The Copernican Revolution

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Had two sets of astronomical tables: one based on Ptolemy’s theory and one based on Copernicus’.

He found that both tables’ predictions were off by days to a month.

He believed that much better tables could be constructed just by more accurate observations.

Tycho’s homemade instruments improved measurement precision from ten minutes of arc (which had held since Ptolemy) to less than one

Slide 15

Tycho Brahe

Tycho’s homemade instruments improved measurement precision from ten minutes of arc (which had held since Ptolemy) to less than one

Great Quadrant

Triangular sextant

Armillary Sphere

Slide 16

The skies change

Tycho observed 2 phenomena that showed the heavens DO change:

In November 1572, Tycho noticed a new star in the constellation Cassiopeia

Comet of 1577

Prior to this sighting, comets were thought to be atmospheric phenomena because of the immutability of the heavens

But neither the star nor the comet changed position as the observer moved, as expected for atmospheric phenomena

Slide 17

A new star

In November 1572, Tycho noticed a new star in the constellation Cassiopeia

He collected observations of the nova from all over Europe

It did not change position as the point of view changed (as the moon does), so the object must be very far away, as far as the stars themselves

This is in direct contradiction with the traditional doctrine that since the heavens are perfect, they must be immutable

Slide 18

Comet of 1577

Prior to this sighting, comets were thought to be atmospheric phenomena because of the immutability of the heavens

Tycho, among others, made measurements of its changing position

Like the nova of 1572, it’s position did not move relative to the observer

Over the next two generations the perfection of the heavens was abandoned, as were the crystalline spheres of which they were supposedly composed.

Slide 19

Johannes Kepler

Kepler succeeded Tycho as the Imperial mathematician (but at only 1/3 the salary of the nobleman)

Kepler worked for four years trying to derive the motions of Mars from Brahe’s observations

In the process, he discovered that the plane of the earth’s orbit and the plane of Mars’ (and eventually the other planets) passed through the sun

Suspecting the sun had a force over the planets, he investigated magnetism

While this is not true, it did lead him to the idea of elliptical orbits

“With reasoning derived from physical principles agreeing with experience, there is no figure left for the orbit of the planet except a perfect ellipse.”