F4 SHAPE OF THE EARTH

SHAPE OF THE EARTH

In old days, earth was considered to be a flat disc with steep edges.
All heavenly bodies revolved around the Earth.
Babylonians thought- earth was circular in shape & surrounded by river Okeanos .
Ancient Indians – earth was flat with a huge mountain in the middle.
Aryabhatta , famous Indian astronomer, believed Earth was spherical in shape and rotated on its axis.
In Europe, Greek philosopher Pythagoras and Aristotle were first to state that Earth was spherical in shape. Considerable opposition to this view.
Now we have convincing evidence from man’s landing on the Moon that the Earth is spherical in shape, the evolution of this idea may be considered briefly.

PROOFS FOR SHAPE

LUNAR ECLIPSE:





The earth casts a shadow on the moon during a lunar eclipse. This shadow is always semi-circular in shape .







SUNRISE AND SUNSET: The fact that the time of sunrise varies from place to place on the Earth proves that the Earth is not a flat disc.
If the earth was flat, all places on the earth would have sunrise and sunset at the same time.





Circumnavigation



If we travel around the earth without changing the direction, we arrive at the place we started from.
As the earth is spherical in shape, it is possible to circumnavigate the earth.
Magellan’s crew was first to go round the earth in a ship and complete the voyage without encountering a sharp edge.
Now aircrafts make many trips round the world on scheduled flights.










SIGHTING A SHIP:






When a ship approaches the shore, a person standing on the shore can see the smoke at first and then the chimney and then the ship as a whole.

ARTIFICIAL SATELLITES:










The photographs of the earth & other planets sent by the artificial satellites prove that the earth is round.Aerial photographs from space show earth spherical. Astronauts have taken pictures of earth from moon showing its spherical shape

SHAPE OF THE EARTH

Now – not a perfect sphere.
Flattened at the poles & bulging at the equator
Named ‘geoid’.
At equator diameter measures 12,756 km
Poles the diameter is 12,714 k.m. giving a difference of 42km.

Earth is geoid in shape

SIZE OF THE EARTH

Average diameter is about 12,735 km.
Four planets – Mercury, Venus, Mars and Pluto (?) are smaller than the Earth.
Others are larger
Early attempt made to estimate the size in 3rd century BC by Greek philosopher called Eratosthanes.