Topic:Universe
- 2. GALAXY A galaxy is a system of millions or billions of stars along with gas and dust, held together by gravitational attraction. On the basis of shape, galaxies are classified as: Irregular galaxy Spiral galaxy Elliptical galaxy Our solar system belongs to a spiral galaxy called the “Milky Way”
- 6. SOLAR SYSTEM •The solar system consists of the sun at the centre and the heavenly bodies that revolve around the sun in fixed paths called orbits. •These heavenly bodies include planets, the moons of the planets, dwarf planets and other solar system bodies such as asteroids, comets and meteoroids
- 7. SUN The Sun is a medium sized star, a very fiery spinning ball of hot gases. Three quarters of the Sun has hydrogen gas and one quarter has helium gas. It is over a million times as big as the Earth. Hydrogen atoms combine or fuse together to form helium under enormous pressure. This process, called nuclear fusion releases enormous amount of energy as light and heat. It is this energy which makes Sun shine and provide heat. Sun is situated at the centre of the solar system. The strong gravitational fields cause other solar matter, mainly planets, asteroids, comets, meteoroids and other debris, to orbit around it. Sun is believed to be more than 4.6 billion years old.
- 8. MERCURY Mercury is a rocky planet nearest to the sun. It is very hot during day but very cold at night. Its surface is covered with big holes called craters. Mercury can be seen as a bright spot of light in the sky before sunrise and just after sunset. It is the smallest planet of our solar system and has no moon
- 9. VENUS Venus is a special planet from the Sun, almost the same size as the Earth. It is the hottest planet in our solar system. After our moon, it is the brightest heavenly body in our night sky. This planet spins in the opposite direction to all other planets. So, unlike Earth, the Sun rises in the west and sets in the east here. Venus can be seen clearly through naked eye before sunrise and after sunset. Hence, it is also known as morning star or evening star. It always appears in the horizon of eastern or western sky and has no moon.
- 10. EARTH Earth is the third planet from the sun. The Earth where we live is the only planet in the solar system which supports life. Due to its right distance from the Sun it has the right temperature, the presence of water and suitable atmosphere and a blanket of ozone. All these have made continuation of life possible on the Earth. It has only one natural satellite, the moon. The earth takes 365.25 days to complete one revolution around the sun, which is one earth year. It takes about 24 hrs to rotate about its own axis
- 11. MARS 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 a very thin atmosphere and is cold It has two small natural satellites (Deimos and Phobos).
- 12. JUPITER Jupiter is called as Giant planet. It is the largest of all planets (about 11 times larger and 318 times heavier than Earth). It has 3 rings and 65 moons. Its moon Ganymede is the largest moon of our solar system.
- 13. SATURN Known for its bright shiny rings, Saturn appears yellowish in color. It is the second biggest and a giant gas planet in the outer solar system. At least 60 moons are present - the largest being Titan. Titan is the only moon in the solar system with clouds. Having least density of all (30 times less than Earth), this planet is so light.
- 14. URANUS Uranus is a cold gas giant planet and it can be seen only with the help of large telescope. It has a greatly tilted axis of rotation. As a result, in its orbital motion it appears to roll on its side. Due to its peculiar tilt, it has the longest summers and winters each lasting 42 years. It has more than 25 moons.
- 15. NEPTUNE It appears as Greenish star. It is the eighth planet from the Sun and is the windiest planet. It has 13 moons – Triton being the largest. Triton is the only moon in the solar system that moves in the opposite direction to the direction in which its planet spins.
- 16. DWARF PLANETS In the view of recent discoveries and our changing understanding of planetary systems, the IAU has placed Pluto, after seven decades, into another class of planets called “dwarf planets”. Since the highly elliptical orbit of Pluto lies in the same zone or overlaps with that of Neptune, it is classified as a dwarf planet. Ceres, Pluto and Eris are the first three heavenly bodies recognized as dwarf planets by the IAU.
- 17. PLUTO
- 18. CERES
- 19. ERIS
- 21. ASTEROIDS Asteroids means star-like. There is a large gap in between the orbits of Mars and Jupiter. This gap is occupied by a broad belt containing about half a million pieces of rocks that were left over when the planets were formed and now revolve around the Sun. These are called asteroids. The biggest asteroid is Ceres – 946 km across. Every 50 million years, the Earth is hit by an asteroid nearing 10 km across. Asteroids can only be seen through large telescope.
- 22. COMETS Comets are lumps of dust and ice that revolve around the Sun in highly elliptical orbits. Their period of revolution is very long. When approaching the Sun, a comet vaporizes and forms a head and tail. Some of the biggest comets ever seen had tails 160 million (16 crores) km long. This is more than the distance between the Earth and the Sun. Many comets are known to appear periodically. One such comet is Halley’s Comet, which appears after nearly every 76 years. It was last seen in 1986. It will next be seen in 2062.
- 23. METEORS AND METEORITES Meteors are small piece of rocks scattered throughout the solar system. Traveling with high speed, these small pieces come closer to the Earth’s atmosphere and are attracted by the gravitational force of Earth. Most of them are burnt up by the heat generated due to friction in the Earth’s atmosphere. They are called meteors. Some of the bigger meteors may not be burnt completely and they fall on the surface of Earth. These are called meteorites.
- 24. SATELLITES A body moving in an orbit around a planet is called satellite. In order to distinguish them from the man made satellites (called as artificial satellites), they are called as natural satellites or moons. Satellite of the Earth is called Moon (other satellites are written as moon). We can see the Earth’s satellite Moon, because it reflects the light of the Sun. Satellite moves around the planets due to gravity, and the centripetal force. Among the planets in the solar system all the planets have moons except Mercury and Venus.
- 26. WEATHER SATELLITES Weather satellites help to:- Monitor and forecast weather and climate of the earth Measure radiation released from the Earth’s surface and atmosphere Measure the temperature of the sea Monitor the amount of snow, movement of ice fields and depth of the ocean Detect forest fires and volcanic eruptions
- 27. COMMUNICATION SATELLITES Communication satellites pick up signals from one place on the earth and send them to other place on the earth. Some uses of these satellites are as follows. They pass on all kinds of communication signals such as radio, television, telephone transmissions and the internet. They help the military to collect and communicate information regarding battle zones, launch of missiles, etc.
- 28. NAVIGATION SATELLITES Navigation satellites provide geographical location of objects on the earth’s surface. A system comprising such satellites is termed as Global Navigation Satellite System(GNSS).Global Positioning System(GPS) is such a type of system. It has a variety of applications and is utilized across the globe. Some applications of GPS are as follows:- Location-based services such as finding the nearest hospitals or shops Land, sea and air navigation Emergency calls: GPS-based emergency system helps in identifying the source of emergency calls with accuracy. This would aid in rescuing people as fast as possible