In this article, we will read about our planet earth. we will also learn about latitude and longitude, Motion of the Earth, Standard Time and Time zones, The International Date Line, Solar Eclipse, and Lunar Eclipse.
If You are new on this website and UPSC aspirant so, first of all, you should read the previous articles of Physical Geography.
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- Earth is the only known planet where life exists.
- Its surface area is covered with two-third of water that is why we call it a blue planet.
- Earth is the third planet from the sun, the densest planet in the solar system, the largest of the solar system’s four terrestrial planets.
- In size, it is the fifth-largest planet.
- It is slightly flattened at the poles, that is why its shape is described as a Geoid. Geoid means an earth-like shape.
Size and Shape of the Earth
- The shape of the Earth is called “geoid”
- The geoid bulges at the North Pole and is depressed at the South Pole.
Motions of the Earth
The Earth is constantly in motion, revolving around the Sun and rotating on its axis. These motions account for many of the phenomena we see as normal occurrences: night and day, changing of the seasons, and different climates in different regions.
The Earth spins on its axis from West to East (counter-clockwise). It takes the Earth 23 hours, 56 minutes, and 4.09 seconds to complete one full turn. Day and night are produced by the rotation of the Earth. The speed of rotation at any point upon the equator is at the rate of approximately 1,038 miles per hour, decreasing to zero at the poles.
While the Earth is spinning on its axis, it is revolving around the Sun in a counter-clockwise direction. It takes the Earth one full year to complete one full revolution around the Sun. This path is known as the Earth’s orbit. The mean distance of the Earth from the Sun is about 93 milling miles and the distance varies by 3 million miles, forming a slightly oval path.
The revolution of the Earth around the Sun traverses a distance of 595 million miles in 365 days, 6 hours, 9 minutes, and 9.5 seconds. This means a speed of 18 miles a second (or 66,000 miles per hour) while at the same time rotating once each twenty-four hours.
- Six hours saved every year are added to make one day (24 hours) over four years
- This surplus day is added to the month of February
- Thus, every fourth year, February is of 29 days instead of 28 days, and such a year with 366 days is known as a Leap Year.
Earth rotates in an elliptical orbit around the Sun
The orbit of the Earth around the sun is elliptical and not circular. Due to this, the distance between the Earth and the sun keeps changing.
When this distance is minimum, the Earth is said to be in perihelion (around January 3), When the distance is the maximum, it is said to be in aphelion (around July 4).
The Earth’s axis points constantly to the same point (the polar star) in the celestial sphere. As a consequence, the latitude on the surface of the earth at which the sun’s rays fall vertically keeps changing as the earth moves its orbit around the sun. Due to this, the earth attains four critical positions with reference to the sun.
- The equinoxes: On 21st March, the Earth has so positioned regarding the sun that the sun’s rays are vertical at the equator and the entire world experiences equal day and night.
- The autumnal equinox: A similar situation occurs on September 23.
- Summer solstice: On the 21st of June the sun’s rays are vertical over the Tropic of Cancer as the north pole of the Earth is inclined at its maximum towards the sun. At this time, the north pole experiences a long continuous day, and the south pole a long continuous night. The northern hemisphere has the summer season at this time and the southern hemisphere experiences winter now. Also, the days are longer than the nights in the northern hemisphere at this time.
- Winter solstice: On December 22, the position of the earth concerning the sun is such that the south pole is inclined at its maximum towards the sun and the Tropic of Cancer receives the vertical rays of the sun. This position is called the winter solstice when the sun shines continuously in the south polar region and it is a long continuous night at the north pole.
- This is the winter season in the northern hemisphere and the summer in the southern hemisphere. During the winter solstice, the days are longer than the nights in the southern hemisphere.
- Thus, the variation in the duration of day and night and the change of seasons is due to the earth’s revolution and the inclination of the axis of the earth. Also, the seasons are reversed from the northern to the southern hemisphere.
Latitudes and Longitudes
Latitudes and Longitudes are imaginary lines used to determine the location of a place on earth.
- Latitude is the angular distance of a point on the earth’s surface, measured in degrees from the center of the earth.
- Lines of Latitude run horizontally
- The Equator is 0 degrees Latitude.
- Lines of Latitude locate places North or South of the Equator.
- The North Pole is 90 degrees N Latitude, and the South Pole is 90 degrees S Latitude.
- There are 180 parallels of latitude. Their lengths are not equal and become smaller towards the pole.
- The distance between any two parallels of latitude is always equal.
IMPORTANT PARALLELS OF LATITUDES
Besides the equator (0°), the north pole (90°N) and the south pole (90° S), there are four important parallels of latitudes–
- Tropic of Cancer (23½° N) in the northern hemisphere.
- Tropic of Capricorn (23½° S) in the southern hemisphere.
- An Arctic circle at 66½° north of the equator.
- An antarctic circle at 66½° south of the equator.
Heat zones of the earth
- The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat and is called the torrid zone.
- The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. As such, the areas bounded by the Tropic of Cancer and the Arctic circle in the northern hemisphere, and the Tropic of Capricorn and the Antarctic circle in the southern hemisphere, have moderate temperatures. These are, therefore, called temperate zones.
- Areas lying between the Arctic circle and the north pole in the northern hemisphere and the Antarctic circle and the south pole in the southern hemisphere, are very cold. It is because here the sun does not rise much above the horizon. Therefore, its rays are always slanting. These are, therefore, called frigid zones.
- Lines of Longitude run vertically.
- They are also called Meridians.
- The Prime Meridian is found in Greenwich, England.
- The Prime Meridian is 0 degrees Longitude.
- Lines of Longitude locate places East or West of the Prime Meridian.
- There are 180 degrees of east Longitude, and 180 degrees of West Longitude.
- All Meridians are of equal length but they are not parallel and neither the distance between two meridians equal.
The units of measurement are angular and are shown in Degrees, Minutes, Seconds
- A Circle = 360 Degrees
- 1 Degree = 60 Minutes
- 1 Minute = 60 Seconds
Prime Meridian: The prime meridian (0°) splits the earth into the western hemisphere and eastern hemisphere.
Longitude and Time
The Prime Meridian of Greenwich has the sun at the highest point in the sky, all the places along this meridian will have mid-day or noon.
As the earth rotates from west to east, those places east of Greenwich will be ahead of Greenwich time and those to the west will be behind it
The earth makes one complete rotation of 360° in one day or 24 hours, it passes through 15° in one hour or 1° in 4 minutes.
Thus, when it is noon at Greenwich, the time at 15° east of Greenwich will be 15 × 4 = 60 minutes, i.e., 1 hour ahead of Greenwich time, which means 1 p.m. But at 15° west of Greenwich, the time will be behind Greenwich time by one hour, i.e., it will be 11.00 a.m. Similarly, at 180°, it will be midnight when it is noon at Greenwich.
At any place, a watch can be adjusted to read at 12 o’clock when the sun is at the highest point in the sky, i.e., when it is mid-day. The time shown by such a watch will give the local time for that place. You can see that all the places on a given meridian of longitude have the same local time.
Standard Time and Time zones
- The local time of places which are on different meridians is bound to differ. For example, it will be difficult to prepare a time-table for trains which cross several longitudes. In India, for instance, there will be a difference of about 1 hour and 45 minutes in the local times of Dwarka in Gujarat and Dibrugarh in Assam.
- It is, therefore, necessary to adopt the local time of some central meridian of a country as the standard time for the country. In India, the longitude of 82½° E (82° 30′ E) is treated as the standard meridian. The local time at this meridian is taken as the standard time for the whole country. It is known as the Indian Standard Time (IST).
- Earth Divided into twenty-four time zones of one hour each and Each zone Covers 15° of longitude.
- The larger country like the USA, Canada, and U.S.S.R. which have a great east-west stretch, it would be difficult to follow a single time zone, therefore, these countries have to adopt several time zones for a practical purpose.
- USSR the largest country (with east-west 165° extends) is divided into 11 time zones.
The International Date Line
- A traveler going eastwards gains time from Greenwich until he reaches the meridian 180°E when he will be 12 hours ahead of G.M.T.
- Similarly, in going westwards, he loses 12 hours when he reaches 180°W. There is thus a total difference of 24 hours or a whole day between the two sides of the 180° meridian.
- This is the International Date Line where the date changes by exactly one day when it is crossed. A traveler crossing the dateline from east to west loses a day (because of the loss in time he has made), and while crossing the dateline from west to east he gains a day (because of the gain in time he encountered).
When the light of the Sun or the Moon is blocked by another body, the sun or Moon is said to be in eclipse. The Sun, Earth, and Moon are in a straight–line Eclipses of the Sun is a solar eclipse and the Moon is a lunar eclipse.
It is caused when the moon Revolving around the Earth comes in between the Earth and the Sun, thus making a part or whole of the sun invisible from a particular part of the Earth thus, the eclipse can be partial or complete. It occurs during the day.
Type of Solar Eclipses
Total Eclipse: This occurs when the Sun is completely obscured from the rich. Instead, the Sun’s intense light is replaced by the dark silhouette of the Moon that is outlined by the Sun’s corona (the super-heated plasma extending out from the Sun.
Annular Eclipse: Occurs when the Sun and Moon are exactly in line but Moon appears smaller than the Sun. During one annular eclipse, the Sun appears as a bright ring around the Moon.
Partial Eclipse: Occurs when the Sun and Moon are not completely aligned and the Sun is partially obscured.
Hybrid Eclipse: Hybrid Eclipse is a combination of total and annular eclipse that takes place when a total eclipse changes to an annular eclipse or vice-versa along different sections of the eclipse’s path.
When the Earth comes between the Moon and the Sun, the shadow cast by the Earth on the Moon results in a lunar eclipse. It occurred at night.