Thursday 4 February 2016

36 “During Captain James Clark Ross’s voyages around the Antarctic circumference, he often wrote in his journal perplexed at how they routinely found themselves out of accordance with their charts, stating that they found themselves an average of 12-16 miles outside their reckoning every day, later on further south as much as 29 miles.”

False assumption: 

All mid-19th century-explorations relied heavily on celestial navigation, which, over long distances, only works on a spherical model of earth (we'll have more on that later).

It is also known that atmospheric refraction (deviation of light through differently dense air layers) increases the further you go into polar regions because of higher gradients in temperature. 
Furthermore, there is also the huge problem of the antarctic circumpolar current, which until today is a big issue for sailors because of its high forces and speeds, however, it was not fully understood at that time.

These three facts combined provide a perfect explanation of how sailors at that time COULD circumnavigate around Antarctica, but many times experienced an offset to the position where they expected to be. Let's say you are today sailing around Antarctica and you only use a sextant for navigation. Trying to determine your position and finding yourself a little off by only 20 miles from where you expected to be, any sailor in the world will tell you that you are actually in quite good shape. It is within your margin of error.

Using these methods AND understanding these phenomena, in no way does an offset of 20 miles concern you (geometrically) as a sailor, nor does it dispute a spherical earth.

1 comment:

  1. As an additional comment to this, the accurate marine chronometer has just been invented, and so accurate longitudinal reckoning was still in it's infancy. The ONLY charts of Antarctica that had been done previous to this were done WITHOUT the advantage of the marine chronometer, and hence without the ability to reckon longitude accurately.

    So, of course the charts would not be accurate. The previous charts were using what were often incredibly complex calculations and subjective celestial observations (often using the moons of Jupiter) to estimate longitude.

    To think that charts done WITHOUT a marine chronometer would be as accurate as charts done WITH a marine chronometer is idiotic.


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