Astrophysics and Historical Astronomy

These flashcards cover key concepts related to star brightness, historical astronomy, and the laws governing planetary motion.

Apparent Magnitude

A measure of how bright a star appears from Earth, with lower numbers indicating brighter stars.

Absolute Magnitude

A measure of the inherent brightness of a star, defined as how bright it would appear if it were 10 parsecs away.

Parsec

A standard unit of distance used in astronomy, equal to about 3.26 light-years.

Prograde Motion

The general west to east drift of planets over multiple nights, observed against the background of stars.

Retrograde Motion

The apparent backwards motion of planets relative to the background stars, observed over a few nights or weeks.

Geocentric Model

An astronomical model that places Earth at the center of the universe, with planets and the Sun orbiting around it.

Heliocentric Model

An astronomical model that places the Sun at the center of the solar system, with planets orbiting around it.

Kepler's First Law

Planets orbit the Sun in ellipses, with the Sun at one focus of the ellipse.

Kepler's Second Law

The line joining a planet to the Sun sweeps out equal areas in equal times, resulting in varying speeds of planets depending on their distance from the Sun.

Kepler's Third Law

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