# How do we know pulsars have two beams?

Pulsars are neutron stars the emit a beam of electromagnetic radiation that is not aligned with their rotation axis. So we can only see a neutron star as a pulsar if the beam crosses Earth's path.

The common representation is that there are two beams, one on each side, but unless the magnetic axis and the rotation axis are at 90°, we can only ever see one of the two beams. How do we know that there are two beams and not one, or four, or any other number?