Lecture notes:

• We live on the surface of a sphere of rock, the third planet from SOL, 70% of its surface covered by blue—green oceans and swept by swirling patterns of clouds. The first measurement of its size was made by Eratosthenes of Alexandria near 273BC. He noted that sun never fully reaches the bottom of a well in Alexandria on summer solstice (June 21). By measuring the dimensions of the well (50 ft deep and 6.4 feet in shadow he could have measured an angle of 7.3 degrees, for the distance of the sun at summer solstice from the zenith. Eratosthenes learned that at Aswan, 811 km to the south, sunlight actually reached the bottom of a similar well. He concluded that the difference was due to the spherical shape of the earth and developed the proportion: 7.3 degrees/360 degrees = distance (Aswan to Alexandria/Circumference of earth. From this proportion he could have established the circumference of the earth to be 40,000 km or 24,000 miles; the diameter of the earth would be the circumference divided by pi and equal to 12,732 km.

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• For centuries upon centuries, the spherical earth was believed to be in the center of a geocentric universe. The Copernican revolution which culminated in the ideas of gravity developed by Isaac Newton after he was hit on the head by an apple in 1667, finally moved the earth from the center to the moving third planet. That heliocentric universe lasted until 1920 when Harlow Shapley at Mt. Wilson Observatory near Los Angeles showed that out sun was 30,000 light years away from the center of the galaxy. Now we realize that even our galaxy is not in the center, but it revolves around another large cluster of galaxies sever hundred million light years away. We have no right, therefore, to think that we are special creatures because we live in the center of the universe, or, in facts, that we live in any unique or special part of the universe. We are peripheral creatures on a planet orbiting an ordinary star when orbits an ordinary galaxy. In our universe of curved space and curved time, there is no center; or as the poet would say the center is everywhere.

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• The universe is expanding, having emerged from a BIG BANG some 12-15 billion years ago. Before that BIG BANG all was darkness, ignorance, and chaos.