Longitude
Videos
Longitude is a geographic coordinate that specifies the east-west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees
The clockwork in John Harrison's H4 marine chronometer on display at the Royal Observatory, Greenwich
Marine sandglass MMM
Geodesy
Videos
Geodesy or geodetics is the science of measuring and representing the geometry, gravity, and spatial orientation of the Earth in temporally varying 3D space. It is called planetary geodesy when studyi
Geoid, an approximation for the shape of the Earth; shown here with vertical exaggeration (10000 vertical scaling factor).
Height measurement using satellite altimetry
GPS Block IIA satellite orbits over the Earth.
Geodetic control mark