Navigate by the stars! Sounds cool, let’s give it a try. Max has recently been practicing his sextant skills with his newly acquired instrument.
At first this sounds like an ancient and nostalgic art to determine one’s position on earth in an age where every phone or watch can give you a location accurate to a meter. However, the satellite system commonly known as GPS which gives most of our phones and other devices location coordinates only became available to civilians in 1993 (initially the US developed it during the 80s for military purposes). So until fairly recent seafarers relied on methods such as astro navigation when no land was in sight. So much so that if you want to captain a boat across an ocean commercially this skill is still a requirement today.
The concept of the sextant dates back over 2000 years to ancient Greece and the instrument saw little change in the last 250 years.
The sextant itself simply measures the angle between a body in the sky (sun, moon, stars…) and the horizon. Hence, astro navigation rarely is possible at night as being able to see the horizon is vital! Most measurements are done during twilight for planets and stars or during the day for the sun.
The simplest method is known as “noon sight” and measures how high the sun is at its highest point during the day. At that exact moment I know it is directly south from me. The position of the sun itself is known for every day, hour and minute of the year and can be looked up in a book called the Nautical Almanac. It’s the location on earth where the sun would be right above my head (or 90° to the horizon). Now that I know where the sun is at the time of my sight and that I am directly north of it I can calculate my latitude (how far north or south from the equator) based on my angle to the sun I measured with the sextant. My longitude (how far east or west from Greenwich, London) is the same as the sun as it is due south from me.
It’s fascinating how important timing is to determine longitude, but understanding why is simple. The earth does a full rotation (360°) in 24 hours or 15° per hour or 1 mile every 4 seconds. Hence, if I miss the sun’s highest point by only 12 seconds my position will be off by at least 3 miles already. This is why early explorers could tell how far north or south they were, but east or west was a guessing game. Their clocks were not accurate enough. It was only the introduction of accurate time keepers in the last 200 years which made it possible to determine longitude accurately.
A skilled navigator with a precise instrument will be able to get an accuracy of one mile. That is more than enough to navigate across an ocean and make landfall at your desired destination.
Keep in mind these measurements are done at sea while the boat is rocking. It’ll take a while to master the instrument and the theory. The goal is to fix our position with reasonable accuracy during our next crossing to Panama.
Now if you believe the earth is flat rather than a sphere this probably sounds like witchcraft! 😄
Por Que No Sailing 