SUMMERY OF ASTRONOMY

ARISTOTLE

• Greek philosopher
• Thought the Earth was the center of all things
• Realized when the Earth moves, the star's position would change
• Used the Geocentric model
• 384-322 BCE

ARISTARCHUS

• 310-230 BCE
• Greek astronomer and mathematician
• Used the Heliocentric model
• Attempted to measure distances to the sun and moon.
• Ratio was too small

PTOLEMY

• 100-170 CE
• Lived in Alexandria, Egypt
• Wrote the " Almagest"
• Created. The Wheels on wheels system

NICOLAUS COPERNICUS

• 1473-1543
• Felt ptolemy's model was too complicated
• Also used a wheels on wheels system
• His Heliocentric model is seen as the first step of modern models

JOHANNES KEPLER

• 1571-1630
• German mathematician and astronomer
• Did not believe planets to circle perfectly
• Formed three principles (Kepler's Laws)

GALILEO GALILEI

• 1564-1642
• Used scientific methods
• Added improvements to the telescope
• Observed the moons, Io, Europa, Callisto and Ganymade. (Jupiter)
• Observed that Earth was not the only thing orbited

ISAAC NEWTON

• 1642-1727
• First scientist to describe gravity scientifically
• Formulated the "Law of universal gravitation"

EDWIN HUBBLE

• 1889-1953
• played a crucial role in establishing extragalactic astronomy
• Proved "nebulae" were actually galaxies beyond the Milky Way.
• Practiced armature boxing

GEOCENTRIC MODEL

• Places the Earth at the center of the universe

HELIOCENTRIC MODEL

• Places the Sun at the center of the universe

Kepler's first law:
Elliptical Orbits- planets orbit in a eclipse with the sun at one focus.

Kepler's second law:
Equal Areas, Equal Times: planets sweep out equal areas at equal times.
-at perihelion , the planets is moving faster
-at aphelion, planets is moving slower

Kepler's third law:
Length of Orbit/Distance from the Sun: the is a mathematical relationship to planets period of revolution and it's distance from the sun.

LAW OF UNIVERSAL GRAVITATION

• The force of gravity:
• Increases as the masses of the object increase
• Decreases as the distance between the objects increases

Centripetal Force = planet's orbit

• The sun's gravity is the force that keeps the planet in orbit