[ELI5] with what respect are the heights of mountains and volcanoes measured on other celestial bodies?

Question

On earth, the height of a mountain is measured from mean sea level. But how is height of mountains measured on moon where there is no water ?

In: 2

Answer 1

They use 1,737,400 meters from the centre of the Moon as the average surface level. Mt Huygens is about 5,500m above that line and considered the tallest mountain. The Selean summit has a 6,500m base to summit, but starts below the 1,737,400m surface designation, so not the tallest mountain.