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Celestial Navagation

Updated: Feb 14, 2020

By Hannah Pan

Image by Tim Prudente for Capital Gazette

For hundreds of years, people have looked to the stars as a guide to find their way around the world. The heavens were relied upon when technology and navigational tools were very simplistic. Yet even today, with advanced satellites and Global Positioning System (GPS), sailors and other navigators use the skies as a guide. Let’s explore the history of celestial navigation, the practice of using the stars, sun, and moon to find one’s way.

Even before the 1400s, celestial navigation was utilized by Pacific Islanders, Persians, and Arabs.1 These people depended upon the stars as landmarks in the sky when sailing. They each came up with different ways to remember the locations of these stars. For example, the Arabs used poems to remember the stars’ positions, while Polynesians drew visual images through the stars by connecting the bright dots in the sky to outline fish and other animals. In addition, Polynesians used the stars’ locations to create more advanced navigational tools, such as the star compass.

A few hundred years later, in 1895, a Canadian seaman named Joshua Slocum embarked on a journey that lasted for three years. He became the first man to single-handedly sail around the world. At this time, there were still no advanced navigational tools, and Slocum had to depend on celestial navigation, specifically a technique known as the “lunar distance method”, which involves measuring angles between the moon and stars to determine one’s longitude.

Celestial navigation usually involves measuring angles between a known celestial body and the horizon. A sextant is used to measure these angles. This tool consists of a telescope attached with a circular arc marked with degrees. The navigator looks through the telescope of the sextant, aligns it with the horizon, and uses the circular arc to measure the angle to the star. These measurements, combined with the chronometer’s measurement of the time of day, are then compared against an almanac. The almanac contains published tables of measurements from which the navigator’s latitude can be determined.

While this method of navigation may seem outdated, it was part of the required U.S. Naval Academy curriculum since 1845 until 1998. Before 1998, Navy members were required to know how to use a sextant and perform the tedious mathematical calculations involved in celestial navigation. Modern navigators and sailors no longer need to know how to use such tools, since computers and advanced technology can easily and more accurately determine a ship’s location now. However, due to today’s threat of possible cyber attacks, celestial navigation was reinstated at the Naval Academy in 2015. Since sextants are completely mechanical tools, they cannot be hacked like satellites and GPS.

Although celestial navigation relies on tools invented long ago, it is a tried and true method that has guided numerous sailors and adventurers for hundreds of year and still continues to do so today.


1. https://www.ruf.rice.edu/~feegi/astro.html

2. https://www.britannica.com/biography/Joshua-Slocum

3. https://onlinelibrary.wiley.com/doi/abs/10.1002/j.2161-4296.1997.tb01934.x

4. https://www.rmg.co.uk/discover/behind-the-scenes/blog/time-solve-longitude-lunar-distance-method

5. https://www.britannica.com/technology/sextant-instrument

6. https://www.britannica.com/science/celestial-navigation

7. https://www.nytimes.com/1998/05/29/us/c-navy-cadets-won-t-discard-their-sextants-169919.html?n=Top/Reference/TimesTopics/Organizations/U/United+States+Naval+Academy

8. http://www.capitalgazette.com/news/ph-ac-cn-celestial-navigation-1014-20151009-story.html

Editor: Jo Ann Sun

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