A new atomic clock in space could help us measure elevations on Earth

To prevent such costly construction errors, in 2015 scientists in the International Association of Geodesy voted to adopt the International Height Reference Frame, or IHRF, a worldwide standard for elevation. It’s the third-dimensional counterpart to latitude and longitude, says Sanchez, who helps coordinate the standardization effort. Now, a decade after its adoption, geodesists are looking to update the standard—by using the most precise clock ever to fly in space. That clock, called the Atomic Clock Ensemble in Space, or ACES, launched into orbit from Florida last month, bound for the International Space Station. ACES, which was built by the European Space Agency, consists of two connected atomic clocks, one containing cesium atoms and the other containing hydrogen, combined to produce a single set of ticks with higher precision than either clock alone. Pendulum clocks are only accurate to about a second per day, as the rate at which a pendulum swings can vary with humidity, temp ... Read full article.