Stars and Solar System:
The planets:
The planets look like stars, but they do not have light of their own. They merely
reflect the sunlight that falls on them. A planet has a definite path in which it
revolves around the sun. This path is called an orbit. The time taken by a planet to
complete one revolution is called its period of revolution. The period of revolution increases as the distance of the planet from the sun increases.
Besides revolving around the sun, a planet also rotates on its own axis like a top. The time taken by a planet to complete one rotation is called its period of rotation.
Some planets are known to have moons/satellites revolving round them. Any
celestial body revolving around another celestial body is called its satellite.
The earth revolves around the sun. Does it make earth a satellite of the sun?
The earth and other seven celestial bodies can be said to be as satellite of the sun, though generally we call them as planets of the sun. We use the term satellite for the bodies revolving around planets. Moon is a satellite of the earth. There are many man-made satellites revolving round the earth. These are called artificial satellites.
Mercury (Budhudu)
The planet mercury is nearest to the sun. It is the smallest planet of our solar system.Because mercury is very close to the sun, it is very difficult to observe it, as most of the time it is hidden in the glare of the sun. However, it can be observed just before sunrise or just after sunset, near the horizon. So it is visible only at places where trees or buildings do not obstruct the view of the horizon. Mercury has no satellite of its own.
Venus (Sukrudu):
Venus is earth’s nearest planetary neighbour. It is the brightest planet in the night sky. Sometimes, Venus appears in the eastern sky before sunrise. Sometimes, it appears in the western sky just after sunset. Therefore, it is oftencalled a morning or an evening star, although it is not a star. Try to locate Venus in the night sky during early winter.Venus has no satellite of its own. Rotation of Venus on its axis is some what unusual. It rotates from east to west while the earth rotates from west to east.
The Earth (Bhoomi):
The earth is the only planet in the solar system on which life is known to exist. Some special e n v i r o n m e n t a l conditions are responsible for the existence and continuation of life on the earth. These include just the right distance from the sun so that it has the right temperature range, the presence of water and suitable atmosphere and a blanket of ozone. We must take special care to protect our environment so that life on earth is not disturbed. From space, the earth appears blue- green due to the reflection of light from water and landmass on its surface. The earth has only one moon revolving around it.
Mars (Kujudu / Angarakudu):
The first planet outside the orbit of the earth is mars. It appears slightly reddish and therefore, it is also called the red planet. Mars has two small natural satellites.
Mars science laboratory:National Aeronautic and Space Administration (NASA) in America started a mission called ‘Mars Science Laboratory’ on 26 th November 2011, to know more about Mars. A rover named ‘Curiosity’ landed on Mars on 6th August 2012. It is analyzing the elements in the rocks of the surface of the Mars. It found few indications of water on Mars. It is searching whether the favorable conditions for lifeexist on Mars.
Jupiter (Brihaspati):
Jupiter is the largest planet of the solar system. It is so large that about 1300 earths can be placed inside this giant planet. However, the mass of Jupiter is about 318 times that of our earth. It rotates very rapidly on its axis. Jupiter has a large number of satellites. It also has faint rings around, appears quite bright in the sky. If you observe it with the help of a telescope, you can also see four of its large moons.
Saturn (Shani):
Beyond Jupiter is Saturn which appears yellowish in colour. What makes it unique in the solar system is that it has rings. These rings are not visible to the naked eye. You can observe them
with a small telescope. Saturn also has a large number of satellites.
Uranus and Neptune:
These are the outermost planets of the solar system. They can be seen only with the help of large telescopes. Like Venus, Uranus also rotates from east to west. The most remarkable feature of Uranus is that it has highly tilted rotational axis . As a result, in its orbital motion it appears to roll on its side. The first four planets, mercury, venus, earth and mars are much nearer the sun than the other four planets. They are called the inner planets. The inner planets have very few moons. The planets outside the orbit of Mars, namely Jupiter, Saturn, Uranus and Neptune are much farther away from the sun than the inner planets. They have a ring system around them. The outer planets have a large number of moons.
Asteroids
There is a large gap in between the orbits of mars and Jupiter . This gap is occupied by a large number of small objects that revolve around the sun. These are called asteroids. Asteroids can only be seen through large telescopes.
Comets
Comets are also members of our solar system. They revolve around the sun in highly elliptical orbits. However, their period of revolution round the sun is usually very long. A comet appears generally as a bright head with a long tail.The length of the tail grows in size as it approaches the sun. The tail of a comet is always directed away from the sun ).
The diameter of the sun is 13,92,000 Km.
The diameter of the earth is 12,756Km.
The diameter of the moon is 3,474 Km.
The distance from the sun to earth is 15,00,00,000 Km.
The distance from the earth to moon is 3,84,399 Km.
Take the scale as 1 lakh km = 1 cm,
Do you know?
Till 25th August 2006 we used to say there are nine planets in our solar system.
The ninth planet at that time was ‘Pluto’. In the 26 th general assembly of International Astronomical Union it was decided that ‘Pluto’ is no more a planet.
The decision was taken since it was observed that Pluto does not follow the
rule of “cleared the neighborhood.” That means, sometimes it is entering into the
orbit of Neptune. Some other members of the solar system.
There are some other bodies which revolve around the sun. They are also members of the solar system. Let us know about some of them.
Many comets are known to appear periodically. One such comet is Halley’s comet, which appears after every 76 years. It was last seen in 1986. Can you tell when
Halley’s comet will be visible again?
Meteors and Meteorites
At night, when the sky is clear and the moon is not visible, you may sometimes see bright streaks of light in the sky .These are commonly known as shooting stars, although they are not stars.They are called meteors. A meteor is usually a small object that occasionally enters the earth’s atmosphere. It has a very high speed. The friction due to the atmosphere heats it up. It glows and evaporates quickly. That is why the bright steak lasts for a very short time. Some meteors are large and so they can reach the earth before they evaporate completely. The body that reaches the earth is called a meteorite out of the earth? To get clarity asume fencing around the flat earth.After that
1) They assumed the shape of earth as round by observing the shadow of earth in lunar eclipse. In every eclipse they found the shape of earth is in round even though there is a chance of getting linear, elliptical shadows by a circular object.
2) Some sailors, who started their journey in ocean, reached the same place after travelling large distance in one direction only.
3) Observing ships approaching the port also helped to change their opinion about the shape of the earth, that is, usually they see smoke of the ship first and then the top of the ship after that the whole ship.
4) Observations about the movement of stars and different stars visible from different places on the earth also helped to think about the shape of the earth. Through all such observations made by so many people at so many places on the earth they came to an understanding that earth is spherical. And then it is get clarified in 1969 when man landed on the moon and observed the earth’s shape from the moon.
How did people come to an understanding that earth rotates on its own axis? People from olden days thought that earth is located in the center of the universe with sun, moon and stars moving around it. They also thought that sun, moon and stars are
located on transparent concentric spheres sorrounding the earth, because they are not falling down. The three spheres are rotating on their axis from east to west that is why sun,moon and stars appear to revolve from east to west around the earth. They also assumed that the sphere on which sun is located rotates east to west and oscillates from south to north that is why uttarayanam and dakshinayanam are happening.
Because of the uneven movement of some stars (actually they are planets) which they observed, it became very difficult to explain the model of universe which required so many transparent spheres around the earth. Nicholas Copernicus
suggested that the sun is at the center of the universe and all other celestial objects
are revolving around the sun. Then how do day and nights occur. It was assumed that earth rotates on its axis. This model could explain the occurence of day and night.In this way people came to an understanding that earth rotates on its axis.