Science feed
O₃
Ozone contains three oxygen atoms per molecule, while ordinary oxygen gas contains two. The extra atom changes the molecule's chemistry and explains why ozone is not interchangeable with breathable oxygen.
0.01°C
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.
Low contrast
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.