For a few days either side of first and last quarter, the Moon is up in daylight well away from the Sun. Two sights a few minutes apart, one of each, give two lines that cross at a good angle: a fix without waiting for twilight.

The sky from N 38°, W 70°, March 12: zenith in the middle, horizon round the edge. The ring marks 15° to 65° high.

UT: 16:00
Sun: 47°11' high
Now: day
Good for sights (15°–65°): Sun, Moon
Sun and Moon lines would cross at: 70°

Sun and Moon both up: two lines of position by day, if they are well apart in bearing.

Press Play to watch the day go by: the Sun–Moon crossing angle changes as both move west.

The practice: planet sights at twilight from Ho first, then from the watch and sextant, and finally the Moon, in full.

A Sun–Moon fix by day