Origin of Modern Astronomy

Key Terms

1. Astronomy – It is the science that studies the universe. It includes the observation and interpretation of celestial (spatial) bodies and phenomena.2. Geocentric Theory - Earth centric Universe3.Heliocentric Theory – Sun centric Universe4. Gravity - the force that attracts a body toward the center of the earth, or toward any other physical body having mass.

5. Inertia – The tendency of an object to resist a change in motion. 6. Observatory – A building that contains one or more telescopes.

Geocentric Theory

Ancient Greece

Geocentric Model: Ptolemy (87-150 AD) Used epicycles to explain planetary movements

The Birth of Modern Astronomy

Copernicus - 1473-1543

Suggested a model that the Sun was the center of the universe.

This model explained the retrograde motion of planets better than the geocentric model.

Heliocentric Theory

The Birth of Modern Astronomy

Tycho Brahe

Johannes Kepler

Tycho Brahe - 1546-1601 the greatest of the pre-telescope observers in Europe.

His measurements about the , positions of Sun, Moon and planets, especially of Mars, were far more precise than any made previously.

• Kepler was an assistant to Tycho Brahe. • He used Brahe’s observations to study the orbit of Mars• Discovered three laws of planetary motion: predict with

accuracy the motions of the planets.

Johannes Kepler - 1609

first scientist to use a telescope to observe the sky.

observed the phases of Venus and the moons of Jupiter. Both observations supported the heliocentric model.

Galileo - 1564-1642

Sir Isaac Newton – 1642-1727

English scientist

explained gravity as the force that holds planets in orbit around the Sun.

Gravity’s Influence on Orbits

Gravity

• Gravity is the force that– holds us to the Earth– causes a rock to fall towards the ground– causes the Earth to go around the Sun– causes the Sun to be pulled towards the center of the

Milky Way galaxy

• Gravity acts between any two objects even if they are far apart. – “action at a distanceaction at a distance”

Modern Universe

Is the Sun the center of the Universe?

Final Question

• Final Question