www.yahoo.com
"Our planet Earth (with a mass of
5.97x10^24) rotates on its axis once a day,
and orbits the Sun once a year at a distance of about 93 million miles
(150 million km). From the surface of the planet, the sky appears
to spin around the Earth once every day, while the Sun seems to move
around the sky against the background stars once a year. Although
close to a perfect circle, Earths orbit is in fact elliptical
(oval). This means it is 3 million miles (5 million km) closer to
the Sun in January than in July." The
Way the Universe Works, by
Robin Kerrod and Giles Sparrow
The Moon
"The Moon has been orbiting Earth for some 4.5 billion years. Its
large size ( with a mass of 7.35x10^22) and proximity to Earth (just
384 km away) mean that it has some important
effects on its parent planet. The Moon causes strong tides in
Earth's oceans, and may even protect us from impacts from space." The
Way the Universe Works, by
Robin Kerrod and Giles Sparrow
The Sun
"The Sun is the Nearest star to Earth. At a distance of 150 km,
it is hundreds of thousands of times closer to us than the next nearest
star. Like other stars, the Sun is a great globe of
intensely hot gases. Measuring about 870,000 miles (1.4 million
km) in diameter, it is 109 times larger than Earth and contains 750
times more matter than all the other bodies in the Solar System (its
total mass is 1.99x10^30)." The
Way the Universe Works, by
Robin Kerrod and Giles Sparrow
Orbiting Worlds
"Everything in the Solar System is in orbit
around something else- a legacy from the way the Sun and the planets
collapsed from a spinning gas cloud billions of years ago.
Planets, asteroids, and comets orbit the Sun, while rings and moons
orbit their parent planets. An orbit is any path through space
where an object's inertia- its tendency to travel in a straight line-
is perfectly balanced against the pull of gravity from a more massive
object. This is why objects in orbit do not simply fly off into
space or fall directly toward whatever they are orbiting. Natural
orbits are very rarley circular, and the closer a Solar System body
comes to the Sun, the faster it must move to keep in a steady
orbit. The result is that most of these objects have orbits in
the form of ellipses (ovals)." The
Way the Universe Works, by
Robin Kerrod and Giles Sparrow
The Pull of Matter
"Every
bit of matter exerts a force of
attraction because of its mass- the force of gravity. The greater
the mass, or the amount of matter in a body, the greater the
attraction. Gravity keeps the Moon circling Earth, it keeps Earth
and other plantes circling the Sun, it keeps the Sun circling the
Galaxy, and so on. We might think, therefore, that gravity is a
very powerful force, but it is not. It is actually the most
feeble of all the four fundamental forces- but it acts over much
greater distances than all the others."
The Way the Universe
Works, by Robin
Kerrod and Giles Sparrow
The gravity of Jupiter, a
giant planet, keeps a swarm of moons circling around it. www.yahoo.com
