The classic celestial position fix is an intercept fix, taken either at sunrise or at sunset.Įxample of the intercept method for a celestial navigation position fix. Pro Tip: I learned celestial navigation from college, but always found one book particularly useful for brushing up my skills: Celestial Navigation, by Tom Cunliffe (link to Amazon). Comparing the calculated azimuth to the compass bearing lets you calculate the error in your compass. Using a nautical almanac, you can calculate the azimuth, or bearing, of any celestial body from your position. The final use of celestial navigation is for calculating your compass error by azimuth. Combining that with your longitude at merpass, you can get a full position fix from a single sight. If you take a standard sun sight at merpass, it will also give you your latitude. The time of merpass coincides with the time when the sun is either directly north of you, or directly south of you. Table of merpass, taken from the daily pages of the Nautical Almanac available from ĭue to the rotation of the earth, the difference in time corresponds directly with your longitude. If you measure the precise time of merpass, you can compare that to the time of merpass on the Prime Meridian. Merpass is the meridian passage of the sun, which is the point at which the sun is at its highest point in the sky. Similarly, when you are on the equator, Polaris appears to have an altitude of 0°, matching your longitude.įor longitude, it is possible to use merpass. At that point, Polaris’s altitude is 90°, and your latitude is also 90°. It wobbles around a little bit, but generally, it will be directly overhead when you are at the north pole. You can find your latitude from Polaris, the North Star. Other celestial navigation techniques can be used to find either your latitude or your longitude, but not both. You transfer your first line of position using your course and speed in the same way you would with a terrestrial running fix. To complete a sun-run-sun, you need to take sights a couple of hours apart so that the angle between them is large enough to get an accurate fix. This is basically a running fix, using a celestial line of position from the sun as your position line. The other way of finding your position is to use the “sun-run-sun” technique. You can then work out your final position fix as the point where all your position lines intersect. 2000 Pub.Classic 6 star celestial position fix taken at sunrise or sunset.Įach sight gets plotted onto a chart, giving a line of position. He currently resides in Milford, Connecticut. He is also, frequent contributor to Cruising World magazine. About the Author: Hewitt Schlereth is an accomplished sailor who has written several books on navigation a including Commonsense Coastal Navigation and Latitude and Longitude by Noon Sight. The reader is taken carefully through several examples and situational illustrations, making this a most effective self-teaching guide. Schlereth demonstrates how to take sights by the sun, moon a stars and planets, discussing the advantages and disadvantages of each method. The basic process is simple: take, sight with sextant, establish, secondary reference or benchmark sight, compare the two sights and plot the result of the comparison on a chart. In this easy-to-use guide, Hewitt Schlereth explains clearly and concisely how to navigate any stretch of sea using only a hand-held sextant, watch, plotting sheet and a copy of the Nautical Almanac. And despite the proliferation of electronic navigational devices, celestial navigation remains an essential tool for those who do not wish to be caught short when modern technology fails. By Hewitt Schlereth, Practical considerations aside, there is something soul-satisfying about looking to the sky to plot one's course.
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