Note 64 — Chapter III

Chauvenet (Spherical and Practical Astronomy, Vol. I, p. 283) shows that when both latitude and time are required, the three stars should differ in azimuth by 120° to give the most accurate results. But when only the latitude is required the stars are best selected near to the meridian north and south of the zenith. This is evident by considering that if two stars could be observed to culminate at the same altitude on opposite sides of the zenith, the latitude would be precisely determined independently of any reference to time.