5 replies to this topic

[tedbnh]

Hi all,

I've been asked to give a talk on Astronomy to a local boating group, a combined sail/power squadron, after their annual dinner this February.

The talk is to be mostly on Astronomy, but since Celestial Navigation is so important to mariners I would like to include some basic material. Some of the members are well versed in CN, but others not so much. The organizers would be pleased if I included some basic introductory navigation material.

I think I can do a pretty good job on the basics - general astronomy introduction, the scale of things, how/why stars move across the sky with time and constellations change over seasons, how star (and Sun) height varies with latitude, even a bit about the need to accurately measure time to get a good fix on longitude (thanks entirely to reading the book of the same name by Dava Sobel.)

However, if anyone has any introductory material on actual CN techniques I would greatly appreciate any offers to share same. Powerpoint format would be convenient but not required. Animations will be especially welcomed!

I will be happy to make the final PPT presentation available to anyone who requests it, as I already do for my pre-skywatch presentations.

Thank you, and happy New Year!
Ted

[Skylook123]

I don't know how much time you have for your presentation, but one topic hidden in the material is that cultures since the dawn of humanity have looked to the sky to understand their world, and the original land based nomads and traders developed navigation along with the sea fairing populations. It might be worth a moment or two talking about how it has been "natural" for cultures look up for answers and guidance, whether on land or sea. I would imagine that there is some material out there on the use of the sky by the early Arabic traders, and several thousand years ago noting the precession of the Pole. Might make an interesting introduction.

[tedbnh]

Jim, that's a good idea, thanks. The talk will be 40 minutes at most, probably 30-35 with Q&A time.

Ted

[AlBoning]

Years ago I taught myself how to reduce a sight using "Sky and Sextant - Practial Celestial Navigation" by John P. Budlong.

Required equipment is a sextant (I purchased an inexpensive plastic one), an artificial horizon (too far inland for a true horizon), a reliable timepiece (started keeping track of my digital watch and still do to this day, it loses 1 second every eight days), and copies of "The Nautical Almanac" and "HO 249."

In a sense, celestial navigation is like a 3-Star Alignment of a GoTo Mount. One needs to be able to identify well placed navigation stars to ensure good results. Some interesting things learned astronomy related were that a sight taken on the Sun at local apparent Noon allows one to calculate the latitude without knowing the time; that both the Sun and Moon undergo significant changes in their apparent diameters as a function of distance; and that due to refraction by the atmosphere the apparent altitude of a celestial body changes with it's altitude.

The "Assumed Position Method" begins with just that an assumed position. One uses the sextant to measure the altitude of the navigation stars, one uses the time piece and "The Nautical Almanac" to determine what the actual altitudes observed should have been from the assumed position and their actual Lat and Long at the time observed, then one calculates the distance from the assumed position to the Lat and Long of each navigation star, draws arcs with these radii centered on the respective Lat and Long, the arcs intersect as a triangle, (the origin of the expression "in a cocked hat"), and the center of the triangle is one's current postion.

[ebusinesstutor]

I heard a speaker talk about how the Vikings navigated using notches cut on wood on their ships and using sunstones.

And he also discussed the Polynesians used songs to remember star names and locations to help them cross thousands of miles of ocean unerringly.

Two really cool examples.

[tedbnh]

Thank you all for the suggestions!

The talk went very well. Many of the members had already completed (or started) their training for Celestial Navigation certification, so it was like talking to fellow astronomers with a different accent.

If anyone would like a copy of the PPT and associated GIF and AVI files, just send me a PM and I'll send you a link to dropbox where you can download it.