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"Spheres, spheres,
spheres, spheres, spheres! The universe is full of spheres! A marble
is a sphere. A basketball is a sphere. A balloon is a sphere--well,
almost. The Sun is a great, big, giant, super-colossal, boiling
hot sphere!
Even Earth is a huge
sphere. In fact, you can think of Earth as a whole bunch of spheres,
one inside the other, something like the colored layers inside a
jawbreaker. From the inside out, Earth's spheres are:
The Lithosphere
("rock sphere") is the ground you are standing on and
the whole inside of Earth.
The Hydrosphere
("water sphere") includes all of the rivers, lakes and
oceans of Earth.
The Cryosphere
("icy cold sphere") is the frozen part of Earth: the glaciers,
icebergs at sea, and the huge icecaps in Greenland and Antarctica.
The
Biosphere
("Life sphere") includes all
living things: the trees in the park,
the birds in the air, the fly on your
wall, the viruses that make you sick,
your pets, and even you and all your friends!
The
Atmosphere
("Air Sphere") is the envelope
of air that surrounds the whole Earth.
The
Exo- or Celestial
Sphere ("Outside or heavenly
sphere") includes the whole universe
beyond the top of the atmosphere--the
Sun, Moon, and stars, as well as the asteroids
and the little bits of dust that make
meteors when they hit the atmosphere.
OK, so Earth is made
of a bunch of spheres. But are the "spheres" really exact
spheres?
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