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Thursday, October 21, 2010

EARTH IS IN DANGER

OUR PLANET IS IN DANGER
1.Black Hole
2.Asteroids and Comets
3.Distortion in Planetary Motion 
4.Supernova 
5.Global Warming

1.Black Hole
        A black hole is a region of space from which nothing, not even light, can escape. It is the result of the deformation of spacetime caused by a very compact mass. Around a black hole there is an undetectable surface which marks the point of no return, called an event horizon. It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect black body in thermodynamics. Quantum mechanics predicts that black holes also emit radiation like a black body with a finite temperature. This temperature decreases with the mass of the black hole, making it unlikely to observe this radiation for black holes of stellar mass.

2.Asteroids and Comets
        Asteroids , sometimes grouped with Centaurs, Neptune trojans and trans-Neptunian objects into minor planets or planetoids, are a class of small Solar System bodies in orbit around the Sun. The term "asteroid" was historically applied to any astronomical object orbiting the Sun that was not observed to have the characteristics of an active comet or a planet, but it has increasingly come to particularly refer to the small rocky and metallic bodies of the inner Solar System and out to the orbit of Jupiter. As small objects in the outer Solar System have begun to be discovered their observed composition differs from the objects historically termed asteroids. Harbouring predominantly volatiles-based material similar to comets rather than the more familiar rocky or metallic asteroids, they are often distinguished from them.
        A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma (a thin, fuzzy, temporary atmosphere) and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei are themselves loose collections of ice, dust, and small rocky particles, ranging from a few hundred meters to tens of kilometers across. Comets have been observed since ancient times and have historically been considered bad omens.

3.Distortion in Planetary Motion 
         The planets rotate around invisible axes through their centres. A planet's rotation period is known as its day. Most of the planets in the Solar System rotate in the same direction as they orbit the Sun, which is counter-clockwise as seen from above the sun's north pole, the exceptions being Venus and Uranus which rotate clockwise, though Uranus's extreme axial tilt means there are differing conventions on which of its poles is "north", and therefore whether it is rotating clockwise or anti-clockwise. However regardless of which convention is used, Uranus has a retrograde rotation relative to its orbit.
4.Supernova

          A supernova (plural supernovae) is a stellar explosion that is more energetic than a nova. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. During this short interval a supernova can radiate as much energy as the Sun is expected to emit over its entire life span.The explosion expels much or all of a star's material at a velocity of up to 30,000 km/s (10% of the speed of light), driving a shock wave into the surrounding interstellar medium. This shock wave sweeps up an expanding shell of gas and dust called a supernova remnant.