The Solar System
* The solar system is made up of the sun, the eight planets and the other bodies like satellites, asteroids, meteoroids and comets.
* Earth is a part of the solar system, which is a part of the Milky Wave galaxy (Akash Ganga).
* The sun exerts a force on all the other bodies that holds the solar system together.
* We do not feel its tremendous heat as it is 150 million kilometres away.
* All the eight planets move around the sun along fixed paths called their orbits.
* The paths along which the planets move around the sun are elliptical orbits.
* The eight planets of the solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
* Venus is very similar to Earth in size and shape; It is called the Earth’s twin.
* Earth is the third planet in the line from the sun. It takes about 365 days the complete one round along its orbit.
* Pluto is not considered to be a planet now.
* A new planet, 2003 UB313, Which is the farthest from the sun, has been discovered by scientists.
* Earth is a unique planet as it is probably the only planet that supports life. It is also called the blue planet.
* The earth is the third nearest planet to the sun; it is also the fifth largest planet.
* The earth is slightly flattened at the poles. Such as shape is given the name Geoid (earth – like shape).
* The diameter of the moon is only one – quarter that of the earth. The moon is about 3, 84,400 kilometres away from us.
* There are two movements that define the moon’s motion.
* The first movement of the moon is along its own axis.
* The second movement is around the earth along a fixed orbit.
* Conditions on the moon are not favourable for humans to survive there.
* The moon has many mountains, plains and depressions, which caste shadows and give an uneven appearance to the moon.
* Numerous tiny bodies called asteroids move around the sun. They are located between the orbits of Mars and Jupiter.
* The largest asteroid observed in the solar system is called Ceres.
* Small pieces of rocks called meteoroid also move around the sun.
The Globe
* The earth is flattened at the North and South Poles and is bulging at the centre.
* A globe is a miniature model of the earth.
* Countries, continents and oceans on a globe are shown to scale.
* A globe can be rotated.
* We need some points of reference to describe the location of a point on a sphere like the earth.
* The earth rotates on an imaginary axis. The earth’s axis is titled at the angle of 23½° to the vertical.
* The points through which the earth’s imaginary axis passes are the North Pole and the South Pole.
Latitudes
* Latitudes are angular measurements on the globe, ranging from zero to 90 degrees.
* The equator is 0° latitude.
* The equator divides the earth into the Northern Hemisphere and Southern Hemisphere.
* The North and south Poles are at 90° to the equator.
* Two places may have the same latitude, but they may be located north or south of the equator. Letters N and S are used to indicated whether a place is located in the Northern or the Southern Hemisphere.
* Important Parallels of Latitude are: Equator, Tropic of Cancer, Tropic of Capricorn, Arctic Circle, Antarctic Circle.
* Latitudes play an important role in determining the weather and climate of a region.
* Based on the latitudes, there are a number of climatic zones on the earth: The Torrid Zone, The Temperate Zones, and The Frigid Zones.
* It is relatively easier to determine the latitude at the particular place by using celestial bodies and their movements as reference points.
Longitudes
* The imaginary lines running from the North Pole to the South Pole on the globe are called longitudes
* Knowing the latitude and the longitude of a place, we can determine its location on the globe accurately.
* The grid pattern formed by plotting the lines of latitude and longitude on a map is called the Earth grid or Graticule.
* Distance between longitudes are measured in degrees of longitude’. Each degree is further divide into minutes, and minutes into seconds
* Longitudes are semi – circular in shape.
* The distance between longitudes decreases as they move towards the poles.
* Longitudes are of equal length.
* The 0° longitude passes through Greenwich and is called the Prime Meridian.
* The Prime Meridian divides the earth into the eastern hemisphere and the western hemisphere
* The longitude of a place is followed by the letter E or W. 180° East meridian and 180° West meridian are the same.
* If you cross the 180° longitude, the day and the date changes. It is, therefore, also known as the International Date Line.
* To avoid having two different dates in the same country, the International Date
* Line has been made to bend at several places.
* A great circle bisects the earth into two equal hemispheres. A great circle is the shortest distance between any two points on the globe.
* Basic difference between latitudes and longitudes:
Latitudes Longitude
* Horizontal lines that run west and east Vertical lines that run north to south
* Run parallel to the equator and the each other.
* Not parallel lines; do not run parallel to the Prime Meridian
* Measure the distance north or south of the equator
* Measure distance north or south of the equator
* Lines get shorter as towards the poles and finally
* Lines of equal length, converging on average at the poles
* Values range from 0° latitude to 90°N/ 90°S
* Values range from 0° longitude to 180°E/ 180°W
Longitudes and Time
* The time at any location in the world is calculated on the basis of the Prime Meridian.
* The local time at Greenwich is considered the accurate time for the Prime Meridian, and is called Greenwich Mean Time or GMT.
* All the places on a particular meridian or particular longitude have the some local time.
The earth rotates:
* 360° in 24 hours
* 15° in 1 hour
* 1° in four minutes
* Areas on the east of the Prime Meridian are ahead of areas on the West.
* Indian Standard Time is based on the time on longitude 82.5 degrees east that passes through Mirzapur.
* IST is 5 hours 30 minutes ahead of GMT.
* Countries like the USA and Russia have several standard time zone.
* Multiple time zones exist in these countries because they are spread across a large number of longitudes.
* The earth has a total of 24 time zone of one hour each.
Rotation
* Rotation is the earth’s motion as it spins around its own axis.
* The earth spins at an angle of 66½ degrees to its orbital plane.
* The earth takes 24 hours to complete one rotation around itself.
* The orbital plane is the plane formed by the earth’s orbit.
* Only half of the earth faces the sun at one time. This half experiences day, while the other half experiences night.
* Thus, night and day are caused because of the earth’s rotation.
Revolution
* The earth takes one year, or about 365 days, to revolve once around the sun.
* The earth rotates on its own axis
* The earth revolves around the sun in an elliptical orbit.
* A full revolution takes 365¼ days.
* A leap year comes every four years – the extra day in a leap year is formed by adding up the quarter days, or six hours, over four years.
* The earth’s axis is inclined at an angle of 23½ degrees to the vertical.
* The earths tilt and revolution cause the change of seasons.
* The northern hemisphere receives sunlight for the longest duration June 21.
* This position of the earth is called the Summer Solstice.
* In summer, the days are longer and the nights shorter.
* Daylight can last for up to six months in the Arctic region during the summer.
* The northern hemisphere receives sunlight for the shortest duration on December 22. This position of the earth is called the Winter Solstice.
* The equator receives direct sunlight on March 21 and September 23, resulting in day and night of equal durations. This phenomenon is known as an Equinox.