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~78%
Nitrogen makes up about 78 percent of dry air.
Nitrogen makes up about 78 percent of dry air by volume, while oxygen contributes about 21 percent. These familiar percentages describe air with its variable water vapor excluded.
Nitrogen makes up about 78 percent of dry air.
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0.01°C
Water can boil and freeze at the same time.
Water can coexist as ice, liquid and vapor near its triple point, about 0.01 °C and 611 pascals. In a vacuum demonstration, evaporative cooling can make liquid water freeze while it is still boiling.
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Low contrast
The Great Wall is difficult to distinguish from orbit with the naked eye.
The Great Wall is generally not discernible with the unaided eye from low Earth orbit, and it is not visible from the Moon. Saying it can never be seen from any altitude called space is too absolute: viewing conditions, equipment and identification all matter.
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