THE SOLAR SYSTEM
A billion of stars and clouds of dust and gases that makes the GALAXY. There are million of such galaxies that make the UNIVERSE.
It is a cluster of millions of stars. Our solar system is a part of this galaxy. In ancient times it was also known as AKASH GANGA.
All those objects shining in the night sky are called celestial bodies.some of these bodies are very big and hot.They are made up of gases.They produce their energy by nuclear fusion at the core.Thus they have their own heat and light.Such celestial bodies are called stars.The sun is a star.
The various patterns formed by different groups of stars are called CONSTELLATIONS. Ursa major or big bear is one such constellation. One of the easily recognizable constellation is the SAPTARISHI. It is a group of seven stars that forms a part of Ursa major constellation.
In ancient times, people used to determine directions during the night with the help of stars. The North star indicates the north direction. It is also called the Pole Star. It always remains in the same position in the sky. We can locate the position of the Pole Star with the help of the Saptarishi.
The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system. We often call it a solar family, with the sun as its Head.
The sun is in the centre of the solar system. It is huge and made up of extremely hot gases. It provides the pulling force that binds the solar system. The sun is the ultimate source of heat and light for the solar system. In sun due to nuclear fusion large amount of hydrogen is converted into helium every second.Due to this process heat and light is creating.
- Some celestial bodies do not have their own heat and light. They are lit by the light of the stars. Such bodies are called planets.
- There are eight planets in our solar system. In order of their distance from the sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
- All the eight planets of the solar system move around the sun in fixed paths called Orbits.
- In our solar system except venus and Uranus all other planets are orbit the sun in the direction of the sun’s rotation which is anticlockwise direction. The rotatory motion of the planets (except venus and Uranus) is in the same direction as their revolution around the sun that is anticlockwise direction.
- These eight planets are further classified as innermost planets and outermost planets.
The inner four planets closest to the sun Mercury,Venus,Earth and Mars are often called the terrestrial planets because their surfaces are rocky.These planets are located in between of the sun and asteroid belt.
The outermost planets are Jupiter,Saturn,Uranus and Neptune are often called the gaseous planets.They are made up of gases and liquids.These are furthest planets from the sun.They are much bigger than rocky planets. They are the balls of hydrogen and helium.We cant stand on the surface of the planet because it is not solid.These planets are located in between of asteroid belt and kuiper belt.
Jupiter, Saturn and Uranus have rings around them. These are belts of small debris. These rings may be seen from the earth with the help of powerful telescopes.
Earth is the third planet from the sun. 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. The earth is neither too hot nor too cold. It has water and air, which are very essential for our survival. The air has life-supporting gases like oxygen. Because of these reasons, the earth is a unique planet in the solar system. From the outer space, the earth appears blue because its two-thirds surface is covered by water. It is, therefore, called a blue planet.
The moon is the only satellite of earth.The moon moves around the earth.It tooks 27 days to revolve around the earth.It takes exactly the same time to complete one spin.
Venus is considered as Earths twin because its size and shape are very much similar to that of the earth.
It is a celestial body that moves around the planets in the same way as the planets move around the sun. A Human-made Satellite is an artificial body. It is designed by scientists to gather information about the universe or for communication. It is carried by a rocket and placed in the orbit around the earth. Some of the Indian satellites in space are INSAT, IRS, EDUSAT, etc.
The International Astronomical Union(IAU) currently recognizes five drawft planets that are Ceres,Pluto,Haumea, Makemake and Eris.Here the Ceres is located at Asteroid belt.Except others are located at Kuiper belt.
Apart from the stars, planets and satellites, there are numerous tiny bodies which also move around the sun. These bodies are called asteroids. They are found between the orbits of Mars and Jupiter.
The small pieces of rocks which move around the sun are called meteoroids.Some times these meteoroids come near the earth and tend to drop upon it. During this process due to friction with the air they get heated up and burn. It causes a flash of light. Sometimes, a meteor without being completely burnt, falls on the earth and creates a hollow.
The miniature form of our earth is Globe. It is difficult to locate a point on a sphere like the Earth so there is a need of imaginary lines. Latitudes and Longitudes are the imaginary lines that are drawn on the Earth.
All parallel circles from the equator up to the poles are called parallels of latitudes. Its angle ranges from 0° at the Equator to 90° (North or South) at the poles. Lines of latitude, or parallels, run east–west as circles parallel to the equator. Latitudes are measured in degrees(°).
Equator is an imaginary circular line that divides the Globe into two equal parts. The northern half of the earth is called Northern hemisphere and the southern half of the earth is called southern hemisphere. They are the equal halves.
The equator represents the zero degree latitude(0°)
The north pole represents (90° N).
The south pole represents (90° S).
Latitudes never meet each other. If we move away from the equator the size of the parallels of latitude decreases.
The shortest points are North pole and south pole.
There are four important parallels of latitudes–
(i) Tropic of Cancer (23½° N) in the Northern Hemisphere.
(ii) Tropic of Capricorn (23½° S) in the Southern Hemisphere.
(iii) Arctic Circle at 66½° north of the equator.
(iv) Antarctic Circle at 66½° south of the equator.
EARTH’S HEAT ZONES:
Based on the heat zones of the earth, the zones are further classified into below three,
This zone is located inbetween of tropic of Cancer and the Tropic of Capricorn.
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.So that this zone receives maximum heat.
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.
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.
The area bounded by the Arctic Circle to the North Pole in the Northern Hemisphere and the Antarctic Circle to the South Pole in the Southern Hemisphere, are Frigid zones that is very cold. It is because here the sun does not rise much above the horizon. Therefore, its rays are always slanting and provide less heat.
The imaginary lines that drawn between north pole to the south pole are called longitudes.
Longitudes meet at poles.
Longitudes are equal in length.
The distance between the longitudes are measured in degrees of longitude.The meridian which passed through greenwich is called the prime meridian.Its value is 0° longitude.
If we count 180° eastward as well as 180° westward ,the prime meridian and 180° meridian divide the earth into two equal halves,the Eastern hemisphere and the Western hemisphere.
The time is measured by the movement of the earth, the moon and the planets. The sun regularly rises and sets every day, and naturally, it is the best time-keeper throughout the world.
When 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 is divided into 24 time zones of The earth rotates 360° in about 24 hours, which means 15° an hour or 1° in four minutes. Thus, when it is 12 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 12 noon at Greenwich.
INDIAN STANDARD TIME(IST):
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).
Indian Standard Meridian 82½° E.
ROTATION AND REVOLUTION:
The motions of earth is classified into below two that are,Rotation,Revolution.
It is the movement of the earth on its axis.Our earth rotates along its axis from west to east.It takes about 24 hours to complete one rotation around its axis.The period of rotation is known as the earthday.This is the daily motion of earth.
Due to the rotation of the earth Days and Nights occur.
The circle that divides the day from night on the globe is called the circle of illumination.
It is the movement of the earth around the sun in its orbit.It takes 365¼ days to revolve around the sun.If we consider a year as consisting of 365 days only and ignore six hours for the sake of convenience.The six hours saved every year are added to make one day (24 hours) over a span of four years.So this surplus day is added to the month of February. Thus every fourth year, February is of 29 days instead of 28 days. Such a year with 366 days is called a leap year.
Due to the revolution of earth around the sun seasons occur.
The position of the earth to the sun is divided into summer solstice and winter solstice.
On 21st March and September 23rd, direct rays of the sun fall on the equator.
At this position, neither of the poles is tilted towards the sun;
so, the whole earth experiences equal days and equal nights. This is called an equinox.
On 23rd September:
In northern hemisphere – Autumn season
In southern hemisphere – Spring season
On 21st March:
In northern hemisphere – Spring season
In southern hemisphere – Autumn season
ROTATION – DAYS AND NIGHTS
REVOLUTION – SEASONS CHANGE
Lithosphere is the solid portion of the earth.It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms.Lithosphere, rigid,rocky outer layer of the Earth, consisting of the crust and the solid outermost layer of the upper mantle. It extends to a depth of about 60 miles (100 km). The main two division of the earth’s surface are continents and ocean basins.The large landmasses are known as the continentsand the huge water bodies are called the ocean basins.
Continents are classified into below seven
- North America
- South America
- Asia is the largest continent. It covers about 30% of the total land area of the earth. This continent lies in the Eastern hemisphere.
- The Tropic of Cancer and Equator passes through this continent.
- There are 48 countries in Asia.
- It is bounded on the east by the Pacific Ocean, on the south by the Indian Ocean and on the north by the Arctic Ocean.
- Asia is separated from Europe by the Ural mountains on the west.
- The combined landmass of Europe and Asia is called the Eurasia (Europe + Asia).
- It is separated from Africa by the Red Sea and Suez Canal.
- It is separated from North America by Berling Strait.
- The important peninsulas in this continents are Arabian Peninsula, Indo-Chinese Peninsula and Deccan Peninsula.
- The Arabian Peninsula is the largest Peninsula in the World.
- Mariana Trench is the deepest trench in the world. It lies in the Pacific Ocean.
- The highest point and the lowest point on the earth are situated in this continent.
- Highest point – Mount Everest.
- Lowest point – Dead Sea.
- The highest annual rainfall in the World is received at Mawsynram near Cherapunji that is situated in the Khasi Hills in Meghalya.
Some of the biggest deserts in this continent are
- The Gobi desert – located at central Asia. (The Gobi desert stretches across huge portions of both Mongolia and China).
- The Takla Makan desert – located at western China.
- The Thar desert(Great Indian desert) – located at northwest of Indian subcontinent.
- The Kara-Kum desert – located at Turkmenistan.
- The Rub-al-Khali desert – located at Arabian peninsula(It covers Saudi Arabia, Oman, the United Arab Emirates, and Yemen).