Celestial Sphere

What is this? It looks like the inside of a seashell or a Fibbonacci sequence, but it's the dome of San Francisco's new shopping centre. It was preserved from the department store that once occupied the site.

By 240 BC, many educated people believed that Earth was spherical. In that year Erastothenes, librarian of Alexandria, made a remarkable estimate of Earth's size. Making use of Pythagorean geometry, Erastothenes combined the Sun's altitude at different locations with estimates of the distance to those locations. He derived a circumference of 250,000 stadia. Though the exact length of a Greek "stadium" is unknown, Erastothenes' estimate was amazingly accurate.

Aristarchus of Samos, a later librarian of Alexandria, published two books about the universe. His work "On the Sizes and Distances of the Sun and Moon" contained estimates that were strikingly good for their time. Those distances were measured from the Earth, fitting an Earth-centred cosmology. The enormous distances to solar system objects may have started Aristarchus thinking about alternatives. He published another book that is now lost and known only through citations of contemporaries like Archimedes.

This second book introduced a cosmology with the Sun in the centre and Earth circling as a planet. Aristarchus also believed that the stars were immeasurably distant, to explain their lack of parallax. This second book caused great argument. Another contemporary wrote that Aristarchus should have been put on trial for impiety! The cosmology of Aristarchus was incredibly prescient for its time, and the reaction to it predated that given to Galileo and Bruno. (Did Aristarchus get nasty comments on his blog?)

In discussions online and at conferences, I have observed that "standard model" cosmology is in big trouble. It has harmed the reputation of science. Most people doubt the existence of "dark energies," and are waiting to hear alternatives. Once the initial barrier of resistance is broken through, there is a ready audience for better Theories.