Editing Space diagonal (section)

{{Short description|Line connecting two vertices that are not on the same face}}
[[Image:Cube diagonals.svg|thumb|right|250px|AC' (shown in blue) is a space diagonal, while AC (shown in red) is a [[face diagonal]].]]
In [[geometry]], a '''space diagonal''' (also '''interior diagonal''' or '''body diagonal''') of a [[polyhedron]] is a line connecting two [[vertex (geometry)|vertices]] that are not on the same [[face (geometry)|face]]. Space diagonals contrast with ''[[face diagonal]]s'', which connect vertices on the same face (but not on the same [[edge (geometry)|edge]]) as each other.<ref>William F. Kern, James R Bland,''Solid Mensuration with proofs'', 1938, p.116</ref>

For example, a [[pyramid (geometry)|pyramid]] has no space diagonals, while a [[cube]] (shown at right) or more generally a [[parallelepiped]] has four space diagonals.