Wednesday, June 3, 2015

How to do celestial navigation - GPS didn't always exist

Celestial navigation is how you find your location if you are unlucky enough to live in an era before GPS or if you're in a war zone and the enemy is jamming your signals.

To do it well, you need the following:
  • a sextant
  • a marine chronometer
    • This needs to be very accurate. For every 4 seconds it is off of UTC, your position will be off by one mile.
  • a non-cloudy sky with one of the following
  • a marine almanac which gives schedules for the locations of celestial objects
  • sight reduction tables (these help with the computations so that only addition and subtraction are required)
  • a chart of the region
Now take the following steps (see Altitude-Intercept Method):
  • Find the altitude above the horizon of the celestial object (sun, moon, or star) using the sextant as instructed in this video (or the animated image above). As soon as you find the altitude, record the current time (to the second).
  • Look up the sun's position in the almanac.
  • Pick an assumed position (a rough estimate of where you think you might be).
  • Refer to the sight reduction tables to find out how far off you are from where you think you are.
  • This should allow you to determine your exact current position.

The following gives an overview of the entire process:

And this one actually gets into the nitty gritty:

  • celestial sphere
    • the surface of the heavens as seen from Earth.
  • celiac disease
    • alleviated by low gluten diet. (Apparently there is at least one real condition associated with eating gluten.)
  • La Celestina
    • Greatest work of early Renaissance in Spain. Involves a disastrous love affair. At first I assumed it would be a Romeo and Juliette type of love affair, but it turns out that there are more deaths and only one of the people commits suicide.

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