An Egyptian astronomer would have held up a plumb line and waited for the night sky to slowly pivot around the unmarked pole as the Earth rotated.

BBC: Pyramids lined up with the stars

Ben Kingsley, now sixty, is in great shape his carriage is so erect that you could drop a plumb line from the back of his bald crown to his heel.

NEWYORKER: House of Sand and Fog

When the plumb line exactly intersected both stars, one about 10 degrees above the invisible pole and the other 10 degrees below it, the sight line to the horizon would aim directly north.

BBC: Pyramids lined up with the stars