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00:00STARS, PLANETS AND THE UNIVERSE
00:07A student of standard 3 is playing in the garden at 8 pm on a summer evening.
00:17Her 12 year old brother Raghav is also playing with her.
00:25At night there are so many stars in the sky. There is not a single star in the sky at day time.
00:34Manju, you are wrong. There is a star in the sky at day time also.
00:42How is it possible? I have never seen any star at day time.
00:48It is big, bright and shiny. You just can't miss it.
00:55Oh, you mean the sun. But is the sun a star?
01:02Yes, the sun is a star.
01:07How can that be? The other stars look so small.
01:13That's because those stars are millions and millions of miles away.
01:20The sun is the nearest star to the earth.
01:25Is our earth also a star?
01:29No, it's a planet.
01:33Why is the sun called a star and the earth a planet?
01:39Every star is a huge ball of burning gases giving off heat and light.
01:47Planets are round ball shaped bodies but they do not have any light of their own.
01:57They shine in the reflected light of the sun.
02:04Why do the other stars disappear during the day?
02:08No, they do not disappear.
02:13They are there in the sky even during the day.
02:18We cannot see them because of the bright light of the sun.
02:24This is what we see when we look at the night sky.
02:31Raghav did tell about the stars glittering in the sky.
02:36But there are many more types of bodies besides stars and planets.
02:44The sky is also called heaven.
02:49The sky is also called heaven.
02:52And therefore all these bodies including the earth are called heavenly bodies or celestial bodies.
03:04The study of all natural objects or heavenly bodies in the universe is called astronomy.
03:14The scientists who study and conduct research in astronomy are called astronomers.
03:24An astronaut is a person who travels outside the earth's atmosphere into the outer space in a spaceship or spacecraft to find out more about space.
03:41Astronaut is an American word.
03:46In Russia, they are known as cosmonauts.
03:52A star is an unimaginably large sphere like a ball of hot burning gases that gives out heat and light.
04:07Our sun is a star.
04:12Some stars in the universe are much bigger than the sun.
04:19They appear as very small points of light in the sky because they are very far from the earth.
04:31If we were to fly in a jet plane moving at a speed of 1000 km per hour,
04:40it would take us 17 years of non-stop flight to reach the sun from the earth.
05:00A galaxy is a group of many stars.
05:07Our sun is a part of the Milky Way galaxy.
05:14Our galaxy is a spiral galaxy.
05:20Our galaxy looks like a band running across on a clear night sky.
05:28When seen from an open ground, the universe may contain 100 billion galaxies.
05:39CONSTELLATIONS
05:43When seen from the earth, there are certain groups of stars forming recognizable patterns or figures called constellations.
05:57If you look towards the north sky on a clear night,
06:02you can see seven stars making a pattern called the Big Dipper or Ursa Major, Latin Great Bear.
06:16This is also called the Saptarishi.
06:23The brightest star in the northern sky, the Polaris or Dhruvtara,
06:31is a part of the constellation Ursa Minor, Latin Little Bear.
06:39Some other constellations are Leo, Orion and Centaurus.
06:52THE SOLAR SYSTEM
06:55A solar system comprises planets, satellites, dwarf planets or planetoids, asteroids, comets and meteors.
07:11The Milky Way galaxy contains our solar system.
07:20The sun with all the heavenly bodies that revolve around it form the solar system.
07:32Eight planets namely Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune revolve around the sun.
07:52The sun, our closest star, is about 150 million kilometers away.
08:03PLANETS
08:05Planets are heavenly bodies that revolve around a star,
08:11for example, sun in their own particular path called the orbit.
08:19The orbit is elliptical or oval in shape.
08:25They do not have light of their own.
08:30We see them shining because they reflect the light of the star around which they revolve.
08:41Of the eight planets that revolve around the sun, Mercury is the closest to the sun.
08:50It is also the smallest planet of the solar system.
08:56Venus is the hottest planet as its atmosphere retains all the heat of the sun.
09:07Next is the planet Earth, which has water and an atmosphere which supports life.
09:17Mars, the red planet, lies forth from the sun.
09:24It gets its red color from the mineral ion that is present in abundance on its surface.
09:35Next four planets, Jupiter, Saturn, Uranus and Neptune comprise more of gaseous matter than solid rocks and are thus called the gas giants.
09:54Jupiter is the largest planet in the solar system.
10:02Saturn is the second largest planet after Jupiter and has rings around it that are composed of ice, rocks and dust.
10:16Some of the rings can be seen from the Earth through a telescope.
10:25Uranus and Neptune are much smaller than the other two gas giants.
10:33Uranus is the third largest planet.
10:38Approximately four times the size of the Earth, Neptune is the farthest from the sun.
10:50Beyond Neptune lie the planetoids or dwarf planets.
11:04Satellites are the heavenly bodies that revolve around specific planets and not around the sun independently.
11:18All the planets in the solar system, other than Mercury and Venus, have one or more satellites revolving around them.
11:31The Earth also has its own natural satellite, the Moon.
11:41Other heavenly bodies in the solar system, dwarf planets.
11:49In 2006, astronomers decided to place Pluto in a new category of objects because of its size.
12:04Beyond Neptune, Pluto and some others like Eris are small heavenly bodies that revolve around the sun.
12:18These are called dwarf planets or planetoids.
12:26Asteroids are tiny celestial bodies that revolve around the sun.
12:37They are smaller in size than the dwarf planets.
12:45These are found orbiting between Mars and Jupiter, forming what is called an asteroid belt.
13:01The small bodies made of frozen gases, rock and dust are called comets.
13:12When a comet passes close to the sun, the intense heat of the sun heats up the comet and gases are released.
13:25These gases form a tail that points in the direction away from the sun.
13:35The Halley's comet is visible from the Earth every 75 to 76 years.
13:45It was last observed in 1986.
13:56Meteors
13:58Sometimes we see a burning object falling from the sky.
14:05These are called meteors.
14:10They are smaller parts of asteroids and comets that enter the Earth's atmosphere and burn.
14:22They are known as shooting stars.
14:27Sometimes meteors do not burn up completely and are called meteorites.
14:37These meteorites strike the surface of the Earth, creating craters.