Briefly: This is a cloud formed by a Russian Soyuz rocket as it rose through the thin air of near space on the morning of Tuesday 8 July. The cross, right at the top of the formation, was made by the Soyuz’s four boosters, as their plumes ballooned out in the thin air. [Roscosmos via New Scientist]
Not A Jellyfish. Nor A Sperm.
