What is the main idea of the passage?

Reliable sea clocks helped navigators find longitude by preserving a reference time during voyages. (The passage connects the longitude problem with Harrison’s durable timekeepers and the comparison of local noon to reference time.)

Why could a difference between local and reference time reveal longitude?

Different east-west positions reach local noon at different points in Earth’s turn. (Because Earth turns, local noon occurs at different times from place to place; comparing those times indicates east-west separation.)

What does “friction” mean in the clockmaker’s work?

Resistance produced when moving parts rub against one another (Harrison reduced friction while improving a mechanism, so the word refers to resistance between the clock’s moving surfaces.)

What two conditions disturbed pendulum clocks at sea?

A rolling ship and changing temperature (The second paragraph directly identifies a ship’s rolling motion and temperature changes as problems for pendulum clocks.)

Longitude and the Sea Clock: Level 2 Reading Comprehension Questions

For centuries, sailors could estimate how far north or south they were by watching the Sun and stars. Finding longitude, their east-west position, was harder. A navigator needed to compare local noon with the time at a known reference place. Every hour of difference represented part of Earth’s daily turn.

The idea required a clock that kept accurate time during a long voyage. Pendulum clocks worked on land, but a rolling ship and changing temperature disturbed them. In eighteenth-century Britain, carpenter and clockmaker John Harrison spent decades developing sea clocks. He reduced friction, allowed parts to adjust for temperature, and eventually built a watchlike timekeeper that performed well at sea.

Harrison was not the only person studying longitude, and astronomy remained another important method. Yet reliable marine timekeepers gave navigators a practical new tool. By carrying reference time across the ocean, a clock could help turn two observations into a position on a chart.

Comprehension questions