Statistics | Atmosphere |
Mass (kg) . . . . . . . 5.97e24
Mass (Earth = 1) . . . . . 1.000
Equatorial radius (km) . . . . 6,378
Equatorial radius (Earth = 1) . . 1.000
Mean Density (gm/cm^3) . . . . 5.52
Rotational period (hours) . . . 23.9345
Tilt of axis (degrees) . . . . 23.45
Nitrogen . . . . . . . 78%
Oxygen . . . . . . . . 21%
Carbon Dioxide . . . . . . 0.03%
Water Vapor . . . . . . . up to 4.0%
The Earth's hydrosphere, or water layer, is what makes our planet
unique in the solar system. Approximately three quarters of Earth's
surface is covered by liquid water. Some of this water evaporates
and condenses around dust, salt, or pollen grains that are blown into
the atmosphere. These condensation nuclei are the beginnings of our
Cloud are classified by their color, shape, and altitude. Most clouds
consist of condensed water vapor - in other words, liquid water. Clouds
that form very high in the sky, however, tend to form from ice crystals.
These clouds are cirrus clouds. They are very thin, wispy clouds.
Clouds play an important role for our terrestrial readers. They
supply rain and snow and help keep in the infrared heat that is radiating
from earth. Carbon dioxide also helps trap the heat and keep it in
the atmosphere. This is called the greenhouse effect. Clouds and carbon
dioxide in our atmosphere help moderate the daily temperature fluctuations
on Earth. Daily temperature changes are at an extreme in deserts.
The difference between the hot days and cool nights in these areas
is because there are very few clouds and little water vapor in the
air to keep in the heat.
Usually you can see a sharp line of clouds in satellite images.
This line is called a front, and is a boundary between different types
of air (for example: hot/dry meeting cool/moist). The passing of a
front usually means a change in weather.
Since the orbit of the Earth around the sun is almost circular,
the distance from the sun is nearly constant and is NOT a factor
in causing seasons on Earth. Seasons on earth result because Earth
is tilted on an axis. Since it is tilted, one pole will point toward
the sun as it revolves in its orbit. When the North Pole is tilted
toward the sun it is summer in the northern hemisphere. At this time
the North Pole receives 24 hours of daylight. The South Pole is in
darkness for 24 hours. The sun's direct rays are shining at 23.5 degrees
latitude, the Tropic of Cancer. On the first day of summer the sun
is directly overhead here.
The first day of summer for the northern hemisphere is called the
summer solstice. It occurs June 21 or 22. This has the longest number
of daylight hours in the North. Summer officially lasts until the
first day of autumn.
The first day of autumn for the northern hemisphere is called the
autumnal equinox. It occurs September 22 or 23. At this time the sun
is directly overhead at the equator, and day and night are equal length.
Autumn officially ends in December.
The first day of winter for the northern hemisphere is called the
winter solstice. It occurs December 21 or 22. This day has the shortest
number of daylight hours in the North. The sun at this time is shining
overhead at 23.5 degrees south latitude, at the Tropic of Capricorn.
Winter ends in March.
The first day of spring for the northern hemisphere is called the
vernal equinox. Because of the tilt of Earth and its revolution around
the sun, the sun's direct rays are once again at the equator and day
and night are equal length. This occurs March 20 or 21.