Grade 11 – Nautical Science

October 15, 2020

Mercator sailings

Scale of a Mercator chart. Because the equator is shown on a Mercator chart as a straight line of definite length and the meridians appear as straight lines perpendicular to it, the longitude scale is fixed by that length and is constant in all latitudes. The latitude scale, on the […]
October 20, 2020

Astro navigation – the celestial sphere

Introduction. Astro-navigation is based upon the concept of the “celestial sphere”. What is the “celestial sphere”? If one looked up into the night sky one would see what would appear to be an enormous black dome with all the heavenly bodies stuck to the inside like thousands of diamonds. This […]
October 20, 2020


Declination.  Declination corresponds to terrestrial latitude and is defined as the angular distance of a heavenly body north or south of the celestial equator, measured in units of arc (ie degrees, minutes and seconds).  Declination is the result of the earth’s movement/orbit around the sun and the fact that the […]
October 20, 2020

Hour angle

Since the declination gives us the “latitude” of the heavenly body we must now find it’s “longitude”. We do this by measuring the angle between the celestial meridian passing through the body and that running through the observer’s position. The hour angle is defined as “the angle between the meridian […]