Useful Approximations

• 1 thumb's width (at arm's length) = visual angle of 1.5°
• 1 fist-width (from thumb to little finger knuckles) = visual angle of 10°
• A small buoy will be visible at 1.5 miles; its colour and shape at 1 mile
• Building windows are visible at 2 miles
• A moving person looks like a limbless black dot at a distance of 1 mile
• Faces without features can be seen at a distance of 300 metres/1000 feet.
• The shore becomes visible at 4 miles