Know about Copernicus and the Sun-Centered Model

Know Kepler’s Laws of Planetary Motion

Astronomy and the Renaissance

Ptolemy’s ModelClaudius Ptolemy – AD 150

Ptolemy believed that heavenly bodies (planets and stars) were perfect, in contrast to earthbound objects

For 1,300 years, his model was the conventional wisdom of the scientific world

The universe was based on perfect circles

An epicycle is the circular orbit of a planet, the center of which revolves around the Earth in another circle

Lesson Overview Copernicus and the Sun-Centered Model Kepler’s Laws of Planetary Motion

Copernicus and the Sun-Centered Model

Why Copernicus Searched for a Better Model

Ptolemy’s model designed to predict planetary movements were off (by as much as 2 degrees)…

Hence calendars, largely based on astronomical bodies were not accurate. More accurate data was needed for the Roman Catholic Church in order to correctly observe religious events.

In addition, Ptolemy’s theory of epicycles didn’t adequately explain changes in Mars’ brightness

Copernicus’ Heliocentric SystemEarth, one of several planets revolving around the SunPlane of Earth’s equator tiltedMoon revolves around EarthEarth’s atmosphere simply follows Earth as it rotates

Tycho Brahe’s (1571-1630)Danish astronomer and fierce

mathematician Tycho’s observations didn’t confirm the

more recent Copernican model.Trying to bridge the two Tycho

developed a hybrid model that put Earth at the center of Sun’s orbit Other planets orbiting Sun

Wrong conclusion for a good reason

Tycho Brahe

Tycho Brahe's contributions to astronomy were atill enormous.

Supernova (1572) He not only designed and built

instruments, he also calibrated them and checked their accuracy periodically….thus he revolutionized astronomical instrumentation.

He also gave a young mathematician, Johannes Kepler a break…..well sort of

Tycho Brahe

Kepler’s First Law: The Significance of the Ellipse

Ellipse – a geometrical shape of which every point is same total distance from two fixed points

Each planet’s path around the Sun is an ellipse

The Sun is at one focal point

Kepler’s Second Law: The Planets’ Changing Speeds

A planet speeds up when it is closer to the Sun, and slows down when it is farther away

How Kepler’s Third Law Implied the Force of Gravity

Kepler hypothesized that a force held the planets near the Sun—gravity

His 3rd Law states that the square of a planet's orbital period is proportional to the cube of its average distance from the Sun. (period)2 = (constant) x (average distance)3

Harmonic Law: expresses a relationship between the time a planet takes to orbit the Sun and its distance from the Sun

Longer distance from sun, longer time to orbit, more distance traveled thus slower speed in its orbit

Extra Credit: This Saturday

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Know about Copernicus and the Sun-Centered Model

Know Kepler’s Laws of Planetary Motion

Astronomy and the Renaissance

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