounts than
carbon dioxide they are much more effective
absorbers of infra-red radiation on a
molecule-for-molecule basis, so that together
they could produce a warming effect roughly
equal to the effect of carbon dioxide alone.
Diagram from: National Greenhouse Advisory
Committee(1995) Warming to the Issue –
Australian Science Comes to Grips with
Greenhouse Commonwealth of Australia:
p 23.
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Measurements of carbon di-oxide and methane
concentrations in the atmosphere
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It is very difficult to estimate future concentrations of the
greenhouse gases, and even more difficult to predict what
effect expected increases might have on the earth's climate.
Complex computer models of the earth and the atmosphere
have been developed to study the possibilities. Most models
predict that by the middle of this century the average
temperature of the earth will have increased by between 1.54.5 C. This sounds like a small increase - until you compare
it with the average temperature change during the last ice
age.
Diagram from: National
Greenhouse Advisory
Committee(1995) Warming to
the
– Australian
Science
The Issue
relative
energy absorbing
Comesoftothe
Grips
with
ability
greenhouse
gases
Greenhouse Commonwealth of
Australia: p 12.
A variety of feedback mechanisms within the earth's
atmosphere may operate to increase or decrease the
expected temperature rise. For example, the oceans with
their huge heat capacity will absorb extra energy. This will
delay the expected temperature rise. On the other hand,
snow and ice will melt. These presently reflect large amounts
of the sun's radiant energy, and without them more of the
energy from the sun will be absorbed. This would give a
positive feedback effect, increasing the size of the expected
temperature rise. The amount of cloud could also change.
Depending on the type of cloud, this could have either a
negative feedback effect by increasing the amount of the
sun's radiation that is reflected, or a positive feedback effect
by trapping more of the earth's infra-red radiation.
3.3 What should we do?
Nothing:
 the economic cost is too great
 the science is uncertain
 the effects might be positive
Take action:
 scientific uncertainty is now about the magnitude, not the reality of the effect
 possible sudden changes as Earth’s adaptation mechanisms change (e.g. capacity of
oceans to absorb CO2 is reached)
 the effects could be catastophic - taking no action is irresponsible
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TO THINK ABOUT
Your starting points
1. The cycle from the light of day to the dark of night is one of the most familiar aspects of
our lives. But why does this change occur?
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Draw a diagram to illustrate your answer.
How many other questions occur to you as you try to answer this question?
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2. Over the course of the year, Melbourne experiences the heat of summer and the cold of
winter, with autumn and spring in between. What causes these seasonal changes?
Draw a diagram to illustrate your answer.
How many other questions occur to you as you try to answer this question?
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3. At some times we see a full moon, and at other times a crescent moon, as well as various
shapes in between. What causes these changes in the moon’s appearance?
Draw a diagram to illustrate your answer.
How many other questions occur to you as you try to answer this question?
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Thinking about the moon
1.
The moon takes 27.3 days to orbit the earth, and the same side of the moon always faces
towards Earth. How long is a ‘day’ on the moon?
2. Can a solar eclipse occur at any phase of the moon? Why, or why not? Illustrate your
answer with clear diagrams.
3. Can a lunar eclipse occur at any phase of the moon? Why, or why not? Illustrate your
answer with clear diagrams.
4. The planet Venus also goes through phases, as seen from Earth. So does Mercury, but
these are much harder to see (why?). Why does Venus appear to go through phases?
Why is it only the planets Venus and Mercury that show phases?
(Note: This was one of the pieces of evidence for a sun-centred model of the solar
system, that Galileo found with his telescope, and with which he tried to convince others
of the reality of the sun-centred model.)
5. Scale is important in drawing diagrams to explain eclipses, both lunar and solar. Why? An
accurate scale is difficult to show on paper. (Why?). However, with a little effort and a
large sheet of paper, you can do a lot better than the average text book. Try it.
6. Everyone on Earth will see a lunar eclipse if it happens at a time when they are on the side
of the Earth facing the moon.
However, a solar eclipse will be seen by only a relative few of the people who are on the
side of the Earth facing the sun at the time of the eclipse.
Explain why this difference arises. Draw a diagram to illustrate your explanation.Thinking
about the seasons
1.
One of the difficulties books have in trying to explain why we have seasons on Earth, is
that the diagrams used to illustrate the explanations are not drawn to scale.
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In fact it is very difficult to draw a good scale diagram that is effective for this purpose.
Why? However, with a little effort and a large sheet of paper, you can do a lot better
than the average text book. Try it.
From J. M. Ash et al (1987) Elements of Science Book 1 Melbourne, Longman Cheshire; p 193.
2. The following pictures of Earth were taken by satellite. What time of day was it in
eastern Australia when each picture was taken? What season was it when each picture
was taken?
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Pictures from: Bob Crowder The Wonders of the Weather Melbourne, Bureau of Meteorology
2000: p .
3. The picture was taken during midsummer,
at Macquarie Island, one of Australia’s
Antarctic Research Stations. The
timelapse image shows the path of the sun
as it moves across the sky. Explain why
the sun does not set, but always remains
low in the sky.
Picture from: Bob Crowder The Wonders of
the Weather Melbourne, Bureau of
Meteorology 2000: p .
4. The angle of tilt of the moon’s axis is 5º: this is the angle between the moon’s axis of
rotation, and where the axis would be if it was perpendicular to the plane of the moon’s
orbit. Would there be seasons on the moon? Why or why not?
5. The tilt of a planet is the angle that its axis of rotation makes with a line drawn
perpendicular to the plane of the ecliptic. In the case of Earth, the angle is 23½º, and
the orientation of the axis stays constant as the Earth orbits the sun.
The axis of the planet Uranus has a tilt of 90º - in other words, its axis of rotation is in
the plane of the ecliptic, pointing towards the sun. The orientation of the axis stays
constant as Uranus orbits the sun.
Would there be any seasons on Uranus? What would day and night look lie on Uranus?
Illustrate your answer with clear diagrams.
6. Other planets have an angle of tilt that is greater than Earth’s, but less than that of
Uranus. How would the seasons on these planets differ from Earth’s seasons? Would day
and night be any different? Why or why not? Illustrate your answer with clear diagrams.
7. Some planets have a smaller angle of tilt than Earth’s. How would the seasons on these
planets differ from Earth’s seasons? Would day and night be any different? Why or why
not? Illustrate your answer with clear diagrams.
Think about global warming
1.
Conduction and convection play a part in the transfer of energy from the ground to the
atmosphere, but all the energy that is transferred from the earth to space is radiant
energy. Why do conduction and convection not contribute?
2. Both the sun and the earth emit radiant energy. In what ways is the radiant energy
emitted by the earth similar to that emitted by the sun, and in what ways is it different?
You also emit radiant energy. Which would be more similar to the type of radiant energy
you emit, the radiant energy from the sun or from the earth? Explain your answer.
3. If the earth radiates as much energy to space as it gains from the sun, how can the
temperature of the earth be so much lower than the temperature of the sun?
4. Carbon dioxide, nitrous oxide and methane are often referred to as the 'greenhouse
gases'. Why do you think they are given this name?
5. With or without absorbing gases in the atmosphere, the amount of radiation emitted by
the earth would be equal to the amount received from the sun. In other words the
presence of the greenhouse gases does not decrease the total amount of radiation that is
lost from the ground and atmosphere. Why then is the temperature near the ground
higher with these gases present than it would be without?
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6. How do you think the total amounts of incoming radiation from the sun, and/or outgoing
radiation from the earth would be affected by the following changes:
a) an increase in the amount of dust in the atmosphere
b) a decrease in the amount of ozone in the atmosphere
c) an increase in the amount of water vapour in the atmosphere
d) an increase in the amount of carbon dioxide in the atmosphere
e) an increase in the amount of cloud
Overall, in each case, would you expect that the temperature would increase or decrease?
Why?
7. The moon does not have an atmosphere. How do you think you would find the temperature
on the moon compared with the temperature on earth? Would the temperature vary more
or less over a day on the moon compared with on the earth? What would be the source of
energy to heat the moon? What process(es) would be important in transferring heat away
from the surface of the moon? How does this compare with what happens on earth?
8. Your body's temperature control mechanism is an example of a feedback process. Is it a
positive or negative feedback? Explain your answer.
Denying the green house
Read the article “Denying the greenhouse. How many misleading arguments can you identify?
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WORKSHOP 8 AND 9: THE SOLAR SYSTEM
A model of the solar system
Your task is to build a scale model of the solar system, using the data below.
Name
Orbits
Distance (000 km)
Sun
Radius (km)
Mass (kg)
697,000
1.99x1030
Jupiter
Sun
778,000
71,492
1.90x1027
Saturn
Sun
1,429,000
60,268
5.69x1026
Uranus
Sun
2,870,990
25,559
8.69x1025
Neptune
Sun
4,504,300
*24,764
1.02x1026
Earth
Sun
149,600
6,378
5.98x1024
Venus
Sun
108,200
6,052
4.87x1024
Mars
Sun
227,940
3,398
6.42x1023
Ganymede Jupiter
1,070
2,631
1.48x1023
Titan
Saturn
1,222
2,575
1.35x1023
Mercury
Sun
57,910
2,439
3.30x1023
Callisto
Jupiter
422
1,815
1.08x1023
Io
Jupiter
1,883
2,400
8.93x1022
Moon
Earth
384
1,738
7.35x1022
Europa
Jupiter
671
1,569
4.80x1022
Triton
Neptune
355
1,353
2.14x1022
Pluto
Sun
5,913,520
1,160
1.32x1022
Use your model to explain:
1.
why the sun appears to move across the sky during the day;
2. why constellations appear to move across the sky at night;
3. why the shape of the moon appears to change over a period of about 28 days;
4. how solar and lunar eclipses occur;
5. how the angle of the sun’s rays changes over a day, causing temperature variations
over a 24 hour period;
6. how the angle of the sun’s rays at noon varies from the poles to the equator, causing
temperature to vary with latitude;
7. why the length of daylight in Melbourne is longer in summer than in winter;
8. how the changing angle of the sun’s rays changes over a year, causing seasonal
variations in temperature;
9. why we see different constellations in the night sky in summer and winter.
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CONSOLIDATING AND GOING FURTHER
References
Skamp Chapter 2, , Chapter 10 and Chapter 12.
About teaching and learning science and technology
Adams, Raymond, Brian Doig and Malcolm Rosier (1991) Science Learning in Victorian Schools:
1990 Melbourne, Australian Council for Educational Research.
Bourke, Jane (1997) Using the Internet to Research Astronomy and Space Ready-Ed Publications,
Greenwood W.A.
This book contains astronomy activities that make use of Internet resources. The activities
are in photocopiable form, and are suitable for use with children in grades 5 and 6.
Available from: Read-Ed Publications, PO Box 276, Greenwood, W.A.
The publisher’s web site is:
http://www/iinet.net.au/~edubooks
Crowther, David T. (1997) “The constructivist zone” The Electronic Journal of Science Education 2
(2) http://unr.edu/homepage/jcannon/ejse/ejsev2n2ed.html
Gallas, Karen (1995) Talking their Way into Science: Hearing Children's Questions and Theories,
Responding with Curricula New York, Teachers College Press.
Fleer, Marilyn, Tim Hardy, K. Baron, K, Cliff Malcolm (1995) They Don't Tell the Truth About the
Wind. Carlton Vic, Curriculum Corporation.
Koch, Janice (1999) Science Stories: Teachers and Children as Science Learners Boston/New
York, Houghton Mifflin. See Chapter 10: Making models- explorations of the solar system.
Nussbaum, Joseph (1985) “The Earth as a Cosmic Body” in Rosalind Driver, Edith Guesne and
Andree Tiberghien (Eds) Children’s Ideas in Science London, Open University Press; p 170-192.
Osborne, Roger and Peter Freyberg (1985) Learning in Science: the Implications of Children’s
Science Auckland, Heinemann.
Tromp, Calvin (1999) “Scaling the Solar System” Let’s Find Out Issue 5 p 23-25.
This article is from the magazine Let’s Find Out, published by the Science Teachers
Association of Victoria for teachers of primary science. It includes some useful practical
tips on building a model of the solar system with primary school-age children, as well as
some further Internet sites with useful information.
Rodrigues, S and Corrigan, D. (1998) Including IT: Managing information technology in the science
classroom User Friendly Resources.
Rodrigues, S (1998) The wired classroom User Friendly Resources.
Provides a few examples involving the use of ICT in teaching and learning science in primary
schools.
(User Friendly Resources P.O. Box 278 Annandale NSW 2038, Phone 1800 553 890, Fax
1800 553 891)
Southwest Education Development Laboratory (1995) “Building an understanding of
constructivism” Classroom Compass (online journal) available at
http://www.sedl.org/scimath/compass/v01n03/welcome.html
Victorian Curriculum and Assessment Authority (2005) Sample Unit: Out of This World VCAA East
Melbourne (available at http://vels.vcaa.vic.edu.au/support/level4/index.html)
West, Heather (2000) “Prior knowledge? Constructivist approach?” Let’s Find Out 17 (1) p 51-53.
About the science
Crowder, Bob (2000) The Wonders of the Weather Melbourne, Bureau of Meteorology.
Farrow, Steve (1999) The Really Useful Science Book: A Framework of Knowledge for Primary
Teachers (2nd Edition) London, The Falmer Press.
Grice, Noreen (2002) Touch the universe: A NASA Braille Book of Astronomy Washington, DC :
Joseph Henry Press.
Using tactile illustrations combined with Braille captions Noreen Grice ... presents the sky
in a way I'd never envisaged. Sighted people should close their eyes to touch the Eagle
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Nebula. It will never seem the same again. This book doesn't merely fill in the gaps for
people with impaired vision, it adds a whole new dimension for those of us who have
already seen the phenomena depicted here. ... Can I implore sighted people to tell their
Braille reading friends about this book? (New Scientist 22/3/2003)
Hart, Christina, Margaret Mazzonlini, Russell Tytler, Tony Callaghan (1991) Physics: Revealing Our
World Milton, Qld. Jacaranda Press.
Levy, David Starry Night: Astronomers and Poets Read the Sky Prometheus. (Reviewed New
Scientist 10 march 2001, p 53.)
Kaufmann, William, Roger Freedman (2000) Universe New York, W. H. Freeman and Company.
(UniM ERC 523KAUF)
Plait, Philip (2002) Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the
Moon Landing Hoax New York, Wiley.
Pratchett, Terry, Ian Stewart, Jack Cohen (2002)The Science of Discworld London, Ebury Press
(Chapter 4: Science and magic; Chapter 8: A giant leap for moonkind).
Sellars, David (2001) The Transit of Venus: The Quest to Find the True Distance of the Sun Leeds,
Magavelda Press.
Web sites
The site marked * are linked directly from lecture slides.
Melbourne Planetarium
*http://www.museum.vic.gov.au/planetarium/
The Melbourne Planetarium science works museum presents a spectacular site focusing on
aspects of space. The site imparts information on the planets, space exploration, the moon, the
sun, stars and the universe and ‘What’s in the sky’. Learn facts and information about each of the
planets by clicking on visual diagrams. Under the heading ‘stars and the universe’ learn about the
four seasons and the meaning and background to constellations. It also provides the latest
information on space and occurrences within the universe for general interest.
Earth and the seasons
*http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Seasons.shtml
Earth and the seasons is a brilliant, user friendly site that encompasses a wide range of information
and pictorial graphics that will enhance learning. The site focuses on how seasons change, why
they change and the tilt of the Earth's axis. Through pictorial diagrams and graphs, visitors can
learn all about each planet and how it compares with Earth. At the conclusion of each page, there
are exciting science activities. From each page there are several extended links that contain
additional information. The site is a delightful learning tool for students to use because the
information is clear and supported by visual images.
*http://www.worldbook.com/fun/seasons/html/seasons.htm
The World Book site provides information about the four seasons that comprise our yearly
calendar; the causes of the seasons, a description of seasonal changes, what an equinox is, etc.
You can test your knowledge and understanding of the seasons through the ‘Seasons quiz’.
Excellent for grasping a basic understanding of the seasons, this site is enhanced through a
diagram showing how the tilt of the earth’s axis effects the seasons, the seasonal quiz and an
activity on autumn leaf identification.
Another useful explanation of the seasons can be found at:
*http://www.morehead.unc.edu/Shows/EMS/seasons.htm
Earth and Moon
*http://www.fourmilab.ch/earthview/vplanet.html
Earth and Moon Viewer is a visually stunning site that allows you to view the earth in various ways:
through day and night regions and views from the sun. You can examine the earth from any
location by entering specific latitude, longitude and altitude readings from a satellite in earth’s orbit
or various cities around the world. A multitude of different images can be generated to give a
different view of earth in spectacular fashion. In addition images of the moon can also be viewed in
similar ways to the earth. Useful for students learning about planets to grasp a view of the world
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and planet positions from a unique perspective. The images generated by this site are amazing
and allow for an awe-inspiring view of the earth and moon at various phases of its existence.
The American Navy site (http://aa.usno.navy.mil/data/) provides information on the phases of the
moon, equinoxes and eclipses and much else. There is a virtual reality calculator
(http://tycho.usno.navy.mil/vphase.html) that shows the phase of the moon at any time and date
from 1800-2199 A.D.
The following site gives a panoramic view of the earth at night taken from the space station. You
can scroll from east to west and north to south:
http://antwrp.gsfc.nasa.gov/apod/image/0011/earthlights_dmsp_big.jpg
Eclipses
The following sites contain helpful explanations and information about the moon’s orbit, eclipses,
and how often eclipses occur.
*http://astrosun.tn.cornell.edu/courses/astro201/eclipse.htm
*http://www.scienceu.com/observatory/articles/eclipses/eclipses.html
*http://www.ebtx.com/theory/eclipse.htm
*http://www.earthview.com/tutorial/tutorial.htm
*http://www.coolquiz.com/trivia/didyouknow/eclipse.asp
The night sky
*www.heavens-above.com
This site enables you to view a map of the night sky for any date, time and almost any place you
wish. The constellations are marked, and planets shown. For beginning observers of the night sky
this is a wonderful resource.
http://home.mira.net/~reynella/skywatch/ssky.htm
Detailed monthly notes on the Southern sky, including charts showing the planets and bright stars
and guidance for finding your way around the night sky. There is also information about other
events in the sky: the moon’s phases, auroral displays, meteor showers, Iridium Flares, the
International Space Station and appearances of other artificial satellites
Planets and the solar system
http://planetscapes.com/solar/eng/earth.htm
‘Views of the Solar system’ presents a stunning image of multimedia describing the planets, moon,
asteroids and comets and the data of each. Visitors can learn about the history of space
exploration and rocketry, early astronauts, missions to space and the space shuttles, through an
extensive collection of photographs, facts, graphics and video images.
Further information about the planets and solar system can be found at http://wwwhpcc.astro.washington.edu/scied/astro/astroimage.html. A collection of some of the best images
from the NASA planetary exploration program is included.
There is a mirror for this site at: www.curtin.edu.au/mirror/planets
http://www.seds.org/billa/tnp
On this site you can take a tour of the solar system with pictures, text, movies and references to
other Internet resources. There is an overview of the history, mythology, and current scientific
knowledge of each of the planets and moons in our solar system
There is a mirror for this site at: http://www.anu.edu.au/Physics/nineplanets/nineplanets.html
*http://www.bbc.co.uk/science/space/solarsystem/index.shtml
This BBC site offers a multimedia travel guide to the solar system.
http://www.athena.ivv.nasa.gov/curric/space/index.html
The Space and Astronomy web site focuses on each planet, models of the planetary system with
visual images accompanied by information and provoking questions for students. Solar system task
cards (worksheets) allowing students to fill in the gaps to questions about the solar system which
help to cement learning. A vivid multimedia exploration of the solar system gives clear images of
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the planets that comprise the universe and accompanied with spectacular video footage, this is a
site worth viewing.
http://www.kapili.com/risec/index.html
This easy-to-use site features information on stars, the universe, galaxies and the solar system.
There are links within each topic to other related topics on the site. Under the topic of the solar
system there are illustrations of each of the planets and information about them, as well as a brief
outline of the evolution of the solar system.
The Exploratorium site (http://www.exploratorium.edu/ronh/solar_system/index.html) includes a
program that will help anyone who has trouble with scales in building a model of the solar system.
You can enter the size of your sun, and the program automatically calculates the sizes of the
different planets and their distance from the sun on the same scale.
Space exploration
http://www.spaceflight.nasa.gov
This is the NASA home page. There are links to information about space exploration, space
stations, the Hubble space telescope, satellites, comets and other topics in astronomy.
Amongst the wealth of information on the NASA site is
http://science.nasa.gov/headlines/y2001/ast03jul_1.htm The earth’s orbit is elliptical, not circular,
which means that at certain times of the year we are closer to the sun than at others. But this is
not the cause of the seasons, and in fact the average temperature of the earth is lowest when the
earth is furthest from the sun. This link explains why.
http://sin/fi/edu/tfi/hotlists/space.html
Includes hotlists for the solar system, space travel/exploration, distant stars, background
information, images and teacher resources.
Astronomy in different cultures
Nearly all religions set the dates of some festivals according to astronomical events. The date of
Easter in the Christian calendar is set according to complex rules involving the equinox and phase
of the moon, that are explained on this site: *http://www.assa.org.au/edm.html#Method. The date
for Chinese new year also depends on the phase of the moon, and the date of the (northern
hemisphere) winter solstice; see *http://www.math.nus.edu.sg/aslaksen/ for information on this, as
well as calendars in Islamic and Indian cultures.
The following sites provide information about the constellations as named by different cultures, and
the mythology attached to them.
Geek and Roman:
*http://domeofthesky.com/clicks/constlist.html
*http://einstein.stcloudstate.edu/Dome/constellns/constlist.html
Chinese:
*http://users.erols.com/bcccsbs/chisacw.htm
South African:
*http://www.rog.nmm.ac.uk/leaflets/constellations/constellations.html
*http://www.saao.ac.za/starlore/legends.html
Australian Aboriginal:
*http://www.questacon.edu.au/html/aboriginal_astronomy.html
History of astronomy
Ancient civilisations depended on astronomical observations. The following sites explain why, and
describe some of what we know of achievements of ancient astronomers. Until recent times,
eclipses were believed to be portents of doom. The Babylonians may have been able to predict
eclipses, but this a matter of controversy, as you can find out.
*http://www.livius.org/k/kidinnu/kidinnu.htm
*http://www.stormpages.com/swadhwa/hofa/mesopotamia.html
http://museumeclipse.org/about/history.html
(also at: http://eclipse99.nasa.gov/pages/traditions_Calendars.html)
Astronomical misconceptions
In lectures we have discussed misconceptions about the earth commonly held by children, and we
probably identified some misconceptions that you held. If you would like to be reassured that you
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are in good company, you might like to know that the overwhelming majority of new Graduates
from Harvard University, one of the most prestigious universities in the United States, were unable
to correctly say why the earth has seasons! You will find a long catalogue of common
misconceptions in astronomy at the following website: www.umephy.maine.edu/ncomins
Another sites featuring common misconceptions is at: http://www.badastronomy.com/
Astrology
Do you think that ‘astronomy’ and ‘astrology’ are much the same? As far as most scientists are
concerned astrology is not science, but astronomy is. The differences between the two are
discussed on the following site:
*http://www.skeptics.com.au/journal/astrol.htm
Resources for schools and teachers
http://www.spacekids.com/
A colourful and animated site, ‘Spacekids’ provides a multitude of information supported by video
images, diagrams and information aimed at children, yet very informative for anyone searching for
a vivid informative boost into space. Equipped with information for both students and teachers, the
resources on this site provide a unique and interesting insight into space and the solar system.
Under the category ‘Solar system’ this offers information and clear colored illustrations on each
planet, diagrams showing their relative size and distance from the sun and a brief history of the
solar system. An excellent site equipped with a variety ensuring it is a great learning tool for all.
Here are some Internet sites that contain classroom activities suitable for use in primary schools.
http://amazing-space.stsci.edu/
http://www.earthsky.com/
Specifically Australian information can be found at:
http://astro.ph.unimelb.edu.au/central/home.html
Any questions?
The following site allows you to ask an astronomer a question. There are also answers to
questions other people have asked, making this an information rich site.
http://curious.astro.cornell.edu/index.php
Weather and the atmosphere
http://www.ucar.edu/educ_outreach/webweather/basic.html
Basic ingredients of the weather, clouds and thunderstorms
http://www.bom.gov.au
The Australian Bureau of Meteorology’s web site contains information about the weather and
climate, as well as the atmospheric greenhouse effect. There are a number of resources for
teachers.
Climate change
http://www.ipcc.ch/
The Intergovernmental Panel on Climate Change has produced a comprehensive set of reports
summarising both the science and social and economic consequences of global warming.
The synthesis report for 2001 is at: http://www.ipcc.ch/pub/un/syreng/spm.pdf
http://www.epa.gov/globalwarming/
The site of the United States Environment Protection agency provides comprehensive information
about global warming. You can discover what the greenhouse effect is, what causes it, the
difference between ozone depletion and global warming, the chemicals contributing to the
greenhouse effect and some of the things humans can do to solve or reduce the problem. This site
is user friendly although the information is in the form of text and diagrams. There is a Kids site
with resources for teachers.
http://www.pbs.org/wgbh/nova/warnings/
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This site supports a TV program broadcast by the PBS in the United States. It investigates the
consequences of the polar ice caps melting, and looks at the evidence that scientists use to build a
picture of the earth’s climate in the past. A ‘clickable’ ice core timeline reveals the information
about the past 300,000 years stored in the layers of ice.
http://www.guardianlimited.co.uk/globalwarming
Work out how much carbon dioxide you contributed to the atmosphere today.
Using data-loggers in the primary school
http://www.concord.org/newsletter/2002-fall/probeware.html
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