Distance Along a Meridian
Nautical miles between two latitudes on the same meridian.
Formula
Variables
Example
Δφ = 2°: d = 120 nm
How it works
A meridian is a north-south line on the Earth, so moving along one means you are changing latitude without changing longitude. In nautical navigation, one degree of latitude is taken to be 60 nautical miles because the nautical mile is defined from the Earth's geometry and scale of latitude. So the distance between two points on the same meridian is just the latitude change in degrees multiplied by 60.
When to use it
Use this when two positions lie on the same longitude and you need the north-south distance between their latitudes. It is common in basic navigation, chart work, and estimating travel distance along a meridian.
Worked example, step by step
A ship moves from 18°N to 23.5°N on the same meridian. Δφ = 23.5° - 18.0° = 5.5° d = 60 × Δφ d = 60 × 5.5 d = 330 nm So the distance along the meridian is 330 nautical miles.
Common mistakes to avoid
- Using longitude difference instead of latitude difference
- Forgetting to take the change in latitude in degrees before multiplying by 60
- Applying the formula when the two points are not on the same meridian
Did You Know?
Each degree of latitude is 60 nautical miles — a fact that ties navigation directly to the Earth's geometry.
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