How to Use the Stars to Find Your Way


Finding Longitude: Take a Guess
Star map of the Northern Hemisphere. Note Polaris (the North Star) at the center.
Star map of the Northern Hemisphere. Note Polaris (the North Star) at the center.
Jan Tyler/E+/Getty Images

Latitude can tell you how far north or south you are. With repeated measurements, it can confirm you're travelling in a straight line, not in circles. Latitude alone, however, can't tell you where you are on the planet. You need longitude as well.

Longitude is your distance (in degrees) east or west of the prime meridian, and finding it is a difficult proposition for celestial navigators. Calculating longitude requires knowing the Greenwich Mean Time (GMT), and you can't find that using the stars. You need a very accurate timekeeper called a chronometer. (At Greenwich, England, the prime meridian is 0 degrees. If you know, for instance, that it is 7 a.m. in Greenwich when it is noon where you are, then you know you are 75 degrees east of Greenwich -- multiplying 5 times 15 degrees. The Earth turns 15 degrees per hour or 360 degrees in 24 hours) [source: Nova].

Longitude-wise, what the celestial navigator can achieve is a very rough approximation of east/west progress. By tracking the position of an east/west-setting star at the exact same time every day (assuming you have a watch), you can get a rough idea of how far you've traveled east or west [source: Thaler].

Ideally, though, in the days of GPS, and countless mapping apps, you won't need that much luck. Unless you're stranded in a desert or your boat sinks in the open ocean after being struck by a whale, star-based navigation is more a curiosity than a way to accurately navigate the globe. For most modern navigators, mastering the technique is primarily a path to a deeper understanding of the universe, the relationships between celestial bodies, and the relationship between those celestial bodies and you.

Author's Note: How to Use the Stars to Find Your Way

While in most cases, star navigation is more a hobby than a tool in modern times, I learned in the course of my research something at once reassuring and a little alarming: Even now, your airplane pilot and cruise-ship navigator learn the art. Should their instruments fail, they can find their way the old-fashioned way. Good to know they have a back-up. Frightening to know they might have to use it.

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Sources

  • Beyond the Map. "Octants, Quadrants, and Sextants." (April 15, 2013) http://www.beyondthemap.ca/english/ship_octant.html
  • Blue Planet Biomes. "Sonoran Desert." (April 17, 2013) http://www.blueplanetbiomes.org
  • Devlin, Keith. "Those Amazing Animal Mathematicians." Mathematical Association of America. October 1999. (April 8, 2013) http://www.maa.org/devlin/devlin_10_99.html
  • Gooley, Tristan. "The Future of Celestial Navigation." The Natural Navigator. (April 8, 2013) http://www.naturalnavigator.com/the-library/articles/celestial-navigation/
  • Gooley, Tristan. "How to Find Your Way Using the Stars." The Natural Navigator. (April 8, 2013) http://www.naturalnavigator.com/the-library/articles/how-to-find-your-way-using-the-stars/
  • Jones, Robert F. "Steven Callahan." People. March 28, 1983. (April 13, 2013) http://www.people.com/people/archive/article/0,,20084604,00.html
  • KirchdorferWeb Astronomy. "Measuring the Night Sky." (April 11, 2013) http://www.kirchdorferweb.com/astronomy/beginner1.html
  • National Geographic Education. "Navigation." (April 12, 2013) http://education.nationalgeographic.com/education/encyclopedia/navigation/?ar_a=1
  • Nature Skills. "Navigation without a Compass." March 26, 2009. (April 11, 2013) http://www.natureskills.com/survival/land-navigation/
  • NPR - Talk of the Nation. "Stories of GPS Directions Gone Wrong." Aug. 12, 2009. (April 12, 2013) http://www.npr.org/templates/story/story.php?storyId=111809897
  • The Old Farmer's Almanac for Kids, Volume 1. "Find Your Way Without a Compass." (April 8, 2013) http://www.almanac.com/content/find-your-way-without-compass
  • Ordnance Survey Magazine. "Navigating using the sun, moon and stars." (April 10, 2013) http://www.magazine.ordnancesurveyleisure.co.uk/magazine/tscontent/editorials/outdoor-skills/map-and-navigation-skills/sun-moon-and-stars.html
  • Rao, Joe. "The Big Dipper and the Cross." Space. May 12, 2006. (April 12, 2013) http://www.space.com/2400-big-dipper-cross.html
  • Rao, Joe. "Navigating By the Stars." Space. Sept. 19, 2008. (April 10, 2013) http://www.space.com/5849-navigating-stars.html
  • Science By Email. "Try this: Finding South." (April 12, 2013) http://www.csiro.au/helix/sciencemail/activities/crux.html
  • The Science Notebook. "Astronomy – Exploring the Night Sky: Finding Altitude." (April 11, 2013) http://science-notebook.com/astronomy01.html#Determining_Altitude
  • Sloan Digital Sky Survey. "Mapping the Sky." (April 14, 2013) http://cas.sdss.org/dr7/en/astro/mapsky/mapping_the_sky.asp
  • Smith, Mike. "Comparing the sky from different latitudes." Star Attractions Column. North Museum of Natural History and Science. Sept. 1, 2012. (April 11, 2013) http://www.northmuseum.org/Portals/0/planetarium/cosmic%20mike/Star%20Attractions%20Column%20-%20Sept%201%202012.pdf
  • Te Ara Encyclopedia of New Zealand. "Story: Southern Cross." (April 11, 2013) http://www.teara.govt.nz/en/southern-cross/page-1
  • Thaler, Andrew David. "Sailing by Starlight: The lost art of celestial navigation." Southern Fried Science. Sept. 27, 2010. (April 10, 2013) http://www.southernfriedscience.com/?p=7827
  • Wilderness Survival Skills. "Navigate by the Southern Cross." (April 10, 2013) http://www.wilderness-survival-skills.com/southern-cross.html
  • VanHaren, Amy. "Celestial Navigation." Appalachian Mountain Club/AMC Outdoors. Jan/Feb 2013. (April 8, 2013) http://www.outdoors.org/publications/outdoors/2013/learnhow/tips-for-celestial-navigation.cfm

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