From Sam Edge, Ringwood, Hampshire, UK
I read with interest about the “insect-eye” compass that can navigate by the sun even on cloudy days. While I can see a use for it in drones, it is relatively easy to compensate for the magnetic fields drones generate, and hence conventional systems can work. Where it may come in handy is for manual or autonomous navigation at high latitudes where Earth’s magnetic field at the surface becomes closer to vertical and begins to give less and less information about horizontal direction (2 December, p 12).
Indeed, there is some (albeit disputed) evidence that early northern European navigators, such as the Vikings, used natural crystal polarisers to determine the direction of the sun when visibility was too poor for it to be seen.
