September 1, 2020

The spherical triangle

During the discussion of the celestial sphere last year, we discussed the spherical triangle PZX which was formed by the projected positions of the celestial pole (P), the observer’s zenith (Z) and the celestial body (X), on the celestial sphere. It was stated that the solution of this triangle formed […]
September 1, 2020

The Marcq St Hilaire method of sight reduction

In the Marcq St Hilaire method, a calculated zenith distance or altitude is compared with the observed zenith distance or altitude to obtain an intercept which is plotted from a DR position in the direction of the body’s true bearing. In explaining this method, the altitude and not the zenith […]
September 4, 2020

Alternative method of obtaining the sun’s azimuth.

In sub-paragraphs h to k of the procedure, the true bearing is obtained through the use of the A, B, C tables in Nories. There is an alternative method of determining true bearing, namely by calculation. There are two formulas that could be used: Sine formula. In order to convert […]
September 5, 2020

Astro running fixes

When using the observation of heavenly bodies to determine geographical position, a “day’s work” for a navigator comprises five sets of astro sights (provided the weather is cooperative): During morning nautical twilight the navigator will take the sextant altitudes of at least three or four heavenly bodies and using this […]
September 7, 2020

The azimuth

In order to determine the error of the gyro or magnetic compass by astronomical observation, one must be able to find the true bearing of a celestial body from the observer at any time. By comparing the compass bearing with the bearing calculated at a specific time, one can determine […]