The birth of the planets

   The nine planets, including earth , that form our solar system are accompanied through space by 63 moons, dozens of comets, and hundreds of thousands of lumps of rock that never grew into planets. all of them are held together and guided on their jorneys by the sun, which weighs almost 1000 times as much as the rest of the solar system put together.

WHERE DID THE PLANETS COME FROM?
    five or six billion years ago,  a disc-shaped cloud of dust and gas in our milky way galxy bagan to collapse inwards towards the centre-forming the sun. one theory suggests that specks of dust in the gas cloud around the sun kept bumping and clumping into each other until they formed the planets. another theory claims that the gas cloud broken up into large blobs, which got smaller and harder, forming the planets.


SCIENCE FACT OR FICTION?
   mars has often been thought to be inhabited by alien beings. in 1894 the america amateur astronomer percival lowell mapped  networks of 500 'canals', joined by 'oases', over the surface of the planets. he thought that they must have been dug by martians to water their dry and dusty landscape.
    from the close observation of the space probe viking 1 in 1976, we know that there are 'canal like' structures on the surface of mars, like the huge 4500 km (2800 miles) long 'mariner valley'. we also know that these 'canals' formed  naturally (like our own river valleys).the  'oases' are in fact huge volcanoes. one, called olympus mons, is the largest yet discovered in the solar system at 25km (15miles) high.

IS THERE LIFE ON OTHER PLANETS?
    scientists reckon that the chances of life somewhere else in the universe are high enough to spend hundreds of millions of dollars searching for it, but they are more doubtful about extraterrestrial life in our own solar system. life depends on two-dozen chemical elements,of which carbon,hydrogen, oxygen , nitrogen , sulphur and phosphorus are the most important. for life to continue, light and warmth are needed. mars has the right chemical ingredients and may once have had the right conditions. A 4.5 billion -years-old meteorite from mars , found in antarctica, contains what some scientists think is a fossilied microbe that may have lived on the 'Red Planet'.
      Conditions now, including subzero temperatures, are not suitable for life on mars. they may, however, be kinder on Europa, one of Jupiter's moons. Satellites have photographed ancient river valleys on Europa, and there may still be water below its ice cover.

HOW WAS THE EARTH FORMED?

     Scientists believed that the earth formed from dust particles that clumped together to form lumps, which collided and larger lumps and clusters, gradually building into a planet. Temperatures rose to more than 5000 C (9000 F)- enough to melt the early earth into a churning cauldron. a rocky crust. but deep inside the earth, temperatures are still 4500C (8100F) and the rocks are molten-rising to the surface most spectacularly when a volcano erupts.

that's amazing!!!

      BLACK HOLES

   massive stars, ten to a hundred times bigger than our Sun,have a life story different from the one illustrated here.
   they eventually explode,creating a supernova. all the matter from which they are made may collapse back on itself under gravity.not even light can escape from the collapsing star.it becomes a 'black hole' invisible to even the most powerful telescope. 









WHY IS THE SUN YELLOW?
 
       the colour of a star depends on how hot it is- and this, in turn , depends on its size and age. our sun is a star of medium size and brightness, with a surface temperature of about 5500 C (10000 F), which makes it look yellow. as it gets older and uses up more of its energy, the surface temperature will drop to about 4000 C (7200 F) and it will look red. when it has exhausted almost all of its energy, the sun will collapse and heat up briefly in a white flare.



WHAT MAKES THE SUN SHINE?

       light from the sun radiates through the entire solar system. this light is generated in the core of the sun, where temperatures reach around 15 million C (27 million F), as hydrogen gas is converted into another gas , called helium, in a series of thermonuclear explosions, billions of times more powerful than the biggest nuclear bombs: a mere  pinhead of these gases would be hot enough to ignite everything for 100 km (60 miles) around. the hot gases churn slowly towards the sun's surface, where the burning solar gas shines for millions of miles into space.


WILL THE SUN LAST FOREVER??

    stars last a long time, but not forever. our sun probably reached its peak brightness about 800 million years ago,and should continue to glow with the same intensity for another 1.5 billion years before beginning to fade. its decline will be a slow process. firts, in about 4 billion years, it will grow into a huge red giant star, swallowing the earth and the inner planets. then it will collapse into a white dwarf star before cooling and becoming extinct.

WHY DOES THE SKY CHANGE COLOUR?

Light rays from the sun are made up of violet,inaigo,blue,green,yellow,orange and red rays. When these rays pass though he atmosphere, they are scattered in a different directions.During daytimes, water droplets and gas molecules scatter blue light rays, making the sky look blue. In the evening ,the atmosphere can be full of dust particles.these scatter the red light rays,creating red sunsets.

selamat datang ke blog saya

Oceans and seas

     Oceans cover almost three quarters of the earth. Near coast they are often quite shallow, but in some places they can be over 10km (6miles) deep-more than enough to submerge a mountain the height of Mount Everest. If you threw a coin into water this deep, it would take more than an hour to reach the bottom . The surface and the seabed teem with life, but in between is an emptier world.

 
  why is seawater salty?

=If you have ever swallowed seawater while
swimming , you'll know that it is too salty to drink.This salt comes from rocks in the Earth's crust that have been dissolved by rain seeping throughbthe ground. Most of the salt is the kind we use on our food. If all the seawater evaporated and the salt was left behind, it would form a layer 55m (180 ft)deep.


  if we could walk on the seabed, what would it be like?
=in many places you would disappear,because you would sink into a deep layer of soft and slimy ooze.this ooze forms from the skeletons of tiny plants and animals that drift down  to the seabed after they die. the ooze forms at an amazingly slow rate- just a few millimetres a century-but it has been building up for so long that in some places it is several metres deep.