Welcome to the Backbearing Astronavigation website.
In this day of GPS, chartplotters and all manner of electronic aids, many sailors, amateur as well as professional, are using less and less the traditional methods of navigation. Take the name of this website for example; Backbearing.
Traditionally, a ships 'departure' would be a position determined from a back bearing taken of the last bit of land the navigator could see. Once out of sight of land he was then solely dependent on his own skill and the accuracy of his Sextant, Almanac and Sight Reduction Tables.
Often perceived as a bit of a black art, Astronavigation, also known as Celestial Navigation or simply Astronav, is a means of pinpointing one's position on the surface of the Earth by measuring the angle between the Horizon and the Sun, Planets, Stars or Moon. It is an acquired skill, but one that gives a great deal of satisfaction when you make landfall where and when expected.
If you are already familiar with Astro Navigation, but are content to use nothing but the Sun, the Sun Almanac and Sight Reduction Tables on this site are ideal. With no extraneous data cluttering up the pages you will be able to reduce a Sunsight quickly and easily.
To make the entire Sight Reduction process as easy as possible there is even a Sight Reduction Form and Plotting Sheet for you to try. The version here was developed from the one in the Sextant User's Guide by Andrew Evans; probably the best introduction to Astronavigation on the web. Keep an eye out for his book on Single Handed Sailing which will be published later this year.
Many navigators end up developing their own sight reduction forms, and there are several variations on the plotting sheet, so find the version you're most comfortable with and adapt it to suit.
There is also an Excel Sight Reduction Spreadsheet for you to try. This spreadsheet displays intermediate results, which makes a very handy cross check of your manual sight reduction.
Once you've got the knack of taking the altitude of the Sun using your sextant, reducing that sight to obtain an Azimuth and Intercept, and finally plotting a Line of Position, you will be ready to take on the stars and planets.
The Links page will take you to some excellent websites with tutorials, guides, and even a full Astro Navigation course.
Backbearing.com is an Amazon Associate. In the right hand pane you will find links to navigation and boating related books and products, all available from Amazon.co.uk. Every purchase made helps defray the cost of hosting and maintaining this website. Thank you.
Check back every now and again. Files will be updated, errors corrected, and new material added as and when I can.
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Sight Reduction Form
Print double sided and on one side you can reduce morning, noon and afternoon sights, while on the reverse you will find a plotting sheet adapted from Andrew Evan's Sextant Users Guide. Ideal for that "Sun-run-Sun" sight. Download.
Universal Plotting Sheet
For the more traditional minded here is a Universal Plotting Sheet to try.