The Earth and the moon. Photo taken by NASA's Galileo mission in 1990.
The Earth is the third planet from the Sun in our Solar System. It is the planet
we live on and the only planet in our Solar System that is known to support
life.
The Earth is about 12,756 km in diameter. The Earth is the fifth-largest planet
in our Solar System (after Jupiter, Saturn, Uranus, and Neptune).
The Earth and the moon. Photo taken by NASA's Galileo mission in 1990. |
The moon may have once been a part of the Earth; it may have been broken off the Earth during a catastrophic collision of a huge body with the Earth billions of years ago.
MASS, DENSITY, AND ESCAPE VELOCITY
The
Earth's mass is about 5.98 x 1024 kg.
Earth is the densest planet in our Solar System.
To escape the Earth's gravitational pull, an object must reach a velocity of
11,180 m/sec.
LENGTH OF A DAY AND YEAR ON EARTH
 Earth rising over the moon. Photo taken by NASA's Apollo 8 mission. |
Each day on Earth takes 23.93 hours (that is, it takes the Earth 23.93 hours to
rotate around its axis once). Each year on Earth takes 365.26 Earth days (that
is, it takes the Earth 365.26 days to orbit the Sun once).
THE EARTH'S ORBIT
 Label the aphelion (farthest point in orbit) and perihelion (closest point in orbit) of a planet in orbit. |
On average, the Earth orbits, 150 000 000 km from the Sun. The Earth is
closest to the Sun (this is called perihelion) around January 2 each year (147.1
million km); it is farthest away from the Sun (this is called aphelion) around
July 2 each year (152.6 million km). The Earth has an orbit that
is close to being circular.
THE EARTH'S AXIS TILT AND THE SEASONS
The
Earth's axis is tilted from perpendicular to the plane of the ecliptic by 23.45°.
This tilting is what gives us the four seasons of the year: Summer, Spring,
Winter and Autumn. Since the axis is tilted, different parts of the globe are
oriented towards the Sun at different times of the year. This affects the amount
of sunlight each receives.
SPEED
At
the equator, the Earth's surface moves 40,000 kilometers in 24 hours. That is a
speed of about 1670 km/hr. As you move toward either pole, this speed
decreases to almost zero (since the circumference at the extreme latitudes
approaches zero).
The Earth revolves around the Sun at a speed of about 30 km/sec. This compares
with the Earth's rotational speed of approximately 0.5 km/sec (at middle
latitudes - near the equator).
TEMPERATURE
ON EARTH
The temperature on Earth ranges from between -88°C to 58°C. The coldest
recorded temperature was on the continent of Antarctica (Vostok in July, 1983).
The hottest recorded temperature was on the continent of Africa (Libya in
September, 1922).
ATMOSPHERE
The Earth's atmosphere is a thin layer of gases that surrounds the Earth. It is
composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and
trace amounts of other gases.