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-78.5°C
Dry ice turns directly from solid to gas at normal atmospheric pressure.
Dry ice is solid carbon dioxide, which changes directly into gas at normal atmospheric pressure. Its sublimation temperature at one atmosphere is about −78.5°C.
Dry ice turns directly from solid to gas at normal atmospheric pressure.
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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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