> The scientists say their model of inner core movement also explains the variation in the length of day, which has been shown to oscillate persistently for the past several decades.
How do we measure persistent changes to the length of a day on Earth? This seems like a maddeningly slippery problem.
- Geosynchronous sattelites? What if they're slightly off?
- Star readings? Can we measure that precisely enough from the surface to find tiny fractions of change?
- Any surface-based reading also has to deal with the non-spherical nahure of Earth, and its wobble (the motion that gives us seasons)
How do they do it?