The Earth

The Earth | Geography

The earth is the only known planet which provides life on it. The earth is the largest of the inner planets. It takes 23 hours 56 minutes and 4.091 seconds to rotate on its axis and 365 days, 5 hours and 48 minutes to revolve around the sun. The earth is 231/2° tilted on its axis and thus makes 661/2° angle. Earth is known as the blue planet.

The earth is a sphere, at the north pole, the pole star can always be observed at 90° degrees in the sky. As one travels southwards, the angle of pole decreases. At the equator the angle becomes zero degree. This observation proves that the path of travel is an arc of a circle. 

Earth has all the essential elements like carbon dioxide, hydrogen, nitrogen and oxygen which supports life. It is neither too hot nor too cold. It has right temperature ranges. 

The earth has a lot of water in the form of lakes, rivers, oceans and seas. 

It is protected from UV rays by the ozone layer cover present in the stratosphere.

Composition of elements

Oxygen46.5%
Silicon27.72%
Aluminum8.13%
Iron5.01%
Calcium3.63%
Sodium2.9%
Potassium2.1%
Magnesium2.09%
Others0.5%

Effects of tilted axis on day and night

Rotation of earth on its tilted axis causes the change in the length of days and nights throughout the year

Perihelion:

It is the nearest point to the sun. It happens on 3rd January at a distance of 147 million kilometre.

Aphelion:

It is the farthest distance to the sun at a distance of 152 million kilometre on 4th July.

Solstice:

A solstice is an event occurring when the Sun appears to reach its most northerly or southerly.

Summer solstice: on June 21, the sun is overhead on the tropic of cancer (231/2°N). On this day the northern hemisphere has the longest day and southern hemisphere having the shortest day. 

Winter solstice: on December 22, the sun is overhead on the tropic of Capricorn(231/2°S). On this day the southern hemisphere has the longest day and the northern hemisphere having the shortest day.

Equinoxes:

Two days in a year when day and night are equal throughout the world are equinoxes. The vertical equinox occurs on March 21 and it is also called the spring equinox. The autumnal equinox occurs on September 23. On these dates the sun lies directly above the equator.

Midnight sun:

This phenomenon is observed in the Arctic and Antarctic zones. Norway is the place of midnight sun where the sun is continuously visible between May and July.

Eclipses:

An eclipse occurs when the sun, the earth and the moon lie in a straight line. Generally, seven eclipses take place every year.

Solar eclipse: it occurs between sunrise and sunset on the new moon. The moon lies between the sun and the Earth.

Lunar eclipse: the lunar eclipse takes place when the earth comes in between the sun and the moon so that the shadow of earth is cast on the moon. A lunar eclipse takes place on a full moon.

Longitudes and latitudes:

The north to south lines on the globe are known as longitudes and the east to west lines on the globe are known as latitudes. Longitude causes time to differ at different places on the earth. Latitude of a place Tell us about the climate of the place in general terms, and the related vegetation and animal life. Latitude along with a longitude enables us to find the exact location of a place on the earth.

There are 180 parallel latitudes. The equator at 0° is the largest latitude that can be drawn on the globe. Each parallel line of a latitude is a circle. The circle becomes smaller towards the pole. The distance between two parallel latitudes are always equal.

There are 360 meridians of longitude. The prime meridian is a longitude of 0°. Each meridian of longitude is a semi circle. All meridians are equal in length. The distance between any two meridians is not equal. The longitude (meridian) passing the royal astronomical observatory in Greenwich, England, is the one chosen as zero longitude.

Longitude and time

The earth takes approximately 24 hours to complete one rotation. For each 1° of longitude towards the east, a time of four minutes has to be added. For each 1° of longitude towards the west, a time of four minutes has to be subtracted.

In India, the longitude of 82°30’E, passing through the area near Allahabad is considered the standard meridian. This is known as the Indian standard time. IST is five hours thirty minutes ahead of GMT.

International date line

The line at which a day is lost or gained is called the international date line. It is a line on the globe approximately along the 180° meridian of longitude.

Torrid Zone

The region between the tropic of cancer and the tropic of Capricorn receives direct rays of the sun particularly throughout the year. This area receives maximum heat and is called the torrid zone.

Frigid zone

Near the pole region, the rays of the sun are very slanting and so it is cold. The regions of Arctic and Antarctic circles are called the frigid zone.

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