Choosing the stars

Before twilight, list the stars that will be up, with their altitude and bearing (Pub. 249 Vol. 1 lists seven; a star finder, on the next pages, shows them all). Choose three or four that are:

• between 15° and 65° high: lower and refraction is unreliable, higher and the sextant is hard to swing;
• spread round the horizon: three about 120° apart, so the lines cross well and a constant error cancels;
• bright, and in the darker part of the sky first (east in the evening, west in the morning).