Early Models of the Universe

heliocentric

sun centered model

first proposed by Aristarchus

Nicholas Copernicus revisited

geocentric

model where the earth is at the center of the solar system

first proposed by Aristotle

Ptolemy used this model

epicycle

small circle that a planet each planet was thought to move around while also moving around the earth

retrograde motion

when a planet seems to be going in backward loops in the sky

prograde motion

when a planet seems to move forward across the sky

ptolemaic model

placed earth at the center (geocentric)

epicycles

sun, moon, planets revolve around earth

used circular orbits

copernican model

sun is the center (heliocentric)

earth and planets revolve around the sun

circular orbits

retrograde motion was result of Earth “overtaking” a planet in its orbit around the Sun

galilean satellites discovered…

orbits of jupiter’s moon

moon like phases

sunspots

craters on the moon

galileo’s proof that supported heliocentric model

jupiter’s moon orbits proved that not everything revolves around earth

summarize the experiment that Eratosthenes conducted which determined the circumference of the Earth

he compared the sun’s shadows in 2 egyptian cities, syene and alexandria the sun cast no shadow in syene but it did in alexandria, he measured the angles of the shadow and used the distance between the cities to calculate earth’s circumference

focus

each point at which the string is pinned

eccentricity

measure of how flattened an ellipse is

semimajor axis

half the length of the major axis

orbital period

time needed for the planet to complete 1 circuit around the sun

force

push or pull

mass

the total amount of matter the object contains

acceleration

the rate of change of the velocity of an object speeding up, slowing down, or simple changing direction

gravitational force

force of attraction between objects with mass

inertia

the tendency of an object to keep moving at the same speed and in the same direction unless acted upon this

Kepler’s three laws

1. orbital paths of the planets are elliptical

2. an imaginary line connecting the sun to any planet sweeps our equal areas of the ellipse in equal intervals

3. the square of a planets orbital period is proportional to the cube of its semimajor axis

Newton’s Laws

1. every body continues in a state of rest or in a state of uniform motion in a straight line unless compelled to change by a force

2. when a force acts on a body of mass it produces in it acceleration equal to the force divided by the mass

3. to every actions there’s an equal and opposite reaction

law of universal gravitation

every object in the universe attracts every other object with a gravitational force