When was latitude developed

The motion of a ship was the main issue preventing a pendulum clock in the 18th century from keeping time at sea. A pendulum would not swing consistently to keep time while a ship was pitching and yawing on the open seas.

John Harrison was the first inventor to work towards a viable solution to this problem. His first sea clock, H1, did not have a pendulum but two interconnected bar balances which counteracted each other, ensuring that the mechanism lost less time. H1 was a significant step towards accurately determining longitude at sea.

His next design, H4, was the culmination of more than 30 years of research to create an accurate marine timekeeper. Harrison took a dramatic design change for H4 after realising that the pocket watch offered the solution to timekeeping at sea — the compact body and robust balance mechanisms of pocket watches offered the stability a marine timekeeper needed.

Not quite! The political, social and economic implications for safer sea travel were so great at the time that the Longitude Act was passed in by Queen Anne. The importance of the longitude problem was summed up by the Act:.

This worked well locally, but different methods were needed for travelling further afield across featureless terrain such as sea or desert. Travellers now required a frame of reference, or co-ordinates, to fix their position. Over the centuries, increasingly sophisticated devices, like the gnomon and the Arabian Kamel were designed, to measure the height of the sun and stars above the horizon and thereby measure latitude.

The first instruments used at sea to measure latitude were the quadrant and the astrolabe, both of which had been used for years by astronomers to measure the inclination of stars.

To determine your exact location you also need to measure your line of longitude. Great minds had tried for centuries to develop a method of determining longitude. Hipparchus, a Greek astronomer — BC , was the first to specify location using latitude and longitude as co-ordinates. He proposed a zero meridian passing through Rhodes.

He further suggested that absolute time be determined by observing lunar eclipses, measuring the time when a lunar eclipse started and finished, and finding the difference between this absolute time and local time. However, his method required an accurate clock, something yet to be invented.

In , Gemma Frisius proposed a new method of calculating longitude using a clock. The clock would be set on departure and kept at absolute time, which could be compared with the local time on arrival. Cracking longitude was not only important for the safety of navigators, but vital for the development of sea-borne trade. In , Philip II of Spain offered a prize to any person who could provide a solution to the problem. The King remained unconvinced. As Galileo had suggested, he used the moons of Jupiter to map the world.

In , Cassini travelled to the island of Goree in the West Indies to repeat his measurements. Many eminent scientists set to work, but it was an unknown amateur clockmaker from Yorkshire, John Harrison, who rose to the challenge. He saw time as the key and realised that if you could determine local time from the position of the sun and the time at some reference point like Greenwich , you could calculate the time difference between the two. From this, you could work out how far apart the two places were in terms of longitude.

The problem was that no timepiece existed that could be set at home and relied on to keep time accurately while at sea, where pendulums were notoriously unreliable. So, even if local time could be determined from the noonday sun, there was no time to compare it against. This was the problem that Harrison set out to solve.

Despite this, Harrison was initially awarded only half the promised amount. On a voyage from England to Jamaica in —62, H4 lost just five seconds in over two months at sea. It was now possible for a navigator to determine local time by measuring high noon, and compare this to the absolute time, which had been set on an accurate chronometer at the start of the voyage.

At long last, both latitude and longitude could now be determined accurately, and for the first time you could say exactly where on Earth you were. Today, it's all done electronically through GPS, a world-wide radio navigation system made up of a constellation of 24 satellites and their ground stations.

These 'artificial stars' are used as reference points to calculate a terrestrial position to within an accuracy of a few metres. In fact, with advanced forms of GPS you can make measurements to within a centimetre! However, the Southern Cross and Centaurus constellations can be used to find the south celestial pole.

If a line is drawn through the long axis of the Southern Cross, and another line is drawn between the two brightest stars in Centaurus, the two lines will intersect at the south celestial pole. Your longitude represents the angle east or west between your location, the center of the Earth, and the prime meridian Fig. As you move east and west from the prime meridian, eventually you reach o E and W on the opposite side of the globe from Greenwich. This point is the International Date Line. Lines of longitude are called meridians of longitude, or great circles.

All circles of longitude are the same length, and are not parallel like lines of latitude; they converge as they near the poles. Therefore, while one minute of latitude always equals one nautical mile , the length of one minute of longitude will decline from the equator to to poles, where it will ultimately decline to zero.

Measuring longitude requires accurate time at your current location, and also the time at some distant point like a home port at the same instant. The time difference can be used to calculate longitude.

This is because the Earth takes 24 hours for a complete o rotation. Therefore, for each hour of time difference between two locations, there is a 15 o difference in longitude. Accurate measurements of latitude using the North Star have been made since at least the third century B. Before then, sailors would often sail north or south to get to the desired latitude, then just head east or west until they reached the target longitude.