Do humans have a north sense?
20.14, Tuesday 14 Jul 2020 Link to this post
Possibly we have a sense called magnetoreception which lets us tune into the earth’s magnetic field and know where north is. Birds can do it.
Magnetoreception on Wikipedia:
For animals the mechanism for magnetoreception is unknown and its existence is controversial.
There’s some scientific evidence from 2019 that humans can detect magnetic fields: when placing subjects in an isolation chamber,
among many participants, changes in their brain waves correlated with changes in the magnetic field around them.
Humans are sensitive to polarised light:
Many people are able to perceive polarization of light. It may be seen as a yellowish horizontal bar or bow-tie shape (with “fuzzy” ends, hence the name “brush”) visible in the center of the visual field against the blue sky viewed while facing away from the sun, or on any bright background. It typically occupies roughly 3–5 degrees of vision, about twice or three times the width of one’s thumb held at arm’s length.
The blue cones in the eyes vary in sensitivity depending on their angle to polarised light, and they are arranged circularly around the centre of the eye. So when light is polarised, you get a situation where the cones at the top and bottom are reacting more/less than the cones on the left and right. Which is visible.
Polarised light is interesting because light across the sky is polarised in a particular pattern depending on the position of the sun. See: the Raleigh sky model.
Nice tidbit from that article:
It has been suggested that Vikings were able to navigate on the open sea in a similar fashion, using the birefringent crystal Iceland spar, which they called “sunstone”, to determine the orientation of the sky’s polarization. This would allow the navigator to locate the sun, even when it was obscured by cloud cover. An actual example of such a “sunstone” was found on a sunken (Tudor) ship dated 1592, in proximity to the ship’s navigational equipment.
So maybe we unconsciously tap into a natural ability to sense polarised light, which is to say a sense of where the sun is, and so end up with a sense of north?
BONUS LINK only for the fans who got to the bottom.
Dogs tend to poop aligned north-south. It’s probably because they’re sensitive to the earth’s magnetic field rather than polarised light. How do the scientists know? Because during magnetic storms, dogs poop any which way.
Hart, V., Nováková, P., Malkemper, E.P. et al. Dogs are sensitive to small variations of the Earth’s magnetic field. Front Zool 10, 80 (2013).