Friday, January 15, 2016

Navigation by the Stars

Since the beginning of time, people have traveled to new places, both by sea and land. Modern GPS uses man-made satellites launched into space to aid navigators, but long before these machines, or even the simple compass, travelers have used the natural satellites in the heavens: the stars. Explorers took advantage of the stars’ unwavering presence and patterns to guide them on their journeys.

There are many ways that stars helped the early sailors before modern sailing technology. They were used to help many early sailors navigate the seas during the night. Without having a way to actively maintain their course after the sunset, ships would have been blown off course, never made it to their destinations, and never make it back to their home port. Sailors used the stars to determine their latitude. Sailors in the northern hemisphere could use the North Star to “anchor” their direction, or use the Southern Cross (Crux) constellation in the southern hemisphere.  By placing these celestial pole-markers in front or behind them, the navigators knew which direction they were going.

Polaris, also known as the North Star, is part of the
Ursa Minor constellation, more commonly called the "Little Dipper"
Did you know that the name “Polaris,” used for the North Star, is not actually the name of this guiding star? Astronomers have found that as the earth moves, a different star can come into prominence as the north pole star. Before the current “Polaris” ascended to its position, it used to be called Phoenix. Scientists believe that eventually the star Vega will become the most prominent northern star.

The stars and constellations functioned as a calendar and clock as well. The stars and constellations were first named by early Greek and Roman astronomers. A constellation is a group of stars forming a recognizable pattern that is traditionally named after its apparent form or identified with a mythological figure. They discovered that while some constellations (Ursa Major and Minor, Cassiopeia, and Cygnus) could be see nearly every night, others were only seen seasonally, or in different places depending on the season. Astronomers recording the time and location of constellations created star maps. It certainly helped that the Roman Empire was so far-reaching; it meant there were wide variations in latitude. A map from one location could be checked against another to help sailors navigate north and south. During the day, the angle of the sun was used as a clock. At night the Big Dipper’s positioning was used as a 24 hour clock to tell time. By using these positions, navigators would be able to determine if they were traveling east or west.

Cygnus - the Swan. 
If you look carefully, you can imagine the neck extending up to the left,
and the stars that form his body and tail in the lower right.
When we think about navigation by the stars, we think of ships on the open seas, with no landmarks to help them. But what about traveling across unfamiliar land? One couldn’t write “Turn left at the third tree,” and be sure that the directions would remain accurate! Were the sun and stars also used for land travel? Of course. By using the same navigational principles, travelers could cross overland. The sun was used during the day on land to determine direction during travel, and stars would re-orient their paths at night.  When there was enough moonlight for the travelers to see any obstacles on the ground, they could also use the stars to travel at night. Using the constellations was how escaped slaves slipped through the darkness to freedom.  They would follow the "Drinking Gourd," their name for the Big Dipper, knowing that its handle never wavered in pointing them towards the right direction.

Perhaps the most famous single "star" used for overland, overnight travel is the one that brought the three Magi to Bethlehem. However, modern astronomy has disproved that the Star of Bethlehem was just any star. In fact, it probably wasn’t even a star at all! Based on the history of the Roman Empire and the census that called Mary and Joseph to Bethlehem, the location of the city, and patterns seen since, the “Star of Bethlehem” was likely either a comet called Kepler, a supernova (exploding star), or a planetary abnormality and/or alignment. 

Star and constellations were used for navigation in many ways. They were used by sailors to be able to tell the location of their ships and the direction to travel in. The were also used as a calendar and a clock. Overland travel was aided by the position of the sun and stars as well. As long as the navigators could see the stars, they could travel. May you always have clear skies and smooth sailing!

Photo note: We took these pictures of the stars in "real time" using the Skyview: Explore the Universe App.  It's pretty cool for navigating the backyard in modern times, or even just amateur star gazing.  Plus, it shows celestial bodies' regardless of where you are.  By aiming the camera south and through the floor, we were able to "see" the location of Crux through the earth!  When we took this photo, Mercury, Saturn, and Scorpio were not visible outside due to placement and daylight, but we were able to "find" them in our kitchen.

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