PTE Core Reading Test 8

For centuries, navigators relied on the stars to find their way across vast oceans. By measuring the angle of certain stars above the horizon, sailors could estimate their latitude with surprising accuracy. Determining longitude, however, proved far more difficult and remained one of the greatest scientific challenges of the age. The problem was essentially one of timekeeping. To calculate longitude, a navigator needed to compare the local time, which could be established from the position of the sun, with the time at a fixed reference point such as a home port. Each hour of difference corresponded to fifteen degrees of longitude. The difficulty lay in keeping accurate time at sea, since the pendulum clocks of the era were thrown off by the constant motion of a ship, as well as by changes in temperature and humidity. Many lives and fortunes were lost to ships that ran aground because their crews could not determine their position. The breakthrough came in the eighteenth century when a self-taught clockmaker named John Harrison devoted decades to building a marine chronometer that could keep precise time despite harsh conditions. His invention eventually transformed navigation, allowing sailors to fix their longitude reliably and travel with far greater safety. Although satellite systems have long since replaced the chronometer, Harrison's achievement remains a landmark in the history of science and exploration.

According to the passage, why was determining longitude so difficult?

1. A.The stars could not be observed clearly from a moving ship.
2. B.Accurate timekeeping at sea was hard to achieve with the clocks of the era.
3. C.Sailors did not understand the relationship between time and longitude.
4. D.Latitude and longitude required entirely different navigational instruments.

The correct answer is shown in your review when you finish the test.