Who invented the first eye chart? The first widely used eye chart was invented by a Dutch ophthalmologist called Herman Snellen. The earliest eye charts were invented in the early 19th century, but Snellen’s chart was the one that became the standard. The majority of people will have used an eye chart at some time. […]
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Why do some lakes have no fish? Some lakes have no fish because the environment they are in, or the composition of the water, is too harsh for the fish to survive. A related question is how some completely isolated lakes have fish. Most lakes contain fish. The few that don’t are usually too inhospitable
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What are the dark patches on the moon? The dark patches on the moon are called lunar mare, and they are large flat plains formed by ancient lava flows. The word mare comes from the Latin word for sea because the mare look like giant seas. A lot of people talk about the man in
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What was the Aberfan disaster? The Aberfan disaster was a terrible coal-waste landslide in 1966 that hit a school and killed 116 children and 28 adults. Aberfan is a small village in the area of Merthyr Vale in Wales, UK. The village was mostly a tiny hamlet until the Merthyr Vale Coal Mine was opened
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How do birds ride thermals? Birds ride thermals by flying in tight circles and by having specialized feathers and wings. Some birds, such as eagles, are able to make use of thermals and fly to great heights without using much energy. If a bird wanted to fly to a height of 3 km, it would
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Why are leaves different shapes? Leaves are different shapes because of the conditions they have evolved to survive in. That might be for catching more sunlight, for saving water, to not be eaten by predators, or for staying cool. Leaves on a plant or a tree are a constant tradeoff. The main purpose of a
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How were the Terracotta Warriors found? The Terracotta Warriors were found accidentally by farmers digging a well. The Terracotta Army was buried in 221 BC and it wasn’t uncovered again until it was found by farmers in 1974. There was a bad drought in the area, and Yang Zhifa and his five brothers were desperate
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]Why did the English Civil War happen and why did the Interregnum only last 11 years? The English Civil War happened because King Charles I and Parliament couldn’t agree on the balance of power, finances, and religion. The Interregnum only lasted 11 years because Oliver Cromwell’s son, Richard, was not a good enough leader to
How did we work out the age of the Earth? The age of the Earth has been calculated by looking at the oldest minerals here on Earth, rocks on the moon, and meteorite rocks. The Earth formed roughly 4.54 billion years ago. However, that is a date people have only known with certainty since 1953,
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What are the differences between a brown, red, orange, yellow, blue, white, and black dwarf? The main difference between them is their state of stage of life. Red, orange, and yellow dwarf stars are living stars. Brown dwarfs are failed stars. White and black dwarfs are dead stars. Blue and black dwarfs are theoretical because
