Milky Way
The galaxy of which our star, the sun is a part is called the Milky Way. The Milky Way is a giant spiral galaxy measuring about 1.5 lakh light years across and 1500 light years thin (1 light year= 10 lakh crore km). Thus a flash of light traveling at its natural speed of 110 crore km per hour would take I lakh years to go from one side of the galaxy to the other. The Milky Way contains at least 1 lakh million, i.e., 10,000 crore stars located at huge distances from one another. Our solar system lies in one of the spiritual arms, about 33,000 light years from the centre of the galaxy. The sun traveling at a speed of 250 kilometers per second takes about 225 million years to complete one revolution around the Milky Way.
Moon
A natural satellite is orbiting a planet, and the name given to the earth’s natural satellite. Earth has one moon, mercury and Venus have no moons and Jupiter has the largest number of moons 62 discovered so far. The largest moon is in the solar system in Jupiter’s moon Ganymede. The second largest is Saturn’s moon Titan.
Stars are balls of gases mainly hydrogen and helium gas. There are trillions of them in the universe. Nuclear reactions in the heart of stars, like those in atom bombs, generate heat and light. In the core of star, hydrogen nuclei fuse to from atom. Astronomers work out how big a star is from its brightness and its temperature. The size and brightness of a star depends on its mass- that is, how much gas it is made of. Ur sun is a medium-sized star.
Supernova
A supernova (plural supernovae) is the final, gigantic explosion of a super giant star. At the end of its life, is a supernova lasts for just a week or so, but shines as a galaxy of 100 billion ordinary stars. Supernovae happen when a super giant star uses up its hydrogen and helium fuel and shines, creating pressure in its core enough to fuse heavy elements, such as iron. When iron begin to fuse in its core, a star collapses instantly –then rebounds in a mightily explosion.
Supernovae are so bright that at least five of them were seen with naked eye, before the invention of telescope.
What do you understand by global warming?
Global warming is an increase in average temperature of the earth’s surface, leading to widespread impacts ranging from change in rainfall patterns, changes in climate, melting of glaciers and polar caps, scarcity of food and water rise sea levels leading to floods, frequent hurricanes and tornadoes, onset of diseases and mass extinction of life.
Normally when the sun’s rays pass through the atmosphere, most of them are absorbed by the earth’s surface, and some are reflected back into space.
Global warming occurs when some of the sun’s rays reaching the earth’s surface are kept within the atmosphere, which raises the earth’s temperature.
The earth’s atmosphere is made up of gases, such as carbon dioxide, that trap the earth the heat from the sun. Without these gases, the sun’s heat would escape into space, and the earth would be a lot colder. These gases are known as greenhouse gases because they keep heat in the atmosphere in a way similar to how heat builds up in greenhouse. For the past 10,000 years the earth has had a relatively stable temperature.
In the last 50 years, the balance of these greenhouse gases has been upset by human activity, like burning fossil fuel such as coal and petrol. The amount of carbon dioxide has gone up by 30% and is expected to go up by another 30% in the next 50 years. A rise in greenhouse gases would result in trapping of more of sun’s heat than the earth needs and thus rise in earth temperature.
There is now worldwide awareness to take measures reduces emission of carbon dioxide. Earth day is celebrated around the world on 22nd April to create global awareness to save the earth.
Temperature increase is likely to go up 2.4 degree cilices to 6.4 degree cilices by 2100 leading to global havoc as mentioned above.