The correct answer is A) your horizon to your zenith. When working out a local apparent noon sight, the 90° represents the angular distance from the observer's horizon to the observer's zenith (the point directly overhead). This is because the local apparent noon is the time when the Sun is at its highest point in the sky, directly above the observer's meridian (the imaginary line running from north to south through the observer's position). Subtracting the observed altitude of the Sun (Ho) from 90° gives the observer's latitude, as the Sun's altitude at local apparent noon is equal to the observer's latitude. The other options are incorrect because they do not accurately represent the relationship between the 90° angle and the local apparent noon sight calculation.