Day and Night


Why are times different in other countries?



Clocks in other countries need to be adjusted so that it gets light and dark at approximately the same time everywhere. Without this adjustment, people might find that dawn was at 10 o’ clock in the evening, for example.



In 1884 time zones were set up around the world, measured from Greenwich in London, England. Every time zone east or west of Greenwich has noon at a different time. Each zone is either one hour ahead or behind of its neighbouring zone – it is one hour earlier to the west of each zone, and one hour later to the east.



Picture credit: google



 





 



What are the northern lights?



           The northern lights are streaks and sheets of pale, flickering, coloured lights that are sometimes seen in the night sky in far northern regions. Their proper name is the aurora borealis. The same effect also occurs in the far south, where it is known as the aurora Australis.



            Auroras take place between 97 and 1,000 km above the Earth’s surface. They are caused by electrically charged particles from the Sun. These particles strike the Earth’s atmosphere and release energy in the form of light. Auroras are most common when there are many sunspots, which increase the amount of energy released by the Sun.



Picture credit: google


Day and Night


 



Why do we have coloured sunsets?



Coloured sunsets happen when light is scattered by dust and water particles in the air, as the Sun sets. At sunset, the light passes through a much greater thickness of air, because it strikes the atmosphere at a shallow angle. The farther the light has to pass through the air, the more likely it is to be scattered by the dust particles, causing the red colouration.



 



 



 





 



 



 



Why does the Sun rise in the east?



The direction of the Earth’s rotation means that the Sun appears to rise in the east and set in the west. If you imagine that you are standing at the North Pole and looking down on the Earth, it would rotate anti clockwise. In other words, the Earth rotates towards the east, so the Sun first becomes visible from that direction.



 



 



 





 



 



 



 



What is the Earth’s axis?



The Earth’s axis is an imaginary line through the geographic centre of the Earth about which it spins. You can think of the axis as being like a stick pushed through the middle of an orange. The axis is tilted at an angle of 23.5 degree from the vertical, in relation to the Sun. We still do not know the reason for this tilt.



 


Day and Night



 



Why do we have day and night?



As the Earth spins on its axis, the Sun always shines on one side giving us daylight. It is night on the shaded side. As the Earth continues to turn, the shaded side moves into the Sun’s light and the sunlit side turns away from the light. It takes 24 hours for the Earth to make one complete turn on its axis, and our clocks are based on this principle.



In the 1940s, people discovered that the Earth speeds up and slows down a little as it spins, although the reason for these changes is not fully understood. We have now developed atomic clocks that can measure time exactly.



 



 



 





 



Why do we have seasons?



We have seasons because the Earth is tilted on its axis. As the Earth moves around the Sun, the hemisphere tilted towards the Sun receives more sunlight and this is summer time. The days are longer and the weather is warm because of the extra sunlight. The hemisphere tilted away from the Sun receives less sunshine, has shorter days and is cooler – it is winter time. The area near the Equator is always exposed to the Sun’s rays, so it is warm all the year round. This means that there is little difference between the seasons.


The Universe


What is the Milky Way?



The Milky Way is a huge mass of gas and stars that can be clearly seen as a band of light across the night sky.



            The Earth and everything else in the Solar System is part of the Milky Way. It is known as our Galaxy. It is so huge that light takes nearly 100,000 years to travel from one side to another. Where stars are packed close together the Milky Way is bright, but huge clouds of gas and dust block the light from the other parts of the Galaxy. These clouds prevent astronomers from observing the whole Milky Way.



 



 





 



 



The super supernova



Sometimes a star appears in the sky quite suddenly. This happens when there are pairs of stars rotating together. These are called binaries, and there is usually one large star called a red giant, orbiting with a smaller, hotter star. The nova takes place when gas is drawn from the red giant into the smaller star, where the heat causes a massive explosion and emits huge amounts of light. A supernova takes place when a star collapses as it begins to burn out, then suddenly explodes, producing a huge amount of light energy, and leaving behind a tiny core of neutrons, which is the heaviest substance in the Universe. A pinhead-sized mass of neutrons weighs many thousands of tonnes.



 


Continue reading "The Universe"

The Universe


 



What was the Big Bang?



The Big Bang is the most popular theory about the creation of the Universe. According to it, the whole Universe was created in a split second in one huge explosion. All matter was squeezed together into a tiny, super-hot, dense ball that was smaller than an atom. The ball gradually expanded as it cooled, then exploded, releasing energy and matter in all directions. We cannot see the Big Bang because it would have happened billions of years ago. But we can see that the Universe is growing steadily bigger. All the galaxies are speeding away from each other as the Universe expands.



 



 



 





 



 



What is the Universe made of?



The Universe is made up almost entirely of hydrogen and helium. These are the two lightest elements. All the rest of the matter in the Universe is very rare. Elements such as silicon, carbon and others are concentrated into clouds, stars and planets. The Universe is held together by four invisible forces. Gravity and electromagnetism are the two familiar forces. The other two kinds are strong and weak nuclear forces. These operate only inside the incredibly tiny nucleus of atoms, holding the tiny particles together.



 



 



 



 



 





 



 



How old is the Universe?



It is possible to calculate the approximate age of the Universe by looking at how fast distant galaxies are moving away from us. However, it is not possible for us to make this calculation accurately. Scientists have estimated that the Universe is between 13,000 and 18,000 million year old.