Astronomy  Astronomy is the study of the planets and other objects in space.  The “Golden Age of Astronomy” occurred during 600 – 150 B.C. when the ancient Greeks used observations, instruments, and geometry and trigonometry to make the first discoveries of space.

Aristotle (384 – 322 B.C.)  determined that Earth was round based on the curved shadow left on the surface of the moon when Earth fell between the sun and the moon..

Models of the Solar System  Geocentric Model – The Greeks determined that the moon, the sun, and the known planets (Mercury, Venus, Mars, and Jupiter) orbited Earth.  Heliocentric Model – Aristarchus ( B.C.) was the first Greek to believe in a sun-centered universe.

 Ptolemaic System – Claudius Ptolemy 141 A.D. He used the geocentric model, but was the first to explain retrograde motion (the planets move eastward in the sky, appear to stop, move backwards, and then resume its eastward movement).

The Birth of Modern Astronomy  Nicolaus Copernicus ( ) – The first major astronomer to make advancements since Ptolemy. He was the first to determine that Earth is a planet and that the sun is the center of the universe.

 Tycho Brahe ( )  He convinced King Frederick II to build an observatory in Copenhagen. Here, Brahe invented measuring devices (telescopes had not yet been invented) and made the most accurate observations of several planets, especially Mars.

The Birth of Modern Astronomy  Johannes Kepler ( ) – Studied under Brahe and continued his work by using math to develop 3 laws of planetary motion.  The path of each planet around the sun is an ellipse.

Kepler’s 1st Law Of Planetary Motion Each planet moves in an ellipse rather than a circle Each planet moves in an ellipse rather than a circle –Perihelion-When a planet is closest to the sun –Aphelion-When a planet is at it’s furthest distance from the sun

Kepler’s 2nd Law Of Planetary Motion Kepler’s second law says that an imaginary line between the sun and a planet sweeps out equal amounts of area in equal amount of time Kepler’s second law says that an imaginary line between the sun and a planet sweeps out equal amounts of area in equal amount of time

Kepler’s 3rd Law Of Planetary Motion States that the planet’s orbital period squared is equal to its mean solar distance cubed: States that the planet’s orbital period squared is equal to its mean solar distance cubed: T 2 = d 3, where T = planet’s orbital period and d = solar distance Therefore, the solar distances of the planets can be calculated when their periods of revolution are known.

The Birth of Modern Astronomy (3)  Gallileo Galilei ( ) –first to use the telescope.  Found 4 satellites (moons) around Jupiter.  Realized planets are circular disks, not just points of light.  Venus has phases (just like our moon does).  The sun has sunspots (dark spots).

 The discovery of 4 satellites (moons) around Jupiter.  The discovery that planets are circular disks, not just points of light.  Venus has phases (just like our moon does).  The sun has sunspots (dark spots).

The Birth of Modern Astronomy  Sir Isaac Newton ( ) – developed the Law of Universal Gravitation.  The gravitational pull is a result of the mass of the object and the distance between 2 objects.