CSS Forums - Introduction To The Earth

[B][CENTER][SIZE="4"]INTRODUCTION TO THE EARTH[/SIZE][/CENTER][/B]

The Earth is the third planet from the Sun in our solar system.it is the planet we evolved on and the only planet in our Solar system that is known to support life.

[B]SIZE[/B]

The Earth is about 7,926 miles (12,756 km) in diameter.The Earth is the 5th largest planet in our Solar system ( after Jupiter,Saturn, and Neptune).

Eratosthenes (276-194 BC) was a Greek scholor who was the first person to determine the circumference of the Earth.He compared the mid summer's noon shadow in deep wells in Syene( now Aswan on the Nile in Egypt ) and Alexandria.He properly assumed that the Sun's rays are virtually parallel(since the sun is so far away).knowing the distance between the 2 locations,he calculated the circumference of the earth to be 250,000stadia.Exactly how long a stadia is unknown,so his accuracy is uncertain,but he was very close.He also accurately measured the tilt of the Earth's axisand the distance to the sun and and moon.

[B]THE MOON[/B]

The Earth has one Moon.The diameter of the Moon is about one quater of the diameter of the Earth.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.

[B]MASS,DENSITY AND ESCAPE VILOCITY[/B]

The Earth's mass is about 5.98 into 10 is to power 24kg.The Earth has an average density of 5520 kg/m3 ( water has the density of 1027kg/m3).Earth is densest planet in our solar system.To escape the Earth's gravitational pull, an object must reach a velocity of 24,840 miles per hour (11,180 m/sec).

[B]LENGTH OF A DAY AND YEAR ON EARTH[/B]

Each day on Earth takes 23.93 hours (that is,it takes the Earth 23.93 hoursto rotate around its axis once - this is a sidereal day).Each year on Earth takes365.26 Earth days ( that is,it takes the Earth 365.26 days to orbit the Sun ).The Earth's rotation is slowing down very slightly over time, about one second every 10 years.

[B]THE EARTH'S ORBIT[/B]

The Earth's orbits,on average,93 million miles ( 149,600,000 km ) from the Sun.This distance is defined as one Astronomical Unit
(AU).The Earth is closest to the Sun ( this is called perihelion )around january 2 each year ( 91.4million miles = 147.1million km ); it is farthest away from the Sun ( this is called aphelion ) around July 2 each year ( 94.8 million miles =152.6 million km ).

[B]THE EARTH'S AXIS TILT AND THE SEASONS[/B]

The Earth's axis is tilted from perpendicular to the plane of ecliptic by 23.45 degree.This tilting is what gives us the four seasons of the year. Summer,Spring,Winter and Autumn.Since the axis is tilted, diffrent parts of the globe are oriented towards the Sun at different times of the year.This affects the amount of sunlight each recieves.

[B]SPEED[/B]

At the equator, the Earth's moves 40,000 km in 24 hours.That is a speed of about 1040 miles/hr ( 1670 km/hr ).This is calculated by dividing the circumference of the Earth at the equator ( about 24,900 miles or 40,070 km ) by the number of hours in a day.As u move toward either pole, this speed decreases to almost 0 ( since the circumference at the extreme latitudes approaches 0 ).The Earth revovles around the Sun at a speed of about 30 km/sec.This compares with the Earth's rorational of approximately 0.5 km/sec.( at the middle latitudes - near the equator ).

[B]TEMPERATURE ON EARTH[/B]

The temperature on Earth ranges from between - 127 degree F to 136 degree F (-88 degree C to 58 degree C; 185K to 311K ).The coldest recorded temperature was on the Earth continent of Antartica ( Vostoc in July,1983 ).The hottest recorded temperature was on the continent of Africa ( Libya in September, 1922 ).
The green house effect traps heat in our atmosphere.The atmosphere lets some infra red radiation escape into space; some is reflected back to the planet.

The green house is an increase in the temperature of a planet as heat energy from sunlight is trapped by the gaseous atmosphere.Excess carbon dioxideand water vapour increase this global warming effect.

Solar Energy (sunlight) is short - wavelength radiation which easily penetrates the Earth's atmosphere and warms the Earth; only about one quarter of incoming sunlight is reflected by the atmosphere.The warmed Earth emits long-wavelength radiation (infra red waves or heat energy) back into space; these longer waves are mostly reflected back to Earth by the atmosphere.

The size of the atmosphere in the illustration above is greatly exaggerated in orderto show the green house effect.Mostof the Earth's atmosphereis within 10 miles ( 16 km ) of the Earth's surface.

[B]ATMOSPHERE[/B]

The Earth's atmosphere is a thin layer of gases that surrounds the Earth.It iscomposed of 78% nitrogen,21% oxygen, 0.9% argon, 0.03% carbon dioxide and trace amounts of other gases.

The atmosphere was formed by planetary degassing,a process in which gases like carbon dioxide, water vapor, sulphur dioxide and nitrogen were released from the interior of the Earth from volcanoesand other processes. Life forms on Earth have modified the composition of the atmosphere since their evolution.