The Earth, Rotation, Revolution, Equinoxes, Solstice, Latitude, Longitude, International Date Line and Eclipses

The Earth

* Also called 'Blue Planet'. It is the densest of all planets.

* Circumference : 40,232 Km, Area: 510 million sq km
* Two types of movement
 1. Rotation or daily movement
 2. Revolution or annual movement


* Spins on its imaginary axis from west to east in 23 hrs, 56 minutes and 40.91 seconds.

* Earth's rotation results in
(i) causation of days and nights.
(ii) change in the direction of wind and ocean currents.
(iii) rise and fall of tides everyday.
* The longest day in North Hemisphere is June 21,while shortest day is on 22 December (Vice-Versa in South Hemisphere).
*Days and nights are almost equal at the equator.


* It is earth's motion in elliptical orbit around the sun. Earth's average orbital velocity is 29.79 km/sec

* Takes 365 days, 5 hrs, 48 minutes and 45.51 seconds. It results in one extra day every fourth year.
* Revolution of the earth results in
(i) change of seasons.
(ii) Variation in the lengths of days and nights at different times of the year.
(iii) shifting of wind belts.
(iv) determination of latitudes.


* These are dates when days and nughts are equal. During these days the sun shines directly over the equator.

* March 21 Vernal equinox.
* September 23 Autumnal equinox.


* The time of the year when the difference between the length of days and the length of nights is the largest.

* During these days the sun shines directly over the tropics.
* June 21 Summer Solstice.
* December 22 Winter Solstice.


* Imaginary lines drawn parallel to the equator. Measured as an angle whose apex is at the centre of the earth.
* The equator represents 0° latitude, while the North Pole is 90°N and the South Pole 90°S.
* 23 1/2° N represents Tropic of Cancer while 23 1/2° S represents Tropic of Capricorn.


* It is the angular distance measured from the centre of the earth. On the globe the lines of longitude are drawn as a series of semicircle that extend from the North Pole to the South Pole through the equator. They are also called meridians.

* India, whose longitudinal extent is approx 30°, has adopted only one time zone, selecting the 82.5° East for the standard time which is 5 hours and 30 minutes ahead of GMT (Greenwich Mean Time).

International Date Line

* It is the 180° meridian running over the Pacific Ocean, deviating at Aleutian Islands, Fiji, Samoa and Gilbert Islands.
* Travellers crossing the Date Line from west to east (i.e. from Japan to USA) repeat a day and travellers crossing it from east to west ( i.e. from USA to Japan) lose a day.


Lunar Eclipse

* When earth comes between sun and moon.

* Occurs only on a full moon day. However, it does not occur on every full moon day.

Solar Eclipse

* When moon comes between sun and earth.

* Can be partial or total.
* Occurs only on new moon day when the moon is in line with the sun. However, due to the inclination of the moon's orbit, a solar ecliose doesn't occur on every new moon day.

Statistical Data of the Earth
Age4550 million years
Mass5.976x10^24 Kg
Volume1.083x10^24 m^3
Mean Density5.518 kg/lt
Total Surface Area510 million Sq KM
Land Area29.2% of the total surface area
Water Area70.8% of the total surface area
Rotation Speed23 hr, 56 min and 4.1 sec
Revolution Speed365 days, 5 hr and 45.51 sec
Dates when days and nights are equalMarch 21 (Vernal Equinox); 23 September, (Autumnal Equinox)
Longest day21 st June, (Summer Solstice) Sun is vertically overhead at Tropic of Cancer
Shortest night22 nd December, (Winter Solstice) Sun is vertically overhead at Tropic of Capricorn
Escape Velocity11.2 Km/sec
Mean Surface temperature14°C


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