Common Scientific Myths -- Astronomy

Astronomy

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• It is commonly claimed that the Great Wall of China is the only man-made object visible from the Moon. This is false. None of the Apollo astronauts reported seeing any man-made object from the Moon. The misconception is believed to have been popularized by Richard Halliburton decades before the first moon landing.
• Black holes, unlike the common image, do not act as cosmic vacuum cleaners any more than do other stars. When a star evolves into a black hole, the gravitational attraction at a given distance from the body is no greater than it was for the star. That is to say, were the Sun to be replaced by a black hole of the same mass, the Earth would continue in the same orbit (assuming spherical symmetry of the sun). Due to a black hole's formation being explosive in nature, the object would lose a certain amount of its energy in the process, which, according to the mass–energy equivalence, means that a black hole would be of lower mass than the parent object, and actually have a weaker gravitational pull.
• When a meteor lands on Earth (after which it is termed a meteorite), it is not usually hot. In fact, many are found with frost on them. A meteor's great speed during entry is enough to melt or vaporize its outermost layer, but any molten material will be quickly blown off (ablated), and the interior of the meteor does not have time to heat up because rocks are poor conductors of heat. Also, atmospheric drag can slow small meteors to terminal velocity by the time they hit the ground, giving the surface time to cool down.
• It is a common misconception that seasons are caused by the Earth being closer to the Sun in the summer than in the winter. In fact, the Earth is actually farther from the Sun when it is summer in the Northern Hemisphere. Seasons are actually the result of the Earth being tilted on its axis by 23.5 degrees. As the Earth orbits the Sun, different parts of the world receive different amounts of direct sunlight. In July, the Northern Hemisphere is tilted towards the Sun giving longer days and more direct sunlight; in December, it is tilted away. The seasons are reversed in the Southern Hemisphere, which is tilted towards the Sun in January and away from the Sun in July. In tropical areas of the world, there is no noticeable change in the amount of sunlight.
• It is a common misconception that it's easier to balance an egg on its end on the first day of spring. In fact, the ease or difficulty of balancing an egg is the same 365 days a year. This myth is said to originate with the egg of Li Chun, an ancient Chinese folk belief that it is easier to balance an egg on Li Chun, the first day of spring in the Chinese lunar calendar. In Chinese Li = setup/erect; Chun = spring/egg. Setup spring is a Chinese solar term, literally interpreted as erecting an egg for fun. It was introduced to the western world in a Life article in 1945, and popularized once again by self-titled 'urban shaman' Donna Henes, who has hosted an annual egg balancing ceremony in New York City since the mid-1970s.