The Earth is in an orbit that is nearly CIRCULAR around the Sun. The radius of this orbit is 150 million km (which is, of course, the distance to the Sun.) and it takes a YEAR (365¼ days), for the Earth to complete ONE orbit, to fit this into the calendar we have 365 days for three years and then 366 days for a leap year. The Earth SPINS rapidly about its N-S axis; each rotation takes one DAY. Because of this spin, it looks as if the Sun moves across the sky taking 24 hours to go right round the Earth. In fact, the Sun stays still and it is the spin of the Earth that makes us think that the Sun moves.
The earth revolves at a thousand miles per hour, it is enough to make you dizzy, is this true if you stand
a) On the North Pole?
b) On the Equator?
The Poles and the Tropics
The diagram shows rays from the Sun . You can see that the Sun's heat and light rays strike the EQUATOR, directly and not inclined at an angle. This is why it is so HOT in countries near the equator. At the North and South Poles, the rays from the Sun SKIM across the Earth at a very SMALL angle; hardly any heat hits the Earth in these regions and that is why the Arctic and Antarctic regions are so cold.
Rays from the Sun in March and September (The Suns rays travel from left to right on the diagram below.)
The N-S axis of the Earth is INCLINED at an angle of about 23 degrees to the Earth's orbit around the Sun.
This means that there are a few months of the year when the North Pole is inclined towards the Sun (as in the diagram); the Sun shines down on the NORTHERN Earth for many hours of the day and it is SUMMER. Of course, the SOUTHERN Earth is facing away from the Sun and it is WINTER there.
The Sun is only the nearest star to the Earth. At night we can see millions of stars that are much further away; they SEEM to rotate because the Earth is spinning. It takes 24 hours for a particular star pattern to complete one rotation.
CAREFULLY READ THE PASSAGE ABOVE THEN ANSWER THE FOLLOWING QUESTIONS:-
1. What is the distance from the earth to the sun?
2. How long does it take the earth to go once around the sun?
3a. How many days are there in a year?
b. How many days are there in a leap year?
c. Explain why we have an extra day once every four years
d. Can you find out what happens each century, and why the year 2000 is special?
The real year is 365.25636 days.
4. The diagram shows a view of the Earth looking down on the North Pole.
Copy the diagram and use thefact that the Sun rises in the East to show the direction that
the Earth rotates.
5. Explain why the weather in Britain is warmer than in the Arctic but cooler than in Africa.
6. The diagram, on the next page, shows the Earths' orbit around the Sun with the Earths' position indicated on
a. December 21st
b. March 21st
c. June 21st
d. September 21st
Try this out with a globe and a light, tilt the globe to about
23 degrees and look at the day and night shadows on the globe.
a. Explain why the shortest day of the year occurs on December 21st
b. On which dates does the length of daylight equal exactly 12 hours?.
c. Why is June 21st called "Midsummer's Day"?
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