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Earth, our home planet, is the only planet
in our solar system known to harbor life - life that
is incredibly diverse. All of the things we need to
survive are provided under a thin layer of atmosphere
that separates us from the uninhabitable void of space.
Earth is made up of complex, interactive systems that
are often unpredictable. Air, water, land, and life
- including humans - combine forces to create a constantly
changing world that we are striving to understand.
Viewing Earth from the unique perspective
of space provides the opportunity to see Earth as a
whole. Scientists around the world have discovered many
things about our planet by working together and sharing
their findings.
Some facts are well known. For instance,
Earth is the third planet from the Sun and the fifth
largest in the solar system. Earth's diameter is just
a few hundred kilometers larger than that of Venus.
The four seasons are a result of Earth's axis of rotation
being tilted more than 23 degrees.
Oceans at least 4 km deep cover nearly
70 percent of Earth's surface. Fresh water exists in
the liquid phase only within a narrow temperature span
(0 degrees to 100 degrees Celsius). This temperature
span is especially narrow when contrasted with the full
range of temperatures found within the solar system.
The presence and distribution of water vapor in the
atmosphere is responsible for much of Earth's weather.
Near the surface, an ocean of air that
consists of 78 percent nitrogen, 21 percent oxygen,
and 1 percent other ingredients envelops us. This atmosphere
affects Earth's long-term climate and short-term local
weather; shields us from nearly all harmful radiation
coming from the Sun; and protects us from meteors as
well - most of which burn up before they can strike
the surface. Satellites have revealed that the upper
atmosphere actually swells by day and contracts by night
due to solar activity.
Our planet's rapid spin and molten nickel-iron
core give rise to a magnetic field, which the solar
wind distorts into a teardrop shape. The solar wind
is a stream of charged particles continuously ejected
from the Sun. The magnetic field does not fade off into
space, but has defi- nite boundaries. When charged particles
from the solar wind become trapped in Earth's magnetic
field, they collide with air molecules above our planet's
magnetic poles. These air molecules then begin to glow
and are known as the aurorae, or the Northern and Southern
Lights.
Earth's land surfaces are also in motion.
For example, the North American continent continues
to move west over the Pacific Ocean basin, roughly at
a rate equal to the growth of our fingernails. Earthquakes
result when plates grind past one another, ride up over
one another, collide to make mountains, or split and
separate. These movements are known as plate tectonics.
Developed within the last 30 years, this explanation
has unified the results of centuries of study of our
planet, long believed to be unmoving.
From the vantage point of space we are
able to observe our planet globally, as we do other
planets, using similar sensitive instruments to understand
the delicate balance among its oceans, air, land, and
life.
Related Links:
Source: NASA
Last Updated : 08.20.2003
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Distance from
the Sun:
(Semimajor axis of orbit)
149,597,890 km
1 A.U.
Radius:
6,378.14 km
(1 of Earth's radius)
Equatorial Circumference:
40,000 km
(C = 2*p*r)
Mass:
5.9742 x 1027 g
Density:
5.515 gm/cm3
Surface Gravity:
980 cm/s2
Escape Velocity:
11.18 km/s
Sidereal Rotation
Period:
0.99726968 day
Sidereal Orbit
Period:
1.0000174 sidereal years
Mean Orbit Velocity:
29.7859 km/s
Orbit Eccentricity:
0.01671022
Orbit Inclination:
0.00005 degree
Equatorial Inclination:
23.45 degrees
Mean Surface
Temperature:
288 to 293 K
Atmospheric
Temperature (at level with pressure = 1 bar):
288 K
Major Atmospheric
Constituents:
N2, O2
Natural Satellites:
1. Moon
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