“It was misty, the boat was jumping like a flea, shipping seas fore and aft and there was no “limb” to the sun so I had to observe the centre by guesswork. Astronomically, the limb is the edge of sun or moon. If blurred by cloud or fog it cannot be accurately “brought down” to the horizon. The centre is the spot required, so when the limb is too blurred you bring the centre of the bright spot behind the clouds down to the horizon. By practice and taking a series of “sights” you can obtain an average that has no bigger error than one minute of arc.”

— Frank Worsley