Early Views about the Cosmos

Ancient Views of the Cosmos Myths, folklore and legends were used to explain what ancient people observed in the night sky: First Nations people – believed the night sky was a pattern on a great blanket overhead, which was held up by a spinning ‘world pole’ resting on the chest of a woman named Stone Ribs.

Inuit in the high Arctic – used a mitt to determine when seal pups would be born, by holding the mitt at arm’s length at the horizon.

Solstice – represents the shortest and longest periods of daylight Winter solstice – shortest period of daylight (Northern hemisphere – Dec. 21) ~ 7.5 hours Summer solstice – longest period of daylight (Northern hemisphere – June 21) ~ 17 hours

The Ancient Celts set up megaliths, in concentric circles, at Stonehenge to mark the winter and summer solstices; light would shine on or through certain stones depending on the time of day and year

Ancient African cultures set large rock pillars into patterns to predict the timing of the solstices as well.

Equinox – represents periods of equal day and night Autumnal equinox – occurs in the fall (Northern hemisphere – Sept. 22) Vernal equinox – occurs in the spring (Northern hemisphere – Mar. 21)

The Mayans of Central America built an enormous cylinder shaped tower, at Chichen Itza, to celebrate the two equinoxes.

The Ancient Egyptians built many pyramids and other monuments to align with the seasonal position of certain stars. Great Pyramid and Sphinx

Models of Planetary Motion Throughout time we have tried to explain the motion of the objects in the sky About 2000 years ago, Greek philosopher Aristotle proposed the geocentric model (Earth-centered)- that the earth was the center of the universe and everything rotated around it in circular orbits

Geocentric Model BUT…. Why did some of the planets appear to loop back opposite their usual movement? http://www.astro.utoronto.ca/~zhu/ast210/geocentric.html

Heliocentric Model In 1530, polish astronomer Nicholas Copernicus proposed that the Sun was the center of the universe (not the Earth) and the planets orbited around it. Evidence of model was supported by the invention of Galileo’s telescope

Helicoentric Model

Some of the motions still could not be accurately predicted…. WHY? Up until now it was thought that the planets rotated around the Sun in a circular pathway…BUT this was found not to be entirely true!

Mathematician Johannes Kepler added to the heliocentric model when he discovered that the motion of the planets could best be explained by their elliptical orbits! As a Planet orbits and reaches closest to the sun it tends to speed up a little. Why do you think this is?