Solar System
Satellite
A celestial body that revolves around a planet is called satellite. Satellites are known as moon also. There are two types of satellite – Natural satellites and Artificial satellites.
Natural satellites
Celestial bodies which revolves around a planet is called natural satellites. Our earth has only one natural satellite the moon. Some other planets of our solar system have more than one natural satellite. For example Saturan has 62 satellites and Jupiter has 67 satellites.
Artificial satellites
Man-made satellites sent to orbiting a planet are called Artificial Satellites. So, far thousands of aftificial satellites are launched which are revolving round the earth. There are many launched to orbit other planets too.
Artificial satellites are launched to make communication faster, better and easy. Such satellites are used in communication of telephone, television and radio signals. Artificial satellites are also used for weather forecasting.
Sputnik – was the first man made satellite launched by USSR (Union of Soviet Socialist Republic) on 4th October 1957. Aryabhatt was the first satellite sent to orbiting earth by India in the year of 1975.
Moon
Moon is the natural satellite of our planet earth. Since, moon revolves around the earth so it is a natural satellite of the earth. There is no water or air on the Moon. Moon is made of rocks. There are craters, mountains, and valleys on the surface of moon similar to earth. Since, moon is a planet, thus, it does not have its own light. We see moon as the brightest natural object in the night sky because it reflects a part of sunlight it receives from the sun. Sometimes we see moon in day time also. We do not see moon always in day time because of intense light of sun shine. Moon is the second brightest celestial object after sun.
Moon is known as Luna also.
Revolution of Moon
Moon completes one revolution round the earth in about 27 days. But due to movement of sun and moon both, we find successive new moon in every 29.5 days.
Moon is at a distance about 3,84,000 km from earth.
Moon: Gravity
Gravity is a force because of that a planet pulls an object towards it as a magnet pulls an object made of iron towards it.
Similar to other planet, moon also has gravity. This means moon also pulls an object towards it. But gravity on moon is 1/6 times of the gravity of earth. In other words, if the weight of an object is 6 kg on earth, it will be felt only 1 (One) kg on the surface of moon. You can easily carry a load on moon which is appears 60 kg on earth.
Phases of the moon
Shape of moon does not appear same every night rather we see different shapes of moon in night sky. This happens because changing position of moon and sun relative to earth. During change in position of moon only some of the portion of moon is illuminated by sun and we observe only that illuminated portion which resulting in different shapes of moon. This is called phases of moon.
Visibility of moon in different shapes from earth due to changing position of moon and sun relative to earth is called phases of moon.
Division of phases of moon
The phases of moon divided into two phases – Completely dark phase and a complete bright phage. Each of the phases is of about 15 days.
Completely dark phase of moon is called Amavas or New moon also. While a complete bright phase of moon is called Poornima or Full Moon also.
These phases are separated by nearly 15 days.
Moon: Some Important Facts
Size: The diameter of moon is 3475 km and radius of moon is equal to 1734 km
Atmosphere: Moon has no atmosphere.
Phases of moon: Moon has two phases – dark phases and bright phases. Complete dark phase is called new moon and complete bright phase is called full moon.
Mission: Luna 2 was the first successful space craft to touch the surface of moon in September 1959. Luna 2 was launched by Soviet Union.
Apollo 11 was the first space craft of USA which carried human to the surface of moon. Neil Armstrong and Buzz Aldrin landed on moon on 20th July 1969. Neil Armstrong was the first astronaut landed his feet on moon.
Eclipses
We know that earth revolves around sun and the moon revolve around the earth. Sometimes the sun, the earth and the moon come in a straight line, which is the cause of an eclipse, and the phenomena of eclipse takes place.
Eclipses are of two types - Solar eclipse and lunar eclipse.
Solar Eclipse
When the moon comes between the earth and sun; moon casts its shadow on earth. And the sun is not seen from the earth because of shadow of moon for some duration. This is called solar eclipse.
Lunar Eclipse
When the Earth comes between the sun and the moon, earth casts its shadow on moon and the moon is not seen from the earth. This is called the lunar eclipse.
In a calendar year there can be maximum seven eclipses taken place. Out of seven either two solar eclipses and five lunar eclipses or two lunar eclipses and five solar eclipses happen.