The earth when viewed from space looks like a sphere. However, it has been found that the earth is not a perfect sphere as earth's Equatorial Diameter is more than the Polar Diameter. The difference between the Equatorial Diameter and the Polar Diameter is about 43,524 meters or 43.5 kilometers. Hence, the Earth could not be called a perfect sphere and is instead called a 'Geoid'.
The bulge at equator and flattening at the poles is caused by the 'Centrifugal Force' produced by the rotation of the Earth along its axis. The flattening and bulging causes the equatorial and polar diameters to differ.
Earlier it was believed that earth is a flat and if one ventures too far one will fall down from its edge. But now we know that earth is not flat but instead spherical in shape. How do we know that earth is spherical?
The earth being spherical does not have corners which could be taken as reference points to determine location of a place. Hence, we divide the earth into a grid using a series of vertical and horizontal imaginary lines and these are used to determine the location of a point on earth’s surface.
If we know G.M.T., to find local time, we merely have to add or subtract the difference in the number of hours from the given longitude.
Solar and Sidereal Time
The system in which we measure time is based on the concept of the solar day. It can be defined as the average time period required for the successive passages of the sun over a given meridian, and it is exactly 24 hours. This is known as the mean solar day. On the other hand, the time required for a 360 rotation of the earth, causing a given star in the sky to return to the same position in relation to the earth is known as the Sidereal day, and this period is about four minutes less than the mean solar day.
meridian of 82-1\2o E passing through Allahabad, which is situated roughly in the middle part of the country.
INTERNATIONAL DATE LINE
What Is the International Date Line (IDL)?
The International Date Line (IDL) is an imaginary line on Earth's surface defining the boundary between one day and the next.
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The International Date Line (IDL) on the map.
The International Date Line is located halfway around the world from the prime meridian (0° longitude) or about 180° east (or west) of Greenwich, London, UK, the reference point of time zones. It is also known as the line of demarcation.
The Dateline Is Not Straight
The dateline runs from the North Pole to the South Pole and marks the divide between the Western and Eastern Hemisphere. It is not straight but zigzags to avoid political and country borders and to not cut some countries in half. On timeanddate.com's Time Zone Map, the IDL is shown as a black line (see image).
What Happens When You Cross the Dateline?
When you cross the International Date Line from west to east, you subtract a day, and if you cross the line from east to west, you add a day.
Depending on which time zone the country follows, the time difference on either side of the line is not always 24 hours. For example, if you travel the 1061 kilometers (659 miles) across the dateline from Baker Island to Tokelau you have to add 25 hours, or 1 day and 1 hour.
Three Dates at the Same Time
Every day between 10:00 and 11:59 UTC, three different dates on the calendar are in use at the same time on Earth. For example, our Time Zone Converter shows:
- At 10:30 UTC on May 2, it is
- 23:30 (11.30 pm) on May 1 in American Samoa (UTC−11),
- 06:30 (6:30 am) on May 2 in New York (UTC-4), and
- 00:30 (0:30 am) on May 3 in Kiritimati (UTC+14).
Changing Sides of the Dateline
The dateline is not defined by international law. Countries are free to choose the date and time zone that they want to observe.
For example, when the Republic of Kiribati gained independence from being a British colony in 1979 some of the islands were on one side of the dateline, and the rest were on the other. They corrected the anomaly in the eastern half of Kiribati by skipping January 1, 1995 and ever since Kiribati has been the first country to enter the New Year.
In 2011, Samoa changed the time zone from UTC-11 to UTC+13 by shifting the dateline to the west and removing December 30, 2011 from the calendar. They did this to facilitate trade with Australia and New Zealand, and Tokelau followed Samoa for the same reasons.
Drawn up in 1884
The 180° meridian was selected as the International Date Line because it mostly runs through the sparsely populated Central Pacific Ocean. It was decided at the International Meridian Conference in 1884 in Washington, D.C. where 26 countries attended.
Jet Lag
A state of exhaustion experienced by air travelers when they cross several time zones in a relatively short time as when one flies from India to U.S.A. The condition arises from disturbances in the body's habitual rhythms of 'internal clock' by suddenly requiring it to adapt to a strange new 24-hour time-scale. Time zones are imaginary lines that run from north to south on the map. These help standardize time throughout the world since it is only possible to cross them by travelling from east to west or visa versa, jet lag is, therefore, experienced only when long distances are travelled along the east-west axis. Jet lag generally includes a feeling of fatigue, hunger at unexpected times, irregular bowel and bladder movements. The only way to combat it is adequate rest at the end of the flight.
THE EARTH IN SPACE
Life did not come into being with the birth of the Earth. Scientists agree that the life of the Earth may range from 3 to 5 billion years. The Earth cooled from its gaseous state into liquid one. It later covered itself with a solid layer on further cooling. The formation of its atmosphere must have simultaneously taken place. Life began in the sea in the form of one cellular organism which belonged to both animal and vegetation kingdom. Later, the animals and vegetations both evolved into more complex life forms.
The age of the Earth.... 5,000,000,000 years (Approximately)
The dawn of life on Earth..... 500,000,000 years (Approximately)
Appearance of Man on Earth....500,000 years (Approximately)
Basic Planetary Data
The mean distance of the Earth from the Sun is approximately 1.5 X 108 kilometres. The planet orbits the Sun in a path that is presently more nearly a circle than are the orbits of most other planets. The direction of the Earth’s revolution—counterclockwise as viewed down from the north—is in the same sense (direction) as the rotation of the Sun; the Earth’s spin, or rotation about its axis, is also in the same “direction” sense i.e. west to east or anti-clockwise. The length of a day (23 hours, 56 minutes, and 4 seconds) is typical of other planetary objects; Jupiter and most asteroids have days less than half as long, while Mercury and Venus have days more nearly comparable with their orbital periods. The tilt (inclination) of the Earth’s axis to its orbit (23.5º), also typical, is responsible for the change of seasons.
Compared with the other eight planets of the solar system, the Earth is relatively small. Although it is the largest of the inner planets, it is considerably smaller than the gas giants of the outer solar system. The Earth has a single satellite, the Moon. The Moon is one of the bigger natural satellites in the solar system and is in fact relatively large compared with the Earth itself. Some people consider the Earth-Moon system a double planet, with some similarities to the Pluto-Charon system.
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Some Important Facts about the Earth
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1.
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Age
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5000 million years
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2.
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Total surface area
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51 x 107 km2
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3.
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Land area
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29.2% of the total surface area
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4.
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Water area
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70.8% of the total surface area
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5.
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Highest land point
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8848[1] metres (Mt. Everest)
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6.
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Lowest land point
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397 metres below sea level (Dead Sea in Jordan)
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7.
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Mean ocean depth
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3554 metres
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8.
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Mean land elevation
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3800 metres
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9.
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Average density
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5.5 gm/cm3
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10.
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Average temperature
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15oC
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11.
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Lowest ocean point
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11033 metres (Mariana Trench)
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12.
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Difference between polar & equatorial diameters
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43 Kms
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13.
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Difference between longitudinal &equatorial circumference
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69
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The Earth’s gravitational field is manifested as the attractive force acting upon a free body at rest, causing it to accelerate in the general direction of the centre of the planets. Departures from the spherical shape and the effect of planetary rotation cause gravity to vary with latitude over the terrestrial surface. The average gravitational field at sea level is about 9.80 m/s2, although values range from about 9.78 m/s2 at the Equator to about 9.83 m/s2 at the poles. So, the gravitational pull is essentially higher at poles than at equator due to proximity to the core.
Gravity typically is not measured at sea level. So corrections must be made for its decrease in value with increasing elevation. Such height-related gravity anomalies may be corrected for by using free-air or Bouguer reductions. In the Bouguer reduction, the effect of the attraction of the additional mass located above sea level is taken into account, while in the free-air reduction this mass effect is ignored. The Bouguer anomaly can be used to indicate variations of density within the Earth by measuring the corresponding variation in gravity.
The Earth’s gravity keeps the Moon in its orbit around the planet and also generates tides in the body of the Moon. Such deformations are manifested in the form of slight bulges at the lunar surface, detectable only by sensitive instruments. The Moon, owing to its relatively large mass, exerts a gravitational force that likewise causes tides on the Earth. These are most readily observable as the daily rises and falls of the ocean water, although tidal deformations occur in the solid Earth as well as in its atmosphere.
Continents