Columbus and Longitude

While Columbus explored the West Indies during his second visit, scientists back in Spain tried to figure out his precise location in Española. They were confused. If Columbus had reached the Orient like he claimed he had, he had traveled at least half the way around the earth. But things did not add up. Columbus’ islands were only several weeks away by ship. And he had sent back no reports about Oriental people or civilizations. Maybe he had reached only Antilla, the island they believed to be between Lisbon and Cathay? Or maybe, as a Dr. Cisnernos suggested, Columbus was in the Hesperides in the Atlantic Ocean Sea of Ethiopia.

Columbus finally sent word to Spain about his location in November of 1494, when he wrote a letter to his friend Pietro Matire d’Anghiera. Columbus stated that the north end of Española Island was situated at 26 degrees north latitude, and the south end at 21 degrees. That measurement corrected the 45 degrees north latitude Columbus reported during his first trip to the Bahamas. But it was still far off from today’s calculations of between 20 and 18 degrees north latitude. Columbus wrote nothing about how far west he had sailed? In other words, he revealed no longitudinal coordinates.

The fact is that on September 14 of that year, Columbus did figure out his approximate east-west position. However, he did not like the results, so he did not tell them to anyone. He recorded his measurements in a journal that would not be published until after his death. Let us explain.

Measuring Longitude

By the end of the fifteenth century, Scientists throughout Europe had become pretty good at using the celestial bodies [sun, moon, planets, and stars] to figure out their north-south location on Earth. However, it would be a long time before they could use them to figure out their east-west position, in other words longitude.

As we discussed in the article about Mesopotamia, mankind learned 2000 years earlier how to measure hours in a day by measuring the shadows cast by the sun. The point in time during the middle of the day when the sun was directly overhead and cast no shadow became known as noon. The Mesopotamians divided one day into twenty-four hours. As we have also noted, during Columbus’ time, a day at sea was measured from noon on one day to noon the next day – not from midnight to midnight, as we measure a day today. [How would a seaman know exactly when midnight occurred? It was dark and there were no clocks, satellites, or global positioning services available.]

Scientist had also figured out that if they divided the circumference of the earth by the 24 hours in the day, they could predict when noon would occur in one place compared to when it would occur in another place – similar to today’s twenty-four time zones. We mentioned how in 1485, King João II sent his royal astronomer, Abraham Zacuto’s protégé, José Vizinho, to the equator [probably with Diogo Cão] to test these theories at the equator. By then, geographers had moved the Meridian [zero longitude] from the Canaries to the Cape Verde Islands.

With the help of those calculations, scientists figured out that noon occurred about an hour later on Cape St. Vincent than it did on the Cape Verde Islands. Therefore, if India was half way around the world, then noon occurred about 12 hours later in India than it did at Cape St. Vincent. To convert the measurements of time to a measurement of distance, the scientists translated the 24 hours to degrees. 360 degrees divided by 24 hours equals 15 degrees per hour. But scientists were not yet sure how to translate degrees to miles.

Christopher Columbus disagreed with contemporary scientists about how many miles were in each degree because he disagreed with them about the measurement of the circumference of the earth. However, he could not argue about percentages. In other words, if Columbus was in India, then he was half the way around the globe, or 50 percent. That meant that an event that occurred in India would occur 12 hours later at Cape St. Vincent.

Here is a diagram of the globe showing the 24 hours by today’s measurements.

The handy thing about using the stars to obtain information is that scientists can observe the same thing celestial events from different places on Earth, weather permitting. Christopher Columbus knew that a lunar eclipse – lunar eclipses occurred when a full moon passed in front of the sun and blocked its rays – observed from St. Vincent could also be seen from Española. However, the time of day would be different. If a scientist observed the lunar eclipse from Cape St. Vincent at noon, then Columbus, if he were 50 percent of the way around the world, would observe the eclipse at midnight.

So, how did Columbus compare the time of day he observed a lunar eclipse from Española with the time of day a scientist observed the lunar eclipse from Cape St. Vincent? There were no phones, there was no Internet, and even the telegraph machine would not be invented for hundreds of years. But he had an answer – it came from Nuremberg.

As we already know, astronomers had been able to predict eclipses since the invention of the astrolabe over a thousand years earlier. The astronomer and mathematician Regiomontanus (1436-1476), aka Johann Mueller of Nuremberg, used the astrolabe to predict future dates and times of lunar eclipses in various places. Twenty years back, in 1474, he recorded and published those predictions in a book titled Kalendarium. The calendars, or charts, contained predictions through the year 1525. Two lunar eclipses were predicted for 1474 while Columbus was on Española: one on March 21 and another on September 14.

Columbus must have packed a copy of Kalendarium in his captain’s bag. On March 21, 1494, he took time from his busy schedule – surveying, claiming new islands, and looking for gold – to make sure he was standing at La Isabella on Española when the eclipse was supposed to occur. Unfortunately, the event happened at dusk. The change in the sun’s brilliance was too difficult to see.

Columbus had to wait five more months until the next eclipse, which was predicted for September 14, 1494. On that day, Columbus stood on a tiny island very near to Española called Isla Saona. [Columbus had named the island after the home town of his friend Michele de Cuneo.] The full moon started to dim around midnight. It was completely dark at 2:00 am. Regiomontanus had predicted the eclipse would occur [as seen from Cape St. Vincent] at 7:30 am. From this difference, Columbus figured out that Española was a little more than five and a half hours from Cape St. Vincent. That was two or three hours less than Columbus expected. Española was less than a quarter of the way around the globe from Cape St. Vincent.

Columbus recorded his observations in his journal. But knowing full well that he was not in India, he stowed the private manuscript away where no one else could see it. For the rest of his life, he did everything possible to suppress the fact that he had not reached the Indies. To make up for the discrepancy in the distance to India, he first reported to the Catholic Monarchs that the island of Española was much wider than it was. But at least twelve ship captains had already seen the island and negated his claim. Columbus then stated that “the peninsula of Cuba” was wider than it was. But as more conquistadors flooded the West Indies, they negated that claim, too.

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