Astronomy, Planetary Motion, and Radiation

Vocabulary practice flashcards covering famous astronomers, planetary motion laws, light scattering, and magnetic fields.

Geocentric model

A astronomical model stating that the moon, sun, and known planets (Mercury, Venus, Mars, Jupiter) orbit a stationary Earth, which failed to explain the retrograde motion of planets like Mars.

Retrograde motion

The apparent backward movement of planets relative to Earth, occurring because planets further from the Sun move slower in their orbits due to less gravitational pull.

Heliocentric model

An astronomical model stating that the Earth and other planets orbit the Sun.

Aristotle

Greek astronomer ($384\text{ -- }322\text{ BC}$) who was the first to conclude that the Earth was round by observing a lunar eclipse, though he still maintained belief in the geocentric model.

Aristarchus

Greek astronomer ($310\text{ -- }230\text{ BC}$) who was the first to hypothesize the heliocentric model, though others rejected it due to inaccurate measurements.

Eratosthenes

Greek astronomer ($276\text{ -- }194\text{ BC}$) who made the first successful attempt to determine the circumference of the Earth by measuring obelisk shadow angles at higher latitudes versus well illumination near the equator.

Copernicus

Greek astronomer ($1473\text{ -- }1543\text{ AD}$) who confirmed the heliocentric model using naked-eye observations, while maintaining a belief in circular planetary orbits.

Tycho Brahe

Danish astronomer ($1546\text{ -- }1601$) who measured the movement of Mars nightly without a telescope using custom instruments, accurately determining its elliptical orbit within a matter of degrees.

Johannes Kepler

German astronomer ($1571\text{ -- }1630$) and assistant to Tycho Brahe who discovered the 3 Laws of Planetary Motion and determined that planets closer to the Sun orbit faster.

Kepler's 1st Law

Law stating that all planets have elliptical orbits, meaning a planet's distance from the Sun changes throughout its orbit.

Perihelion

The point in a planet's elliptical orbit where it is closest to the Sun.

Aphelion

The point in a planet's elliptical orbit where it is farthest from the Sun.

Kepler's 2nd Law

Law stating that an imaginary line between the Sun and a planet sweeps out equal amounts of area in equal amounts of time, causing the planet to speed up near the Sun and slow down farther away.

Kepler's 3rd Law

Law stating that a planet's orbital period squared is proportional to its average distance from the sun cubed, represented by the equation $T^2 = D^3$.

Orbital period

The amount of time it takes for a planet to complete one full revolution around the Sun (e.g., $365.25\text{ days}$ for Earth).

Astronomical Unit (AU)

A unit of distance equal to the average distance from Earth to the Sun ($1\text{ AU}$).

Galileo Galilei

Italian astronomer ($1564\text{ -- }1642$) who advanced the telescope for astronomical studies, described moving objects, and provided observational support for Copernicus.

Isaac Newton

English scientist ($1643\text{ -- }1727$) who formulated the Law of Gravitation and the Laws of Motion.

Newton's 1st Law

Law stating that an object in motion tends to stay in motion and an object at rest tends to stay at rest unless acted upon by an outside force (inertia).

Newton's 2nd Law

Law stating that an object accelerates in the same direction as the applied force, where greater force results in greater acceleration.

Newton's 3rd Law

Law stating that for every action, there is an equal and opposite reaction.

William Herschel

German astronomer ($1738\text{ -- }1822$) who formulated the theory of stellar evolution and discovered that many nebulae were actually clusters of stars.

Edwin Hubble

American astronomer ($1889\text{ -- }1953$) who proved the existence of galaxies outside the Milky Way and established Hubble's Law, demonstrating that the universe is expanding.

Radiation

Energy released by atoms in the form of electromagnetic (EM) waves, categorized by wavelength.

Frequency

The number of wavelengths that pass a single measurement point in $1\text{ second}$.

Rayleigh scattering

Atmospheric scattering caused by incredibly small particles (gases, aerosols, pollutants) that refract white sunlight into different colors according to wavelength.

Mie Scattering

Atmospheric scattering caused by larger particles (such as water droplets in clouds and fog) that bounce white light while keeping all waves aligned, making clouds and fog appear white.

Earth's Magnetic Field

A protective shield generated by electric currents in Earth's rotating liquid outer core that shields the planet from harmful solar radiation and charged particles.

Auroras

Natural light displays formed near Earth's poles where the magnetic field is weaker, caused by interactions between solar wind and the magnetic field.

Magnetoreceptors

Biological compasses found in organisms like birds, sea turtles, and honeybees that allow them to detect Earth's magnetic field for seasonal navigation and migration.