Constellations for Navigation: Past History
The Minoans of Crete (around 2000-1400 BC) used navigation of the stars to travel between lands over open water, during night. Homer’s Odyssey, depicting Calypso advising regarding Ursa Major, indicates evidence of the constellations being used for navigation (around 800 BC). Different constellations were identified and used at perhaps different times in history, building upon prior discoveries in some cases. For example, evidence of Ursa Minor (Little Bear) did not appear till 300 BC. More challenging voyages, e.g. from Greece to Britain, were accomplished by knowledgeable and capable navigators such as Pytheas. In addition to the stars above, the sediment underneath was sampled to aid navigation, as well as a “sounding bell” to understand depth by frequency change. Other tools used for navigation, in addition to the stars and depths, were the monsoon winds (e.g. from India) which allowed voyages in the Indian Ocean and South China sea, typically twice a year.
The magnetic compass complemented navigation by stars, after development between 1040 and 1117 AD in China. Such invention allowed navigation when the stars were not visible, and eventually allowed trans-ocean voyages. Portugal and Spain led many innovations and documentation of sailing, which paved subsequent discovery of the New World. Invention of the marine chronometer in 1700s and the sextant in 1757 allowed greater navigation precision; thereafter, radios and other discoveries led to further improvement in farther and more precise navigation.
Navigation using the stars, with all its attendant history, has important implications for even today. A sailor who has somehow lost all electronic and magnetic communication can still utilize the stars at night to navigate in an otherwise impossible setting. While many more than the initial 58 or so stars have been discovered, named, and can potentially be used for navigation today, the sights are set beyond earth (as covered in the Future section).
Constellations for Navigation: Present Status
To the person looking at the stars today (overcoming the bright lights of the big or moderate cities, on a clear-enough night, with great patience, and avoiding the temptations of using a GPS instead), the “big five constellations” for navigation are Cassiopeia, Crux, Orion, and the Big and Little Dipper.
The location of the North Star (within 1 degree of true north) is found by “pretending one is pouring from the Big Dipper’s ladle, and the flow points to North Star (without going too far into a “W” shape which is Cassiopeia.
Either the intersection of the line connecting the points of the crescent moon to the horizon points due South (or so does Orion’s sword, which may be more difficult to find).
In the Southern hemisphere, the North Star is not visible, but the constellation “Crux” resembling a kite (which, when a line is drawn between top and bottom of the kite, points South).
The “stick test,” paraphrasing advice from Mental Floss, allows determination of whether one is facing north, south, east, or west… by placing two sticks parallel with a star between these, subsequent movement of the star to the left suggests the sticks point north, to the right suggest south, rising suggest east, and lowering suggest west.
Constellations for Navigation: Future
The ability of satellites in space have allowed pin-point accuracy to within 10 feet (and in some cases, perhaps more), independent of visibility (obscured by clouds, fog, etc.). However, looking beyond the earth, for space travel, the constellations still have significant impact as a tool for navigation.
Beyond landing on the moon, the more recent successes of missions to Mars and even more uniquely landing a spacecraft on a comet have all relied upon such navigation, as well as other techniques.
Rosetta, part of the European Space Agency’s mission, orbited the comet and accomplished a landing on the comet.
Here, beyond the “constellations” as a whole, the sole star of the sun in inter-planetary travel is critical. For example, knowledge of orbits of the planets in relation to the single star of the sun can allow more efficient traversal.
Hence, the idea of “navigation by constellations” is not outdated, but likely to undergo a far more technical rejuvenation as space travel, including to Mars and beyond, becomes more of an emphasis – use of delta-v (change in speed from one orbit to another), aided by taking advantages of certain forces (including the slingshot effect, further saving energy – all to be addressed in a future article), rely upon the “constellations” and their inherent physical forces.