Astatine occurs naturally, constantly produced by the decay of uranium and thorium. But it vanishes so fast that only a few tens of grams at most exist in the entire Earth's crust at any moment. Worse, a visible sample would be vaporised by the heat of its own radioactivity. What it looks like is still a guess.
Cooled below −183 °C, oxygen turns into a pale blue liquid. Pour it between the poles of a strong magnet and, instead of flowing away, it hangs suspended between them. The reason lies in its unpaired electrons, which respond to the magnetic field. Liquid nitrogen, by contrast, is colourless and pours straight through.
In 2012, Felix Baumgartner jumped from a capsule hanging beneath a balloon, about 39 kilometres up. In that extremely thin air almost nothing slowed him down, and he reached around 1,358 km/h in free fall, or Mach 1.25. He became the first person to exceed the speed of sound with nothing but his own body.