page_title: List of common misconceptions
section_title: Astronomy
hierarchical_section_title: List of common misconceptions / Science / Astronomy
caption_attribution_description: A satellite image of the Great Wall of China. This Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sub-image covers a 12 × 12&#160;km (7.5 × 7.5&#160;miles) area in Northern Shanxi Province, China, and was acquired January 9, 2001. The low sun angle and light snow cover highlight a section of the Great Wall, visible as a black line running diagonally through the image from lower left to upper right. The Great Wall is more than 2000 years old and was built over a period of 1000 years. Stretching 7240&#160;km (4500&#160;miles) from Korea to the Gobi Desert, it was first built to protect China from marauders from the north.
context_page_description: This is a list of popular wrong ideas and beliefs about notable topics. Each has been discussed in published literature.
context_section_description: It is commonly claimed that the Great Wall of China is the only human-made object visible from the Moon. This is false. None of the Apollo astronauts reported seeing any specific human-made object from the Moon, and even earth-orbiting astronauts can barely see it. City lights, however, are easily visible on the night side of Earth from orbit. Shuttle astronaut Jay Apt said "...the Great Wall is almost invisible from only 180 miles up".
  Black holes, contrary to their common image, do not necessarily suck up all the matter around them. Were the Sun to be replaced by a black hole of the same mass, then the orbits of all the planets surrounding it would be unaffected. This is because "if you're outside the event horizon, you can just keep going around in circles around [a black hole], in exactly the same way that you can be in orbit around any other kind of mass".
  Seasons are not 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 the result of the Earth being tilted on its axis by 23.4 degrees. As the Earth orbits the Sun, different parts of the world receive different amounts of direct sunlight. When an area of the Earth's surface is oriented perpendicular to the incoming sunlight, it will receive more radiation than it will when it is oriented at an angle to the incoming sunlight. In July, the Northern Hemisphere is tilted towards the Sun giving longer days and more direct sunlight; in January, 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.
  Meteorites are not necessarily hot when they reach the Earth. In fact, many meteorites are found with frost on them. A meteorite has been in the near-absolute zero temperature of space for billions of years, so the interior of it is very cold. A meteor's great speed is enough to melt its outside layer, but any molten metal will be quickly blown off, 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 them time to cool down.
caption: A satellite image of a section of the Great Wall of China, running diagonally from lower left to upper right (not to be confused with the much more prominent river running from upper left to lower right). The region pictured is 12 × 12 km (7.5 × 7.5 miles).
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