Sizing Up Earth

Look closely: Earth's shape and size isn't as constant as it seems.

Geodesy has evolved over two millennia from simple geometry to include an ever-expanding range of new technologies.

One geodesy technique, laser ranging, can track the precise altitude of orbiting satellites and changes in Earth's size, shape and gravity.

Scientists aim radio telescopes at distant objects called quasars and measure how long it takes their radio signals to reach Earth.

Minor time differences in telescopes' detection of radio signals from quasars are used to map fine distances and tectonic movements on Earth.

With exact coordinates provided by geodesy, scientists can monitor the elevation changes in ice sheets and sea level.