Astronomy Overview and Fundamentals

Comprehensive practice flashcards covering astronomy basics, planetary motion laws, light properties, and spectroscopy based on the lecture notes.

Astronomy

The branch of science that studies everything in the universe that lies above Earth's atmosphere.

Universe Age

Approximately $13.7 \times 10^9\,\text{years}$.

Scientific Method

A set of rules used to guide science based on the idea that scientific ideas must be continuously tested, modified, or replaced if found inadequate.

Physics

The laws of the universe discovered using the scientific method that act as a rulebook for why things behave the way they do.

Hypothesis

An educated guess that must be testable and verifiable to be considered scientific.

Scientific Theory

A collection of well-tested hypotheses, laws of nature, and high-quality data that fit together to explain a wide range of natural phenomena.

Seasons

Caused by the orientation of the Earth's tilted spin axis with respect to the Sun as it orbits the Sun.

Waxing

A lunar phase characteristic where brightness is increasing over time.

Waning

A lunar phase characteristic where brightness is decreasing over time.

Gibbous

A lunar phase where the moon appears "fat," or approximately $\frac{3}{4}$ full.

Terminator

The line between shadow and light on the moon's surface that travels from right to left during the lunar month.

Lunar Month

A period of $29.5\,\text{days}$.

Line of Nodes

The 1-dimensional line where the Earth-Moon orbital plane intersects the Earth-Sun orbital plane.

Umbra

The dark, central part of an eclipse shadow where the Sun is completely obscured from an observer's view.

Penumbra

The dimmer, outer part of an eclipse shadow where an observer only sees a partial view of the Sun.

Antumbra

The dimmer, outer part of an eclipse shadow where observers see the entire Moon surrounded by an annulus (ring) of the Sun.

Annulus

A ring-shaped structure, specifically seen during an annular solar eclipse.

Geocentric Model

A solar system model, such as the Ptolemaic model, where the Sun, Moon, and planets orbit around the Earth.

Heliocentric Model

A solar system model, such as the Copernican model, where all planets orbit around the Sun.

Kepler's 1st Law

The orbit of a planet around the Sun is an ellipse with the Sun located at one focus.

Aphelion

The furthest point in an object's orbit from the Sun.

Perihelion

The closest point in an object's orbit to the Sun.

Kepler's 2nd Law

A line joining a planet and the Sun sweeps out equal areas in equal intervals of time.

Kepler's 3rd Law

The square of the orbital period ($P$) is directly proportional to the cube of the semimajor axis ($a$), expressed as $P^2 = a^3$ for planets in Earth years and AU.

Astronomical Unit (AU)

The average distance from the Earth to the Sun, approximately $150 \times 10^6\,\text{km}$ or $93 \times 10^6\,\text{miles}$.

Newton's 1st Law

An object continues in a state of rest or uniform motion in a straight line unless acted upon by a force.

Newton's 2nd Law

A force ($F$) acting on an object of mass ($m$) produces an acceleration ($a$) equal to the force divided by the mass ($F = m \times a$).

Newton's 3rd Law

For every action due to a force, there is an equal and opposite reaction force.

Newton's Law of Gravity

Every particle of matter attracts every other particle with a force directly proportional to the masses and inversely proportional to the square of the distance between them.

Escape Speed

The speed necessary for an object to escape the gravitational pull of another object.

Wavelength

The distance between two adjacent peaks or troughs of a wave.

Frequency

The rate at which the peaks of a wave pass by a point, measured in Hertz ($Hz$).

Photon

A packet of electromagnetic waves characterized by a specific wavelength, frequency, and energy.

Wien's Law

An equation used to predict the peak wavelength of thermal radiation as a function of temperature ($\lambda_{max} \approx \frac{0.29\,\text{cm}}{\text{Kelvin}}$).

Stefan's Law

States that the flux or brightness of an object emitting thermal radiation increases as the fourth power of its temperature ($F = \sigma T^4$).

Doppler Shift

The change in wavelength of sound or light due to the motion of an object relative to an observer.

Redshift

A Doppler shift where light waves are stretched to longer, redder wavelengths as an object moves away from the observer.

Blueshift

A Doppler shift where light waves are compressed to shorter, bluer wavelengths as an object moves toward the observer.

Nucleus

The small, compact center of an atom composed of protons (positive charge) and neutrons (no charge).

Ions

Atoms with a net positive charge that have lost one or more electrons.

Bohr Model

A quantum model of the atom where electrons occupy specific circular orbits corresponding to distinct energy levels.

Continuous Spectrum

A distribution of photons emitted at all energies in a region, typically produced by luminous solids, liquids, or dense gases.

Emission Line Spectrum

A pattern of colored lines produced by downward orbital jumps of an element's electrons, unique to each element.

Absorption Line Spectrum

A pattern of dark lines produced when upward orbital jumps in a cool gas absorb specific wavelengths from a continuous background light source.

Kirchhoff's 2nd Law

States that emission line spectra are produced by hot, low-density gases.

Kirchhoff's 3rd Law

States that absorption line spectra are produced by cool, low-density gases.