Why does ozone have a dipole moment different than 0
The electrons are not shared equally among the oxygen atoms.  The central oxygen atom alone donates three electrons to the covalent bonding whereas the other two oxygen atoms combined donate the other three (there is a 3-center, 4-electron pi bond in which two of the rlectrons are shared between just the end atoms).  Since the central oxygen atom is providing an excess of bonding electrons, it becomes positively charged.  The other oxygen atoms, contributing fewer electrons to the bonds and retaining more &quot;lone pairs&quot;, take the compensating negative charge.
Trisulfur is a similarly polar elemental species, with a bent structure and unequal electron sharing similar to ozone.  Sulfur dioxide and disulfur monoxide, the latter found along with trisulfur on the Jovian moon Io, have a similar unequally-shared-electron structure with sulfur in the middle.  But we take little notice in the latter two cases because the sulfur, being less electronegative than oxygen, would be positively charged anyway.