Category Our World

When do waves break?

Some sort of force or energy is needed to start a wave, and it is the wind that provides this energy in the water. Wind blows the surface layers of the sea, gradually a rolling movement of waves. As these waves near the coast, the sea-bed interrupts their rolling movement and they mount up and break onto the beach. The water inside a wave moves round and round in a circle. Near the shore, the circular shape of the wave is changed and it becomes squashed. The top of the wave becomes unstable, so when it hits the beach, it topples and spills over. On beaches with a shallow slope the waves pile up to a great height before breaking, causing surf.

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For centuries sailors have been in terror of being sucked into a whirlpool that would swallow them and their ships. Whirlpools happen when opposing currents meet.

 

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When do the oceans freeze?

In Antarctica and the Arctic, the oceans freeze because the temperatures are so low. Seawater, unlike fresh water, continues to increase in density as its temperature decreases towards freezing point (about -1.8 ). In fact Antarctica contains 90 per cent of all the ice on the Earth. Scientists have calculated that should all this ice melt, sea levels would rise by 60 m causing world-wide flooding. An accumulation of sea ice can cause an iceberg which floats in the sea because it is less dense than water.

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Over 360 million square kilometres of the Earth’s surface area are covered by oceans and seas, with the Pacific accounting for nearly 36% of the total.

 

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When does a solar eclipse occur?

 The Moon is 400 times smaller than the Sun but about 400 times closer. So we see them both as about the same size.

A solar eclipse is when the Moon blocks out the light from the Sun. This can make the day turn dark as all the light from the Sun is blocked out in a total part of the light is blocked out.

The Sun is our nearest star. It is 149.6 million km (92.9 million miles) away from Earth. It is the heat and light from the Sun that makes life on earth possible. The huge gravity pull of the Sun keeps the planets of our solar system orbiting around it.

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The daily rise and fall of the ocean’s tides occur because of the pull from the Moon and the Sun. There is a smaller pull from the Sun. when the Moon and Sun are in line there are high spring tides.

 

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When does a lunar eclipse occur?

The Earth casts a long shadow into space, and when this shadow passes over the Moon it can cause an eclipse.

A lunar eclipse can only happen during a full Moon, when the Sun is directly behind the Earth. It happens only occasionally, because the orbit of the Moon is slightly tilted and so the shadow usually misses it. Lunar eclipses can last for over one hour, but they do not completely black out the shadowed part of the Moon. Some sunlight always filters through, making the shadow look a reddish-brown colour. Eclipses can only be seen from certain parts of the world.

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The distance of the Moon away from the Earth was settled once and for all after the Apollo astronauts left a small reflector on the Moon’s surface. This distance is 384,000 km, though it varies slightly because the Moon does not have a perfectly circular orbit.

 

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When is the shortest day?

The shortest day of the year is in the winter solstice which is 21 December. When the Northern Hemisphere is turned toward the Sun, the countries north of the equator have their summer season, and the countries south of the equator have their winter season. When the direct rays of the Sun fall on the southern hemisphere, it is their summer and it is winter in the northern hemisphere. There are two days in the year when night and day are equal all over the world. They come in the spring and fall, just halfway between the two solstices. One is the autumnal equinox in September, and the other is the spring equinox in March.

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Mars is known as the ‘Red Planet’ because it is covered by a stone desert that contains lots of iron oxide, making it appear rusty red. The water and oxygen that used to exist on Mars are now locked up in these iron deposits; nowadays the planet has hardly any atmosphere.

 

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When is summer solstice?

The earth revolves around the Sun and at the same time it revolves on its own axis. As it moves around the Sun, it is also spinning like a top. If the axis of the earth were at right angles to the path of the Earth around the sun, all the days of the year would be the same length. However, the earth is tilted at an angle of 66.5 . In June the northern hemisphere is tilted towards the Sun and it receives more sunshine during a day. This is its warmest season called summer. On the 21 June the Sun is directly over the Tropic of Cancer and it is midsummer in the Northern hemisphere. This is the time known as the summer solstice.

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The Sun is the source of light and heat for the solar system. The four planets closest to the Sun are small and solid, the closest being Mercury. An asteroid belt separates these from the larger planets which are made up of gas.

 

Picture Credit : Google