  The extended BMS group includes supertranslation, dual supertranslation and
Lorentz transformations. The generators of these symmetries can be classified
according to their parity into "electric" and "magnetic" types. Using a
multipole expansion of gravitational sources in the Newman-Penrose formalism,
we associate each one of these charges with a particular moment. At leading
order, the "electric" and "magnetic" monopole moments correspond respectively
to supertranslations and dual supertranslations. At the first subleading order,
the "electric" and "magnetic" dipole moments correspond respectively to boosts
and rotations, therefore comprising the entire Lorentz group. Electric-magnetic
type of duality then rotates the boost and rotation generators into each other.
