Altitude-Intercept Method

Until the age of satellite navigation ships usually took sights at dawn, during the forenoon, at noon (meridian transit of the Sun) and dusk.

The morning and evening sights were taken during twilight while the horizon was visible and the stars, planets and/or moon were visible, at least through the telescope of a sextant.

Two observations are always required to give a position accurate to within a mile under favourable conditions. Three are always sufficient.