Milky seas, or
mareel, is a condition on the
ocean where large areas of
seawater (up to ) appear to glow brilliantly enough at night to be seen by satellites orbiting Earth. Modern science only tentatively attributes this effect to
bioluminescent bacteria or
dinoflagellates, causing the ocean to uniformly glow an eerie blue at night. However, there is no modern research to prove that bioluminescent bacteria are capable of illuminating the ocean from horizon-to-horizon and for days at a time, as described in
mariner's tales for centuries (notably appearing in chapter 23 of
Jules Verne's
Twenty Thousand Leagues Under the Sea); and, in fact, the effect has not been rigorously documented nor thoroughly explained, even in modern times.