Celestial navigation, also known as astronavigation, refers to the ancient and modern practice of position fixing that enables a navigator to transition through a space without having to rely on estimated calculations, or dead reckoning, to know their position. It involves the use of the stars, sun, moon, and other celestial bodies as visible reference points that are used to calculate an observer's position in terms of latitude and longitude on the Earth's surface. Crucial tools used in celestial navigation aboard a ship include the sextant, chronometer, and compass. A sextant is an optical instrument used to measure the angle between any two visible objects, which aids in determining the navigator's latitude. The chronometer, an extremely accurate timepiece, is an essential tool for calculating longitude. The compass guides navigators in determining direction relative to geographical cardinal directions. Furthermore, published tables containing data about the predicted positions of celestial bodies at various times, such as nautical almanacs, were traditionally also used in this method of navigation. By correlating the observations made through these instruments with the information in these tables, seafarers could accurately determine their location on the globe. Celestial navigation served as the primary method of navigation until the latter part of the 20th century, when electronic global positioning systems such as LORAN (Long Range Navigation) and GPS (Global Positioning System) started to be developed and utilized. These systems revolutionized navigation by providing real-time, accurate positions, making the process substantially easier and more efficient. Despite this, the knowledge and ability to perform celestial navigation remains a vital skill, acting as a backup in case electronic systems fail or are unavailable.

1. Explorers during the Age of Discovery utilized celestial navigation to traverse the open oceans. They relied upon the positions of stars, along with rudimentary instruments like astrolabes, to help guide them on their journeys to unfamiliar lands. 2. A sailor at sea under a clear night sky uses a sextant to determine the angle between a known star and the horizon. This information, along with a current time measurement from a chronometer and previously published tables of star positions, helps the sailor determine their latitude and longitude, thereby pinpointing their location in the ocean. 3. During World War II, naval and air forces used celestial navigation in the absence of modern GPS technology. They employed tools like bubble sextants, which allow for more accurate measurements from moving vehicles, in conjunction with the position of the moon, planets or stars to guide them to their intended destinations. 4. In the mid of 18th century, the invention of marine chronometer by John Harrison revolutionized celestial navigation by providing precise timekeeping, thus enabling navigators to accurately calculate longitude. This significantly increased the safety and efficiency of long sea voyages. 5. The Polynesians used celestial navigation to traverse vast expanses of the Pacific Ocean. They developed an extensive system based on observing the stars, the movement of clouds and birds, and the direction of the wind and waves. Using these natural signs along with detailed mental maps, they were able to navigate with exceptional accuracy across thousands of miles of open sea.

Fun Fact: Celestial navigation includes a technique known as "shooting the sun"! This does not mean you shoot the sun with a weapon, but rather with a sextant - an instrument used to measure the angle between a celestial object and the horizon. "Shooting the sun" typically happens at noon when the sun is at its highest point in the sky above the horizon. This height is called the sun's meridian altitude, which changes throughout the year due to Earth's tilt and is different for every particular point on the planet. By comparing this measured angle with the standard tables indicating the sun's position for any given time and date, navigators could accurately establish their latitude. The process, though sounding simple, required significant skill and experience, as waves and motion of the ship could greatly affect the accuracy of the reading. Until today, celestial navigation remains an essential backup for electronic systems and a part of maritime education and tradition.