Celestial Navigation Net - ZetaTalk

Columbus and Celestial Navigation
4. The Third Voyage: Some Improvements?
In 1498, Columbus sailed from Spain with six ships of supplies for the settlers on
Hispaniola. This is the only voyage on which Columbus made regular and serious
attempts at celestial navigation. However, the results he obtained were quite poor,
even by the standards of his day.
When he reached the Canary Islands, Columbus split his fleet: three ships would
sail WSW, direct for Hispaniola, while Columbus himself would take the other
three ships southward to the Cape Verde Islands, and then west. The reasons for
this maneuver are still debated.
On the passage west from Cape Verde, he made a series of observations of the
North Star to determine his latitude. According to Columbus, the North Star varied
from 5° to 15° above the horizon, depending on the time of the night. Actually the
North Star was about 3.5° from the celestial pole in 1498, so its total movement in
altitude should have been seven degrees, not ten. (This 3.5 degree figure was
known to navigators of that era trained in celestial techniques. This is evidence that
Columbus was still unfamiliar with celestial navigation.)
The island of Trinidad lies close to the coast of Venezuela, and is separated from
the mainland by two straits, which Columbus named Boca del Sierpe (serpent's
mouth) and Boca del Drago (dragon's mouth). Columbus tried to measure the
distance between these two straits using celestial observations. Here's a quote from
a letter Columbus wrote to the King of Spain:
"I found that there between these two straits, which, as I have said, face each other in a line
from north to south, it is twenty-six leagues from the one to the other, and I cannot be wrong
in this because the calculation was made with a quadrant. . . . In that on the south, which I
named la boca de la Sierpe, I found that at nightfall I had the pole star at nearly five degrees
elevation, and in the other on the north, which I named la Boca del Drago, it was at almost
seven."
The true altitudes of the North Star at these places (in 1498) would have been about
12.8° and 13.5° respectively; so Columbus's errors were about 8 and 6 degrees.
This is very poor observation by any standard. Shortly after this, Columbus took ill
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