As the U.S. prepares to return to the moon, scientists are working to refine timekeeping in space. The moon will soon have its own time zone.

On Monday, the European Space Agency (ESA) launched the ACES set of atomic clocks to measure the effect of gravity on the passage of time.

ESA's Atomic Clock Ensemble in Space (ACES ... of ESA's Columbus module on the International Space Station, measuring time from orbit with unprecedented precision. Earlier this month, ACES ...