Here’s a yacht making landfall on an ironbound coast with no GPS. The Skagerrak was full of fog and although it’s clear now, she’s no idea where she is, other than off the coast of southeast Norway. All she can see is rocks, islands and a small white lighthouse, but the shoreline is studded with these. Which one is it? Choose wrong and she’s done for.
So she hove to, waited until the sun was abeam of a line that would take her straight at the rocks, and took a good sight. Astro position lines run at 90 degrees to the direction of the heavenly body, so this one was going to cut the shore at right angles. On the chart, it passed straight through one particular lighthouse. Out on deck, her skipper looked down the compass bearing of the position line and there was the structure. Problem solved. Set course, and it’s in for a cocktail before dinner!
Who says astro is only for museums?