Astronomers Unit 1

Kepler 1st Law

The orbits of the planets are *ellipses* with the Sun at one focus.

Kepler 2nd Law

The line joining the Sun and the planet sweeps out equal areas in equal times.

Kepler 3rd Law

The square of a planet's orbital period is proportional to the cube of the semi-major axis of its orbit.

P2 is proportional to A3 (P=period, A=distance or semi-major axis)

Galileo & the telescope

Did not invent the telescope, greatly improved Hans Lippershey’s toy model

* discovered the moons of Jupiter w it

Galileo & inertia

Was the first to correctly define the laws of inertia (an object at rest remains at rest, an object in motion will stay in motion)

Copernicus’s views

* Proposed heliocentric model
* earth rotates on axis once/24hrs
* Retrograde motion is the cause of earth “passing” superior planets, making them appear to move backwards in regard to outward stars.
* Infinite universe

Tycho’s (Brahe) contributions

* positions of planets
* Planets revolved around the sun, but the sun revolved around the earth
* Stella nova = super nova
* enabled Kepler’s 3 laws of planetary motion

Arcminutes (Tycho)

1/60th degree, moon 30 arcminutes across

Ptolemy

* Retrograde explained by deferents, eccentrics, and epicycles
* each planet moved in a small circle (epicycle), which in turn moves along a larger circle (deferent). Planets motions are centered on a point (eccentric)
* Geocentric
* Wrote the Almagest

Kepler & arcminutes

Orbit of mars was different from a circle by 8 arcminutes, showed that the orbit of mars was an ellipse

Thales

emphasized metaphysics; one of the first to propose a model of the Universe, namely, that the Earth was a disk afloat on a great sea.

Anaximander

the earth floats freely in space

Pythagoras

emphasized mathematics; used numbers and \n geometry to express relationships in nature.

Plato

emphasized metaphysics; the pupil of Socrates and \n Aristotle’s teacher; he emphasized the importance of the circle in models.

Eudoxus

developed a detailed mathematical theory for the motions \n of planets

Aristotle

emphasized metaphysics; he is credited with developing \n a well-thought-out model of the Universe (an Earth-centered geocentric model) that persisted until the 1500s

Aristarcus

put forward heliocentric model but wasn’t believed

* mainly because stars didn’t exhibit parallax, which was \n expected if the Earth went around the Sun because people incorrectly assumed \n the stars were relatively nearby

he applied geometry calculations to \n observations to deduce the relative sizes and distances of the Sun and Moon

Erathosthenes

emphasized mathematics; he made observations of \n the angle of the Sun with respect to zenith (overhead) at different latitudes which enabled him to __**accurately**__ __**calculate the circumference of the Earth**__

Hipparchus

emphasized mathematics; one of the first to catalog the \n brightnesses and positions of stars in a comprehensive way; __**credited with introducing the concept of epicycles**__

Alighieri (Dante)

he made drawings which showed the location \n of heaven and hell in the Aristotelian Universe based on theological teachings of Thomas Aquinas; this became one of the foundations of the church at that time

Digges

one of the first to seriously introduce __**the concept of infinity**__ into a model of the Universe

Bruno

he was the first to suggest that we live in a Universe with the Sun not at its center and that __**each star**__ (possibly an infinite number of them) __**represent different solar systems**__.

Lippershey

Dutch lens maker often credited as the first to build a refracting telescope (but not for astronomy)

Gallilei, Gallileo

he did important experiments which __**helped reveal** \n **the laws of falling bodies**__; he also made observations with a telescope (he put together the first refracting telescope used for astronomical observation) which supported the heliocentric theory

Newton

great synthesizer of experiments and observations who \n put forth the __**Theory of Gravity**__ (for example, he explained Kepler’s empirical 3rd Law and modified it so that it could be used to calculate the mass of a body); __**he also invented the reflecting telescope, calculus**__, and did important experiments in optics and light.

\[Earth-centered (geocentric) model which used rotating crystalline \n spheres\]

Aristotelian

\[Earth-centered (geocentric) model which used epicycles to explain \n the planets’ retrograde motions\] \n

Ptolemaic

\[Earth-centered (geocentric) model by Dante based on the theology \n of Thomas Aquinas, including a place for heaven and hell\]

Theocratic

\[Sun-centered (heliocentric) which used a rotating Earth and more \n naturally explained the planets’ retrograde motions\]

Copernican

concept of an infinite Universe

Digges

Concept of many solar systems

Bruno

\[circular orbits replaced by elliptical orbits\]

Keplerian

\[gravity theory explains motions on Earth and in the sky\]

Newtonian

Galileo’s observations

 law of inertia and motions of objects \n  many stars too faint to see without telescope \n  nebulous blurs resolved into many stars \n  Jupiter’s 4 largest satellites/moons \n  phases of Venus \n  surface of Moon is rough/irregular \n  sunspots

Newton’s 1st Law

inertia (objects resist changes in their motion)

Newton’s 2nd Law

F=ma (the acceleration that a force produces depends on \n the object’s mass)

Newton’s 3rd Law

for every action there is an equal and opposite reaction

Newton’s Law of Universal Gravitation

(gravitational force is proportional to \n mass and inversely proportional to distance squared)