A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Frequently Asked Questions -- in need of answers!
From: Dan Allen
Date: 2003 Oct 13, 15:42 -0700
From: Dan Allen
Date: 2003 Oct 13, 15:42 -0700
Here is a starting list of questions for our FAQ. They could be better organized (I'm working on that) and of course they need to be answered! I propose the following process: 1) people write answers and send the answers to me. 2) I begin to organize them by topic and create a single HTML page that contains the questions and answers. 3) People look at the page and argue/discuss/correct/add to the questions until we're happy with them. 4) Our 1.0 version of the FAQ is done. Our challenge will be to have brief answers. Also, in order that the document can easily be downloaded or printed, all answers should be inline in the FAQ. If the answer deserves a 40 page treatment, the short answer should be given; a link to a website with a longer answer is acceptable, but a answer should not just be a link to another page. Web pages have a tendency to disappear and to be unavailable, so the FAQ needs to be self-contained. Here is my first stab at a list of questions. Please contribute better wording, removal of redundant questions, breaking of large questions into many smaller questions, better organization, different topic heads, etc. I think we want to have about 4-12 different topic headings for readability. --- BASICS What is non-electronic navigation? What kind of accuracy is needed to be able to navigate from point A to point B? What is dead reckoning? What is celestial navigation? What are the tasks in a celestial navigator's workday? What tools do I need for celestial navigation? Why celestial navigation when a GPS is so much easier, cheaper, more accurate, and faster? What kinds of instruments are used to navigate? MAPS & CHARTS Why use a Mercator chart? What is the difference between a great circle and a rhumbline? What chart shows great circles as straight lines? What is a map datum? What is geodesy? what is the geoid? What is an oblate spheroid? Where can free nautical charts be found? SEXTANTS What kinds of sextants are made? Which sextant should I buy as a first time buyer? What is the difference between a sextant and an octant? a quintant? What makes a good emergency sextant? How do you check out a used sextant to see if it is in decent shape when considering one for purchase? How do you determine a sextant's index error? SIGHT REDUCTION What is sight reduction? What are the coordinate systems used in celestial navigation? What are the main methods of sight reduction currently in use, and supported by readily available tables? What calculators/PDA's are useful for celnav, and what software is available for them? How do celestial navigators measure longitude using the moon? How do celestial navigators measure longitude using an accurate clock? How do you correct for a close horizon? What are the smallest sight reduction tables made? What is a running fix? TIME What is UTC? GMT? UT? What is sidereal time? What is right ascension? What is Greenwich Hour Angle? What is the equation of time? What kind of clocks do I need for celestial navigation, and how do I set them? Which wrist watches have the highest accuracy for use in celestial navigation? What is twilight? How can you tell time without a clock if you have a sextant? (lunars...) HISTORY Who invented the sextant? Who invented the nautical almanac? Who invented lunars? Who was Harrison and where are his clocks? Who was Nevil Maskelyne and what did he start? What is an Astronomer Royal? What men have held this office? Who was Nathaniel Bowditch and what did he write? Who are the most important historical contributors to navigation? What is the timeline for the history of navigation at sea? How did sailors find their position using latitude before they could measure longitude? How did Sumner discover the celestial line of position? What is the Saint-Hilaire intercept method? Why are Ageton's tables (H.O. 211) so compact? What are the advantages of H.O. 214? What are the advantages of H.O. 229? What are the advantages of H.O. 249 and the Air Almanac? FORMULAS What is the difference between precision and accuracy? How do you calculate the distance between two points? How do you calculate the distance between two points on a oblate spheroid? How do you calculate the closest point of approach of two moving vessels? How do you calculate your position from two bearings? How do you calculate the distance to the horizon? How do you calculate refraction? How do you calculate the equation of time? How do you create your own long-term almanac? How do you calculate areas on a sphere? What is the spherical law of cosines? How do you calculate errors using cocked hats? WHERE DO I GO FROM HERE? Where can I buy a good sextant? What are some good books on celestial navigation? What are some good web resources on celestial navigation? What are some good web/PDA resources for star identification, and provision of star ephemeredes?