Cosmic Perspective Chapter 3

ancient definition of a planet

wandering star

solar calender

A calendar synched with the seasons

lunar calender

A calendar synched with the lunar cycle

Metonic cycle

used to keep lunar calendars approximately synchronized with solar calendars. 19 yer period

scientific model

is a conceptual representation created to explain and predict observed phenomena

Geocentric Model

Any of the ancient Greek models that were used to predict planetary positions under the assumption that Earth lay in the center of the universe.

Thales

Legendary prediction of a solar eclipse, the universe fundamentally consists of water and Earth is a flat dick floating in an infinite ocean.

Anaximander

Thales student. Earth floats in empty space surrounded by a sphere of stars and two separate rings along which the sun and moon travel. (celestial sphere) Imagined Earth to be cylindrical

Pythagoras

adopted a spherical earth because a sphere is geometrically perfect

Plato

He asserted that all heavenly objects move in perfect circles at constant speeds. "heavenly perfection"

Eudoxus

Created the solution for retrograde motion. Created a model in which the sun, moon, and planets each had their own spheres nested within other spheres.

Aristotle

In his model, all the spheres responsible for celestial motion were transparent and interconnected like the gears of a giant machine. Argued hat gravity pulled together heavy things towards the center of the universe

Ptolemaic model

The geocentric model of the universe developed by Ptolemy in about 150 A.D.

epicycle

circle within a circle

Deferent

the circle around the earth in which a celestial body or the center of the epicycle of its orbit was thought to move

Hipparchus

developed Apollonius's circle idea that could predict planetary position

Copernican Revolution

The dramatic change, initiated by Copernicus, that occurred when we learned that Earth is a planet orbiting the sun rather than the center of the universe

Copernicus

Devised a model of the universe with the Sun at the center, and not earth.

Tycho

Decided to observe an alignment of Jupiter and Saturn. Realized that copernicus was wrong. Observed a nova (new star)

Kepler

Hired by Tycho. Labored with intensity to find an orbit for Mars. Tycho was wrong by 8 arcminutes which led Kepler to discover that planets orbit in ellipses

ellipse

A type of oval that happens to be the shape of bound orbits.

Foci

fixed points at the centers of an ellipse

semimajor axis

Half the distance across the long axis of an ellipse; in this text, it is usually referred to as the average distance of an orbiting object, abbreviated a in the formula for Kepler's third law. The average of the perihelion and aphelion

eccentricity

A measure of how much an ellipse deviates from a perfect circle; defined as the center-to-focus distance divided by the length of the semimajor axis.

Kepler's First Law

The orbit of each planet about the sun is an ellipse with the sun at one focus

Perihelion

orbital point nearest the sun

Aphelion

point in a planet's orbit that is farthest from the sun

Kepler's second law

A planet moves faster in the part of its orbit nearer the sun and slower when farther from the sun, sweeping out equal areas in equal times

Kepler's Third Law

More distant planets orbit the sun at slower average speeds, obeying the precise mathematical relationship: p^2=a^3 (p is orbital period in years) (a is AU)

Galileo's Evidence

experiments with rolling balls (Things would get left behind), built a telescope (shattered heavenly perfection), found that the stars were more numerous and distant than Tycho had believes (naked eye stellar parallax). Observed 4 moons orbiting Jupiter, and that venus goes through phases

Hypothesis

A testable prediction, often implied by a theory

Hallmarks of Science

1. Modern science seeks explanations for observed phenomena that rely solely on natural causes.

2. Science progresses through the creation and testing of models of nature that explain the observations as simply as possible.

3. A scientific model must make testable predictions about natural phenomena that would force us to revise or abandon the model if the predictions do not agree with observations.

Occam's Razor

Simpler explanations are more likely to be true than complex ones.

Pseudoscience

A fake or false science that makes claims based on little or no scientific evidence.

paradigm

a model; an example

Theory

A hypothesis that has been tested with a significant amount of data