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1. Measuring the
size of Earth
It is next to impossible to measure the size of the
Earth using a tape measure- it is just too big. We can
measure the size of the Earth accurately with the
help of mathematics. One way of doing it is to look at
a star from two places on Earth. If the distance
between these two places is known, we can get
answers to how big the Earth really is.
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2. Measuring thesize of Earth
Satellites which are used for mapping is another way
to measure the size of the Earth. These satellites
keep a watch on Earth from 35,900 kilometers away
in space. They can measure the angle between
themselves and the two places on Earth. Once
scientists know what these angles are, it is used to
get a measure of the Earth's radius; the distance
from the center of the Earth to its surface. The
radius of the circle will help you determine its
circumference.
35,900 kilometersi
17.4
R
MEASURING THE EARTH FROM A SATELLITE
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3. The Greek scholar Eratosthenes found the
circumference of the Earth by studying the shadow
made by a tower in Alexandria, Egypt. He measured
the angle that the shadow made at noon on the
longest day of the year. He knew that on the same
day at the same time in Syene, the sun was at its
highest point. It shone straight down into a well, so it
must be directly overhead.
HOW ANCIENT GREEKS MEASURED THE EARTH
Measuring thesize of Earth
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4. The angle Eratosthenes measured at Alexandria was
7.2 degrees, or a fiftieth of a circle. So, he multiplied
the distance between Syene and Alexandria by 50 to
get the size of the Earth. He found that it was
about 40,000 kilometers around.
Measuring thesize of Earth
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5. INTERESTING FACTS
Measuring thesize of Earth
In the 6th century BC, Pythagoras claimed that the
Earth is round because both the sun and moon were.
It was Eratosthenes however in the 3rd century BC
whose estimate came very near the 40,075
kilometers, now known to be the circumference of
the planet at the equator.
Today's sophisticated and advanced equipment
shows that the Earth is 42 kilometers thicker at the
equator than around the poles.
40,075 kilometers
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6. PROJECT
Measuring thesize of Earth
The Greek scholar Eratosthenes was known for a few
other discoveries. What are they?
Eratosthenes made use of which other great
scholars works while discovering the size of the
Earth?
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