The Birth of Modern Astronomy

Text pp 617-620

• The development of modern astronomy began with a break from the philosophical views of the Greek astronomers and the religious views of the medieval Catholic Church.

We will begin by learning a bit about five very important scientists: Nicolaus Copernicus, Tycho Brahe, Johannes Kepler, Galileo and Sir Isaac Newton.

Nicolaus Copernicus (1473-1543)

• Nicolaus Copernicus lived in Poland and worked for the Catholic Church.

• He became convinced that Earth is a planet, just like the other five known planets.

• Copernicus held that Earth is a planet. He proposed a model of the solar system with the sun at the center.

• This was a major break from the ancient, geocentric view of the solar system.

Tycho Brahe (1546-1601)

• Tycho Brahe was a Danish noble born three years after Copernicus died.

• Brahe convinced the Danish king to give him an island and build him an astronomical observatory on it.

• Brahe’s observations, especially of Mars, were far more precise than any others made before him.

• (They were also considered to be very valuable by the King!)

Johannes Kepler (1571-1630)

• Johannes Kepler worked as Brahe’s assistant during Brahe’s last years, and was convinced of Brahe’s accuracy.

• Kepler used Brahe’s work to discover three important laws of planetary motion.

• 1. The path of each planet around the sun is an ellipse - an oval-shaped path - with the sun at one focus.

• 2. Each planet revolves so that the sun sweeps over equal areas in equal time intervals.

http://www.youtube.com/watch?v=M3-nQEyBHxg&feature=related

• 3. Solar distances of planets can be calculated when their periods of revolution are known.

Galileo Galilei (1564-1642)

• Galileo was the greatest Italian scientist of the Renaissance.

• His most important contributions were his descriptions of the behavior of moving objects.

Galileo and his Telescope • Galileo created his own telescope without

ever seeing one. Using it, he was able to view the universe in a new way.

• He made many important discoveries that supported Copernicus’s view of the universe…

1. The discovery of four satellites of Jupiter

• This proved that the old idea of the Earth being the only center of motion was wrong.

• Jupiter was another center of motion, too!

2. The discovery that planets are circular disks…

• … not just points of light. This showed that the planets must be Earth-like, so Earth wasn’t that special.

3. The discovery that the moon’s surface was not smooth.

• Galileo saw mountains, craters, and plains, very much like the ones on Earth.

4. The discovery that the sun had sunspots, or dark regions.

• Galileo tracked the movement of these spots and estimated the rotational period of the sun as just under a month.

Galileo’s Fate • The Roman Catholic Church tried to control

the work of scientists during Galileo’s time.

• In 1616, the Church condemned the Copernican theory and told Galileo to abandon it.

• Galileo refused and then wrote his most famous work. Critics pointed out that Galileo was promoting the Copernican view of the solar system.

• Galileo was called before the Inquisition. He was tried and convicted of heresy.

Sir Isaac Newton (1642-1727)

• Sir Isaac Newton was born in the year of Galileo’s death. Many scientists before him had attempted to explain the forces involved in planetary motion.

• While still a very young man, Newton described a force that extends from Earth into space and holds the moon in orbit around Earth.

This is the apple tree that Newton sat under when he watched an apple fall and speculated about the nature of its falling.

• Although others had theorized the existence of such a force, Newton was the first to formulate and test the law of universal gravitation.

Universal Gravitation

1. Every body in the universe attracts every other body, but this attraction depends upon the bodies’ masses and their distances.

2. The greater the mass of the object, the greater its gravitational force.

3. The greater the distance between two objects, the LESS their gravitational force.