Chapter 3: Orbits and Gravity Vocabulary Flashcards

A set of vocabulary flashcards covering key historical figures, laws of planetary motion, and gravitational principles from Chapter 3.

Tycho Brahe

A Danish nobleman who surveyed the sky without a telescope and gathered highly accurate observational data after observing a supernova in 1572.

Tycho's Star

A supernova observed in 1572 by Tycho Brahe, which led to funding for his observatory and accurate astronomical instruments.

Johannes Kepler

An assistant hired by Tycho Brahe who performed the mathematical analysis on planetary orbits after Brahe's death, developing the three laws of planetary motion.

Conic Section

Curves created by the intersection of a plane with a cone, including shapes such as a circle, ellipse, parabola, and hyperbola.

Ellipse

A closed conic section curve defined by two foci rather than a single central point, forming the orbital shape of planets.

Semi-major axis

The long radius of an ellipse, denoted as $a$, which describes half of its longest axis.

Semi-minor axis

The short radius of an ellipse, denoted as $b$, which describes half of its shortest axis.

Kepler's First Law

The law stating that each planet moves around the Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse.

Kepler's Second Law

The law stating that the straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time.

Kepler's Third Law

The law stating that the square of a planet's orbital period ($P^2$) is directly proportional to the cube of the semi-major axis of its orbit ($a^3$), written mathematically as $P^2 = a^3$.

Isaac Newton

The scientist who created new physical interpretations for the mathematical descriptions of astronomy made by Copernicus, Kepler, and Galileo.

Universal Law of Gravitation

A gravitational equation showing that there is an attractive force between any two masses in the universe, defined by $F = G \frac{M m}{r^2}$.

Apollo 15

The lunar mission during which an astronaut demonstrated that gravitational acceleration is independent of an object's mass by dropping a hammer and a feather on the Moon.

Closed Orbit Speed (Earth)

The required speed for an object to achieve a balanced closed orbit around Earth, which is $17,500\text{ miles per hour}$ ($8\text{ km/s}$).

Principia

The treatise published by Isaac Newton in 1688 containing his Universal Law of Gravity and Laws of Motion.

Edmund Halley

The astronomer who tracked part of a comet's orbit and successfully predicted its return using Newton's laws of motion.

William Herschel

The astronomer who discovered the planet Uranus in 1781.

Neptune

The planet discovered in 1845 less than $1^\text{o}$ away from its predicted position based on mathematical calculations of gravitational perturbations on Uranus.