Takapuna Grammar Level 1 Science

Transcription

1 Takapuna Grammar Level 1 Science Notes and exercises for NCEA S1.15: Astronomical cycles and their effects on planet Earth 2 single-lesson tests for a combined 4-credit internal AS Table of Contents: Overview of the content in this NCEA achievement standard:... 2 Introduction Fact or myth? The reason for the seasons: What causes the seasons? The Earth s tilt The day the Earth stood still: How do we know the Earth is spinning? The effect of Earth s rotation Day and night Wind and surface ocean currents What has the moon done for us lately? Moon facts and myths The tides on Earth 1

2 NZQA Information about this NCEA standard: S1.15 (AS 90954), Credits: 4, Level: 1, Internal Assessment This achievement standard involves demonstrating understanding of the effects of astronomical cycles on planet Earth. Achievement Criteria Achievement Achievement with Merit Achievement with Excellence Demonstrate understanding of the effects of astronomical cycles on planet Earth. Demonstrate in-depth understanding of the effects of astronomical cycles on planet Earth. Demonstrate comprehensive understanding of the effects of astronomical cycles on planet Earth. Explanatory Notes 1 This achievement standard is derived from The New Zealand Curriculum, Learning Media, Ministry of Education, 2007, Level 6. It is aligned with the Astronomical Systems achievement objective in the Planet Earth and Beyond strand, and the Nature of Science strand, and is related to the material in the Teaching and Learning Guide for Science, Ministry of Education, 2010 at 2 Demonstrate understanding involves describing astronomical cycles and the effects on planet Earth using information, visual representations, and data. 3 Demonstrate in-depth understanding involves explaining astronomical cycles and the effects on planet Earth using information, visual representations, and data. 4 Demonstrate comprehensive understanding involves explaining thoroughly links between astronomical cycles and the effects on planet Earth using information, visual representations, and data. It may involve elaborating, applying, justifying, relating, evaluating, comparing and contrasting, or analysing. 5 Astronomical cycles are: Spin of the Earth Orbit of Earth around Sun Orbit of Moon around Earth Effect of the Earth s tilt and the heating effect of the Sun. 6 Effects on planet Earth may be selected from: Day and night Seasons Changes of temperature during the day and night Seasonal changes at the North and South poles, latitude of New Zealand, Tropics of Cancer and Capricorn, and the Equator Formation and direction of winds in the Southern hemisphere - direction of surface ocean current flows in the Pacific Ocean Phases of the Moon Formation of tides Neap and Spring tides. 2

3 The Earth and its Sun and Moon are in a type of continual cosmic dance. We all know the Moon revolves around the Earth. The Earth, in turn, revolves around our Sun and rotates on its own axis. But did you know that without these astronomical cycles, life on Earth would probably not exist? In the next few weeks we are going to look at the profound effect these astronomical cycles have on the Earth. But let s begin with a quick quiz to find out what you already know. Below are some statements about the Earth, Moon and Sun and their interactions. Indicate whether you think each statement is a Fact (F) or a Myth (M). Statement 1. In the Northern Hemisphere water will always run down a drain in a clockwise direction. In the Southern Hemisphere it is always anti-clockwise. Fact / Myth 2. Winter is caused by the fact that the Earth is further away from the Sun. 3. Earth s spin on its own axis is slowing down. 4. The spin of the Earth is one of determining factors in the formation and direction of winds on the Earth. 5. The Moon is mainly responsible for the tides on Earth. 6. The tilt of the Earth is a factor in the formation of winds on Earth. 7. The phases of the Moon are caused by the Earth s shadow. 8. The same side of the Moon always faces the Earth. 9. The far side of the Moon (i.e. the side of the Moon not facing the Earth) is always dark. 3

4 We all know there are four seasons: spring, summer, autumn and winter. For summer we thing of hot weather and long days; and winter is cold with short days and long nights. In spring we expect to see flowers blooming and leaves coming out on the trees. In autumn the opposite happens, with leaves falling from the trees and temperatures cooling down. There are four key times in the year which mark the seasons. Autumn Equinox (21 March): marks the beginning of autumn in the southern hemisphere. On this day, the night and day are of equal length. Winter Solstice (21 June): the shortest day of the year. It marks the beginning of winter in the southern hemisphere. Spring Equinox (23 September): also known as the Vernal Equinox. It marks the beginning of spring in the southern hemisphere. Like the Autumn Equinox, on this day the night and day are equal length. Summer Solstice (21 December): the longest day of the year. It mars the beginning of summer in the southern hemisphere. But what causes the seasons? What do you think causes the seasons? Write your hypothesis or hypotheses in the space below. Try to be specific with your ideas and language. 4

5 Many people believe the seasons are caused by the Earth being further away from the Sun in winter than in summer. Is this one of the ideas you had? Let s test this hypothesis. The Earth s orbit of the Sun is not perfectly circular, it is elliptical. The diagram below shows the elliptical orbit of the Earth around the Sun. We can see that during one part of the year, the Earth moves closer to the Sun (called the perihelion). Six months later the Earth is at its furthest point from the Sun (called the aphelion). We know that the further you move away from the source of heat, the less heat you feel (and vice versa). If you are getting too hot, you move further away from the fire or the heater. If you are getting too cold, you might move a little closer. This is why some people believer that the seasons are caused by differences in the distance between the Earth and the Sun. 5

6 But there s a problem with this hypothesis. Look at the diagram again this time with dates and seasons included. 1. When is the Earth closest to the Sun? 2. When is the Earth farthest from the Sun? 3. What does this mean for the theory that the distance between the Earth and Sun is the cause of the seasons? In fact, the Earth s orbit around the Sun is nearly a perfect circle; it is only off by 4%. Astronomers have calculated that the difference in incoming solar radiation is only about 7% - not enough to be responsible for the changes in seasons. 6

7 So we have identified the first of our myths. The Earth s Tilt As the diagram below shows, the Earth s axis is on a tilt (or obliquity) of about 23.5 from vertical. In fact the Earth wobbles a bit, so the tilt varies from about 22 to This wobble is understood to be cyclical and gradual (i.e. it takes place over many thousands of years). But how does the Earth affect the season of the Earth? You are now going to do two different experiments to find out. 7

8 Now that you have done your first two experiments, let s take a quick quiz on vocabulary. Match the following terms with their correct definitions or explanations. The first one was been done for you as an example. Answer Term Definition F 1. Elliptical A. Another word for the tilt of the Earth s axis 2. Perpendicular B. Point in the Earth s orbit at which it is closest to the Sun 3. Aphelion C. Marks the beginning of spring 4. Orbit D. Point in Earth s obit at which it is furthest from the Sun 5. Winter Solstice E. To travel in a curved path around a larger body 6. Obliquity F. Shaped like a circle but with two slightly longer sides 7. Perihelion G. Shortest day of the year 8. Vernal Equinox H. Face-on; a 90 angle 8

9 For a long time in human history, most people believed that the Earth was the centre of the universe. They believed that everything the stars, the Sun, etc revolved around the Earth. We can understand why they thought this. Someone who looks up and sees the Sun, Moon and stars moving across the sky might easily conclude that these celestial bodies are moving around the Earth. However, as science advanced we discovered that the Earth is not the centre of the universe, and that the Earth actually revolves around the Sun. We have also discovered that the rotation of the Earth on its own axis is what causes the apparent movement of the Sun and stars across our sky. How do we know the Earth is spinning? How do we know for sure that the Earth really is spinning on its own axis? It certainly doesn t fell like we are spinning around! In 1851 a French physicist named Jean Bernard Leon Foucault set out to prove that the Earth rotates. He did this using a pendulum. 9

10 Many of you may have already seen a pendulum, like the one in the clock in the picture. A pendulum is a weight (called a bob) which is attached in such a way that it can swing freely under the influence of gravity. If there is no air resistance (friction), air currents, or other force which acts on the pendulum, it will swing back and forth along the same plane (i.e. in the same line) forever. If you looked at it from above, the pendulum would look kike that shown in Figure 3 below. Figure 3: If no forces other than gravity acts on it, a pendulum which starts moving in a North South direction will continue to do so forever. But Foucault found that what actually happens is that as time passes, the direction of the pendulum s line of swing changes relative to the floor (see Figures 4 and 5). We know the pendulum is not changing direction because no force other than gravity has acted on it. This means that the floor must be moving it is twisted around by the daily rotation of the Earth. 10

11 The effect of Earth s rotation In fact, every few years, an extra second (leap second) is added to a day. It s estimated that 400 million years ago, a day was 22 hours long and in 400 million years time, a day will be 26 hours long. So what would happen if the Earth were to stop spinning? Look at the list below. Put a tick next to those that you think would be affected if the Earth stopped spinning. If the Earth stood still, it would affect Day and night The seasons The formation and direction of winds on Earth The direction of surface ocean currents Formation of tides The Earth s climate The weather Food production Our survival on the planet 11

12 Day and night We all know that the spin of the Earth gives us day and night, and the heating and cooling that goes along with these. At any one moment, half of our planet faces the Sun (i.e. day) and the other half is in darkness (i.e. night). If the Earth were to stop spinning, then on any given day of the year, one half of the Earth would experience 24 hours of sun and the other half would be in darkness for 24 hours. Wind and surface ocean currents In New Zealand, wind and surface ocean currents have a major impact on our climate and weather. These in turn affect our physical environment and resources. Look at the map below of New Zealand. You will notice that New Zealand lies roughly between 34 S and 47 S. This puts us firmly in the middle of the weather system known as the roaring forties. Figure 6: Map of New Zealand 12

13 The Roaring Forties The roaring forties is the name given to the strong, steady prevailing westerly winds which blow between the latitudes of 40 S and 50 S. In the Southern Hemisphere there is very little landmass to slow these winds down and so they blow almost continuously (see Figure 7). These westerly winds carry warm air and wet weather to the west coast of New Zealand. The currents around New Zealand also have a major impact on the New Zealand climate, weather and physical environment. Warm currents from the tropical regions make New Zealand s climate 2 C warmer than it would be without these currents. When currents of warmer water meet colder currents, it forces nutrients to rise up from the ocean floor. Currents transport nutrients from Australia towards New Zealand s fishing grounds. The result is excellence fish production (and fishing) around New Zealand. As warmer currents move south and cool, moisture from the oceans evaporates and this brings the rains to New Zealand. This gives New Zealand its moist, mild climate. But what causes the winds the currents? To find out what causes the prevailing winds and currents for New Zealand, we need to look at what causes these on a global scale. Let s begin with wind. 13

14 Wind Wind is the movement of air in the atmosphere from on e place to another. The faster the air moves, the stronger the wind. Winds form part of a type of global air conditioning system which acts to balance temperature and air pressure around the world. What do you think causes the wind? Write your hypothesis in the space below. Something we investigated earlier can give us a clue as to the ultimate cause of wind. Earlier we discovered the Sun s heating effect differs at different latitudes on the planet (differential heating). Can you remember why? Write your explanation below. 14

15 Putting the pieces together Let s put thoughts in order so that you can understand how the differential heating of the Earth causes the wind. Put the following 4 statements in order by listing the numbers 1, 2, 3 and 4 in the table below. Order Statements and notes Air moves from an area of high pressure to an area of low pressure. This movement of air is wind. Hot air rises. Cold air sinks. So The hot air over the equatorial regions rises, resulting in an area of low pressure above the land or sea. The cold air over the poles sinks, resulting in an area of high pressure over the polar regions. Equatorial regions of the Earth are heated most. Polar regions of the Earth are heated least. So, putting this all together, that means that air (wind) should move in straight lines from the poles to the equator, as shown in the diagram of airflow to the right. However, the reality is a bit more complicated than this. The diagram below shows a simplified view of what actually happens. 15

16 Hot air rises along the equator and eventually reaches the troposphere, where it can rise no higher. As a result it spreads outwards towards the poles. As it spreads, it cools down and sinks back to the surface at about 30 degrees south and north of the equator. This sinking air produces areas of higher pressure around latitudes 30 S and 30 N. Some of this air moves back towards the equator. These are known as the Hadley Cells. The remaining air continues to move towards the poles. At around 60 S and 60 N, it meets cold air which is on its way form the poles to the equator. The warm air moving from the equator is forced up above this colder air, resulting in another band of low pressure. The air then moves back towards the equator. These are called Ferrell Cells. Finally, between 60 S and the South Pole, and 60 N and the North Pole, there are Polar Cells. These are responsible for the flow of air in the Arctic and Antarctic regions. The three circulation cells of the Hadley, Ferrell and Polar cells result in bands of high and low pressure across the surface of the Earth. But the air moving from high to low pressure does not flow in a straight north-south path. If it did, winds over New Zealand would be predominantly southerly, blowing from the colder southern pole towards the Equator. As we already know, this is not the case the prevailing wind for New Zealand is a westerly. Global wind patterns Rather than moving in a straight North-South path, wind moves in distinct patterns at different latitudes on our planet. Easterly winds dominate the flow pattern across polar regions. Westerly winds blow across the mid-latitudes (i.e. 35 S 65 S and 35 N 65 N). Easterly winds dominate the tropics. So why doesn t the wind blow North to South in the northern hemisphere and South to North in the southern hemisphere? What do you think causes the global wind patterns? Write your hypothesis or hypotheses in the space below. 16

17 You may have figured out that the rotation of the Earth has something to do with the direction of the prevailing global winds. Now you are going to do an experiment to find out exactly what the effect Earth s rotation has on the direction of winds. The Coriolis Effect You ve found that the Earth s rotation causes winds to be deflected from their intended paths. This is known as the Coriolis Effect. You found out that in the northern hemisphere, the Coriolis Effect deflects winds to the right of their intended path (i.e. clockwise). In the southern hemisphere, the deflection is to the left of the intended path or anti-clockwise. Does this mean it is true that in the northern hemisphere water will always run down a drain in a clockwise direction? And in the southern hemisphere water will always flow down anti-clockwise? The Coriolis Effect only has an effect on large-scale air movement in the atmosphere (wind) or water in the oceans (currents). It does not have any effect on small movements of water like that of bath water or water in sinks going down drains. Surface currents There are three key factors which play a role in the formation and direction of surface ocean currents. 1. Wind: Wind is the most important cause of surface ocean currents. Friction at the point where the ocean surface and wind meet cause the water to move in the direction of the wind. 2. The rotation of the Earth and the Coriolis Effect: The Coriolis Effect plays an important role in determining the direction of surface ocean currents. It has the same effect on the ocean currents as it does on the winds in the atmosphere. 3. Land mass: Major land masses also have an impact on the direction and surface ocean currents. When an ocean current reaches a land mass, it is deflected by that land. Let s look at how these factors affect the surface ocean currents around New Zealand. The diagram to the right shows a simplified view of the currents around New Zealand. 17

18 In the previous diagram we can see the very warm South Equatorial Current is bent southwards as a result of the Coriolis Effect and by the land mass. The current then moves south along the east coast of Australia where it is called the East Australian Current. At around 30 S, Australia s most eastern most point, this current splits in two. One part is redirected eastwards as a result of the Coriolis Effect. The other part of the current continues on to move south down the east coast of Australia until it meets the cold water of the West Wind Drift south of Tasmania. At this point it cannot move any further south. The current is then deflected eastwards as a result of the Coriolis Effect. Once it reaches New Zealand western coast it is deflected northwards as a result of the land mass and the Coriolis Effect. Many people look up at the night sky and are struck by the beauty of the Moon. Yes, the Moon is nice to look at, but is that all it offers us on planet Earth? In this section we look at how the orbit of the Moon around the Earth has a major impact on life on Earth. Let s first look at a few facts and myths about the Moon. Moon facts and myths This is because it takes the Moon the same amount of time to orbit the Earth as it does to complete one rotation on its own axis. The Moon rotates on its own axis approximately every 28 days, and orbits the Earth approximately every 28 days as well. This means that the same side of the Moon always faces the Earth. Does the same side of the Earth always face the Sun? Why or why not? 18

19 Some people think that the side of the Moon not facing the Earth is always dark. But if you think about it, this is clearly no possible. Look at Figure 1 which shows the Earth, Moon and Sun. The picture is not to scale, but it clearly shows the relative positions of all 3 for the New Moon and Full Moon. You can see that the far side of the Moon is not dark all of the time. Both sides of the Moon get an equal amount of light as it orbits Earth; we just never see it because from Earth we can only see one side of the Moon. When the Moon is between the Sun and Earth we see a New Moon. When the Earth is between the Sun and the Moon we see a Full Moon. The only time Earth s shadow affects our view of the Moon is during a lunar eclipse, when a full Moon passes through Earth s shadow. 19

20 The Moon has a very important effect on the Earth because it is one of the key factors in the formation of the tides. The tides on Earth Tides on Earth have an important impact on the coastal environment and organisms. Tides create an area of rocky coast where a wide range of specialized organisms can evolve (e.g. limpets, barnacles, oysters, etc). Tides promote the development of a very rich habitat which attracts and supports large numbers of fish. They do this by creating currents which spread surface plankton and nutrients from the sea bed. This provides food for organisms which feed on plankton and the fish which feed on them. The currents created by tides help to minimize the impact of pollution and runoff from the land by mixing these up and moving them from the coast. The Moon and tides A tide is the rise and fall of the water caused primarily by the gravitational force of the Moon on the oceans (and other very large bodies of water). The surface of the oceans on the side of the Earth facing the Moon is pulled towards the Moon. This causes the water to pile up, resulting in a tidal bulge, or high tide. As a result of centrifugal forces, there is another tidal bulge on the opposite side of the Earth. Between these two high tides are low tides: the lowest levels of the oceans. 20

21 Most areas experience two high and two low tides approximately every 24 hours and 50 minutes or just over one day. The Earth does a full rotation on its own axis in 24 hours. So why do you think it takes 24 hours and 50 minutes for there to be two high and two low tides? Write your hypothesis or hypotheses in the space below. Hint: How does the Earth move over a 24 hour period? How does the Moon move in its orbit around the Earth over the same period? The Sun s role in the tides The tides on Earth are also affected by the Sun. The Sun exerts a gravitational force on the Earth too, although it this is much smaller than that of the Moon. Twice a month, the Earth, Moon and Sun are in a line, the Moon and Sun s gravitational pull on the Earth combine and the tides are higher than at other times. The low tides are therefore also at their lowest. These are called spring tides, when the difference between low and high tide is at its greatest. When the Sun and Moon are at right angles, or 90, to the Earth their gravitational pulls on the Earth compete. At such times the high tides are not very high. Therefore, the low tides do not fall very much. These are called neap tides, when there is the smallest difference between low and high tide. Phases of the moon and the tides Is there any link between the phases of the Moon and the tides? You can do an activity to find out to finish off this unit. 21

22 In this course we looked at the effect the following astronomical cycles have on the Earth. 1. The Earth s rotation on its own axis 2. The Earth s tilt and the heating effect of the Sun 3. The Earth s orbit around the Sun 4. The Moon s orbit around the Earth The table below lists some of the effects which these astronomical cycles have. For each effect indicate which astronomical cycle, or cycles, is responsible. Just write the number of the astronomical cycle in the right-hand column. The first one has been done for you as an example. Effect Astronomical Cycle Day and night 1 The seasons Changes of temperature during the day and night Formation and direction of winds Formation and direction of surface ocean currents Phases of the Moon Formation of tides In this course you have investigated the astronomical cycles of the Earth, Sun and Moon and the effect these have on our planet. You have discovered that: these cycles and their effects are interlinked, that small changes to these cycles would have a profound effect on our planet. 22