Astronomy 8/26

astronomy

scientific study of space and universe

astrology

belief that celestial positions affect human behavior

heliocentrism

Sun at center of solar system

geocentrism

Earth at center of universe

retrograde motion

planets appear to move backward

absolute motion

actual movement in space

apparent motion

how movement looks from Earth

AU

distance Earth-Sun (~150,000,000 km)

Aristotle

geocentrism; perfect spheres

Ptolemy

geocentrism with epicycles

Copernicus

heliocentric model

Galileo

telescope evidence (Jupiter’s moons, Venus’s phases)

Tycho Brahe

accurate naked eye observations

Kepler

3 laws of planetary motion. Noticed speed of planets changing. Brahe’s assistant

Newton

gravity explains orbits

Kepler 1st law

Planets travel in elliptical orbit with the sun at one focus

Kepler 2nd law

A line joining a planet and the sun sweeps out equal intervals of time (known as the equal area law)

Kepler 3rd law

There is a direct relationship between a planet’s period & it’s average distance from the sun.

(P^2 = a^3)

Kepler 3rd law example

4 AU -> P = 8 years

Charles Messier

Was interested in strange fuzzy objects

William Herschell

first to discover infrared lights. Discovered Uranus.

Urbain LeVaerrier

Discovered Neptune by doing math

Albert Einstien

introduced SpaceTime

Edwin Hubble

Discovered that the universe is expanding.