Category Science

Why do clouds have different shapes?

               Clouds vary in shape according to their height and temperature, and they contain minute drops of water or ice particles or a combination of both. And, of course, their forma­tion is greatly affected by wind changes.

               There are basically three groups of clouds: high clouds between 17,000 and, 45,000 feet (cirrus, cirro-cumulus’ and cirro-stratus); middle clouds between 7,000 and 23,000 feet (alto-cumulus, alto­stratus and nimbo-stratus); and low clouds up to 7,000 feet (strato­cumulus, stratus, cumulus and cumulo-nimbus. Their height and temperature decide how much pressure is exerted on them by the atmosphere.

               Finally, the shapes of clouds differ according to the time of day. Towards evening Clouds tend to thin out, rise a little and flatten out.

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When does sheet lightning occur?

               Sheet lightning usually occurs during a storm as the result of a discharge of excess electricity within a single thundercloud. The outline is obscured and the result is a diffused light spread over a large area of the sky in contrast to the vivid spiral or ribbon-like flashes of chain, forked or zigzag lightning. The most favorable conditions for sheet lightning are provided when the electric field is equal throughout the area. Unlike other forms of lightning it does not reach the ground and the channel cannot be distinguished.

               What is often referred to as sheet lightning is merely the light­ing up of the sky by flashes occurring beyond the horizon.

               All lightning is the natural dis­charge of large accumulations of electric charges in the atmosphere. It may take place between neighboring clouds or between cloud and earth. Just before the dis­charge the cloud’s electric poten­tial is often built up by the action of falling raindrops or other natural processes.

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When was coffee first grown?

          A legend says the coffee plant first grew in Kaffa, a province in south Ethiopia, where it was discovered by a goatherd called Kaldi about the year 850. Kaldi’s goats were reported to have skipped and pranced in a strange manner after feeding on an evergreen plant. The goatherd, so the story goes, tried some of the berries himself and excitedly dashed to the nearest town to tell of his find, which was called coffee after the name of the province.

          Another theory is that the word coffee is probably derived from the Arabic qahwah. Certainly coffee was introduced info Europe from Arabia during the 16th and 17th Centuries. The first license to sell coffee in the United States was issued to Dorothy Jones of Boston in 1670. The coffee houses of this time became famous meeting places for discussion.

          As the drinking of coffee be­came more popular, its production spread to Java, Haiti, Dutch Guiana, Brazil, Cuba, Jamaica, Puerto Rico, Costa Rica, Vene­zuela, Mexico, Colombia, the Hawaiian Islands and, in this century, Africa.

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What is twilight?

          Twilight is the faint light which appears a little before sunrise and again after sunset before it gets really dark.

          On the moon there is no twilight. Darkness comes suddenly as soon as direct sunlight ceases to reach the moon’s surface. This does not happen on earth because of the halo of air, called the atmosphere, which surrounds it When the sun goes below the horizon, its light leaves the earth but is’ reflected downward from the upper atmos­phere.

          Poets and writers have written of the evening twilight or “the gloaming”, as it is called in Scot­land – as an enchanted time. Per­haps one reason is that familiar objects become distorted in the half-light and we imagine we are seeing things that are not really there.

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Why do river deltas form?

               A river winding its way down to the sea, from its mountain source, will inevitably choose the lowest land through which to flow. By the time the river approaches the sea the speed at which it is travelling will have decreased considerably, thus allowing the water to drop its load of sediment and other solids.

               These solid particles (alluvium), therefore, form the land pockets which are characteristics of the various branches of a river delta. Owing to the slow pace of a river at this stage, it will wind its -way round any elevated land points rather than go over them.

               Deltas are most likely to form where the sea, into which the river flows, is particularly calm for most of the year. Notable deltas in the world include the Mississippi (the largest) the Ganges, end the Nile. A delta is so called because it is the name of the fourth letter of the Greek alphabet whose shape it resembles.

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When does a geyser occur?

            A geyser occurs when a hot spring erupts, hurling a column of water and steam high into the air. These springs are situated in regions which were formerly volcanic and which have retained considerable heat near the surface.

            They usually have craters with well-like shafts penetrating into the earth. The water which gathers deep down in these shafts becomes heated until the lower part is changed into steam, the pressure of the steam steadily mounts to a point when it suddenly hurls the water above it into the air, sometimes to a height of over 100 feet.

            The chief geyser districts are in Iceland (home of the Great Gey­ser), in the Yellowstone National Park, Wyoming, United States, and in New Zealand. For four years Waimangu in New Zealand, the greatest of all geysers, was capable of spouting jets up to 1,500 feet.

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