It also allows a successful observation under some conditions where the solution to an altitude observation is highly unstable. Also, some extra work is required to determine adequate longitude. Time of pointing. Horizonal angle between the Sun and the line. Not highly critical for time.
Refraction is a function of the observed pressure and temperature.
The advantages of the altitude method include a minimal need for accurate time or determination of longitude. The disadvantages are that it requires a more complex pointing procedure to obtain both the horizontal and zenith readings to the Sun, and it requires some determination of atmospheric conditions in order to figure the refraction correction. In addition the refraction determination is to some degree an educated guess. Discussion Primary Difference . The primary difference between the methods comes down to the fact that the hour angle requires extraordinary care in determination of time, whereas the altitude requires extra care and skill in determination of the altitude.