History of Early Navigation before 1492 AD Montgomery College Planetarium at Takoma Park/Silver Spring By Dr. Harold Williams

Problem How to get home after hunting to the wife and kids bring the meat home. How do you get home after fishing from your boat. How do you get to that island or town or city on the coast to trade and then get back home.

People still have to solve this problem

Now

EgyptianEgyptian trading Egyptian ship, 1250 B.C. Egyptian ship on the Red Sea, showing a rope truss being used to stiffen the beam of this ship Stern-mounted steering oar of an Egyptian riverboat depicted in the Tomb of Menna (c B.C.)Menna

PhoenicianPhoenician Glass

China Trading /wiki/Junk_(ship) /wiki/Junk_(ship) /wiki/Zheng_Hehttp://en.wikipedia.org /wiki/Zheng_He

Arab Trading

Data, the sky, Sun first! Regularity in day light and dark at night. Changes is length of day light and dark at night, duration. Changes in the position of sunrise and sunset. Changes in the length of shadows at noon time through out the year. The shortest shadow of the day is always at noon time local apparent solar time.

We can recognize solstices and equinoxes by Sun’s path across sky: Summer solstice: Highest path, rise and set at most extreme north of due east. Winter solstice: Lowest path, rise and set at most extreme south of due east. Equinoxes: Sun rises precisely due east and sets precisely due west.

Sun’s altitude also changes with seasons Sun’s position at noon in summer: higher altitude means more direct sunlight. Sun’s position at noon in winter: lower altitude means less direct sunlight.

Data, the sky, Moon second! Regularity in moon light, changing phases. Changes is moon rise with phases. Changes in moon transit with phases. Changes in moon rise with phases.

Phases of Moon Half of Moon is illuminated by Sun and half is dark We see a changing combination of the bright and dark faces as Moon orbits

Moon, anti-Sun Does appear in day time, too. But phases and moon rise, moon transit, and moon set have a one to one correlation.

Now we have some time clocks and some directions South line with shortest shadow of the day. Four cardinal point, 1.) South; 2.) Anti-South, North (where the sun and moon and planets never are); 3.) Eastward (where the sun comes up, but it moves around with the yearly seasons); 4.) Anti-Eastward, Westward (where the sun goes down, but it move around with the yearly seasons) For day light when the Sun, Helos, Sol rules.

Cardinal Directions Azimuth

Latitude

Thought Question What is the arrow pointing to? A. the zenith B. the north celestial pole C. the celestial equator

Cross Staff

Longitude