Definition
In celestial navigation, the geographic point on a chart where two or more lines of position (LOPs), each obtained from a separate celestial observation, cross one another. The intersection is taken as the aircraft's fix — its position on the Earth's surface at the time of the observations.
Plain English
When a navigator takes sightings of two stars (or the sun and a star), each sighting gives a line on the chart along which the aircraft must be. The point where those lines cross is treated as the aircraft's position.
Context Anchor
Seen in navigation, chart reading, and position-fixing discussions, especially when a location is identified by the crossing of two bearings, courses, or other navigation references.
Derivation
Position lines (also called lines of position) are called 'designated' because the navigator chooses which celestial bodies to observe and the resulting lines are plotted deliberately. 'Intersect' is from Latin intersecare, 'to cut between' — the lines cut across each other on the chart, and that crossing point is the fix.
Why Pilots Care
Provides a reliable way to confirm position without sole reliance on GPS or visual references.
Analogy
It is like finding a town on a road map by seeing where two roads cross. The crossing point gives you a clear location, not just a general area.
Intuition Check
Do not think of these as painted lines on the ground. In navigation, position lines are imagined or charted lines that help define where the aircraft is.
Example Sentence 1
After shooting the sun and Polaris within a few minutes of each other, the navigator plotted both lines of position and marked the aircraft's fix where the designated position lines intersected.
Example Sentence 2
After drawing the lines, the crew noted their aircraft was directly at the point where the designated position lines intersect.