Finding the Way

Finding the Way

Where am I? At sea, with no landmarks, it is the hardest question.

Dead reckoning. Known speed, heading and time give an estimated position.

Latitude. Measure the sun or Polaris above the horizon: quadrant, octant, sextant.

Longitude. It needs exact time. 1761: John Harrison's H4 sea watch keeps time well enough on a voyage to Jamaica.

Radio. From the twentieth century, radio beacons, then LORAN.

Satellites. GPS becomes fully operational in 1995.

Today. GNSS, radar and ECDIS, and the rule that a navigator must still be able to fix a position without them.

Try it. Take a noon sight with the sextant on the gallery's artificial horizon.

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