Like Saturn, Jupiter’s gaseous surface rotated quickly, with a complete Jovian day taking just under ten Earth hours. Orbiting high above the surface of the planet, it wasn’t helpful or convenient for the Endeavour residents to measure time according to Jupiter days, so the central computer divided sifts into twenty four Earth hours and ran a standardised calendar known in the Jupiter system as Jovian Standard Time.

While in theory a JST day was the same length as an Earth day, relativity would gradually throw the Jovian chronometer out of synchronisation with the Earth Calendar. To compensate, at irregular intervals during Jupiter’s solar orbit (which took twelve Earth years to complete) Endeavour’s chronometer programme would add between six and twelve leap hours, during which scheduled manual tasks were kept to a minimum while staff management programme prepared to restart. It was the closest thing the local workers ever got to a public holiday, which was fine because the nearest beaches were on Io. They were extremely cold and made from sulphur dioxide instead of water, which didn’t do much to encourage family trips to the seaside. People tended to drink a lot instead.

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