# If a spacecraft is orbiting around the Moon, what direction would the nadir axis be?

Nadir for a craft orbiting the Earth would be radially in, is nadir always pointed towards the Earth or is it pointed towards the celestial body that the craft is orbiting?

## 1 Answer

Nadir is always pointed down to the object below. In more rigorous terms the nadir at a given point is the local vertical direction pointing in the direction of the force of gravity at that location. (see for example Wikipedia , Merriam Webster)

For a satellite orbiting the moon, the nadir vector would point at the moon surface. For a satellite orbiting Mars it would point at the Mars surface.

• @uhoh ok, added some sources – NvdP Jul 2 '18 at 5:05