Atoms resonate at extremely consistent frequencies. Atomic clocks work by measuring the electromagnetic signal emitted by excited atoms and using this as a timekeeping standard – they are the most accurate clocks known. Pictured are the two active hydrogen masers located in a basement at ESA's ESOC operation's centre, installed in a dedicated temperature and humidity-controlled maser room. Masers produce 'coherent' electromagnetic waves and are used as the timekeeping device in atomic clocks.
Since November 2021, ESA’s satellites and ground stations have been running on a newly defined, incredibly precise “ESOC time”. Measured by these two atomic clocks, the new time determination will bring wide-reaching operational benefits for all ESA missions, making new feats possible in space while adding to our global definition of ‘now’.