Astronomy Finals Study Guide Flashcards

Astronomy flashcards based on the provided lecture notes to help you study for your upcoming test!

Universe

The totality of all space, time, matter, and energy.

Galaxy

A massive collection of stars bound by gravity; we live in the Milky Way.

Solar System

The Sun and all objects gravitationally bound to it (planets, moons, asteroids, etc.).

Earth's Location

Third planet from the Sun.

Astronomical Unit (AU)

Average distance from Earth to Sun (~150 million km).

Light-Year

Distance light travels in one year (~9.46 trillion km).

Big Bang Theory

Universe began ~14 billion years ago in a hot, dense state and has been expanding since.

Stellar Nucleosynthesis

Elements formed in stars and supernovae.

Daily Rotation

Earth spins on its axis once every 24 hours.

Orbital Motion

Earth orbits the Sun once per year at ~100,000 km/hr.

Galactic Orbit

Sun orbits the Milky Way every ~230 million years.

Constellations

Groupings of stars forming patterns; culturally defined.

Zodiac

12 constellations along the Sun’s annual path through the sky (ecliptic).

Daily Changes in the Sky

Caused by Earth’s rotation.

Annual Changes in the Sky

Caused by Earth’s orbit around the Sun.

Naked-eye observations

Over 2000 stars visible to the unaided eye.

Constellations (Sky division)

88 official constellations that divide the entire sky into regions; used for navigation and tracking celestial objects.

Altitude

Angle above the horizon.

Direction(Azimuth)

Compass point along the horizon.

Earth's Rotation and Star Movement

Rotates west to east leading stars to appear to move east to west.

Circumpolar stars

Near the North Celestial Pole; never set.

Latitude

Determines which part of the celestial sphere is visible; higher latitude means different visible stars and constellations.

Time of Year Implications on Constellations

As Earth orbits the Sun, the Sun's apparent position changes causing nighttime constellations to shift with the seasons.

North Celestial Pole

Aligns with Earth's North Pole.

South Celestial Pole

Aligns with Earth's South Pole.

Celestial Equator

Projection of Earth’s equator onto the sky.

Ecliptic

The Sun’s apparent annual path through the sky.

The Milky Way

Appears as a band of light encircling the sky and marks the plane of the Milky Way Galaxy.

Altitude in Local Sky

Angle above the horizon in the local sky.

Direction (Azimuth) in Local Sky

Compass point along the horizon in the local sky.

Meridian

Arc from north to south through zenith (overhead point).

Zenith

Point directly overhead.

Horizon

Boundary where sky meets Earth

Angle Basics

Full circle = 360°

Degrees to Arcminutes

1 degree (°) = 60 arcminutes (')

Arcminutes to Arcseconds

1 arcminute (') = 60 arcseconds (")

Estimating Angular Size

Sun and Moon: ~0.5°

Angular Size vs. Distance

Objects appear smaller at greater distances.

Causes of the Seasons

Earth’s axial tilt (23.5°) is the key factor.

Precession

Gradual wobble of Earth’s axis over ~26,000 years.

June Solstice

Sun farthest north, longest day in N. Hemisphere.

December Solstice

Sun farthest south, shortest day in N. Hemisphere.

March & September Equinoxes

Sun rises due east, sets due west, equal day/night worldwide.

Moon Phases

Caused by Moon’s orbit around Earth; half of Moon is always lit; visible phase depends on angle to Earth.

Lunar Eclipse

Occurs at full moon; Earth blocks sunlight → casts shadow on Moon.

Solar Eclipse

Occurs at new moon; Moon blocks sunlight → casts shadow on Earth.

Synchronous rotation (Moon)

Same side of the Moon always faces Earth.

Saros cycle

Eclipse pattern repetition; ~18 years.

Retrograde motion

Occasionally, planets move westward (looping); due to Earth “lapping” slower outer planets in orbit.

Scientific Thinking

Built on everyday reasoning— trial and error, logical patterns but differs by being methodical, systematic, and evidence-based

Astronomy's Practical Role

Among the earliest sciences, rooted in timekeeping, calendars, agriculture, and navigation.

Naturalistic Philosophy

Greeks sought explanations rooted in logic and observation, not mythology; emphasized mathematical models to describe the cosmos.

Greek Geocentric Model

Celestial bodies move in perfect spheres or circles around Earth; belief in celestial perfection and immutability.

Ptolemaic System

Introduced epicycles (small circles) and deferents (larger orbits) to explain retrograde motion; remained dominant for over 1500 years.

Nicolaus Copernicus (1543)

Proposed Sun-centered (heliocentric) model; retained circular orbits, so predictions were not significantly better than Ptolemy's.

Tycho Brahe

Made precise naked-eye measurements of planetary positions and proposed a hybrid model: planets orbit the Sun, which orbits Earth.

Johannes Kepler

Used Brahe's data to develop a more accurate model based on elliptical orbits.

Kepler’s First Law – Law of Ellipses

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

Kepler’s Second Law - Equal Areas Law

A planet sweeps out equal areas in equal time → moves faster near perihelion, slower near aphelion.

Kepler’s Third Law - Harmonic Law

More distant planets orbit at slower average speeds.

Galileo’s Experiments

Showed objects remain in motion unless a force acts (refuting Aristotle’s physics).

The Scientific Process

Seeks natural causes, builds models tested by observations and experiments and generates testable predictions.

Falsifiability

A hallmark of science—must be disprovable in principle.

Scientific Theory

A well-tested, evidence-based explanation of natural phenomena.

Speed

Distance / Time

Velocity

Speed with direction

Acceleration

Rate of change in velocity (e.g., m/s²)

Thermal energy

Total kinetic energy of particles

Temperature

Average kinetic energy.

Mass

Amount of matter in an object

Weight

Force exerted by gravity on an object

Newton's Law of Gravity

Every mass attracts every other mass.

Escape velocity

Enough energy to leave bound orbit

Wavelength

Distance between wave peaks

Frequency

Vibrations per second

Atoms

Nucleus (protons + neutrons) + electrons

Molecules

Two or more atoms bonded together

Phases of Matter

Solid, Liquid, Gas, Plasma

Continuous Spectrum

All wavelengths (e.g., lightbulb)

Emission Line Spectrum

Bright lines at specific wavelengths (hot gas)

Absorption Line Spectrum

Dark lines where light is absorbed (cool gas in front of hot light source)

Doppler effect

Measures speed of objects through light wavelength shift

Light-Collecting Area

larger area → gathers more light

Angular Resolution

ability to distinguish fine details

Refracting Telescope

Uses lenses; long, heavy, rare today

Reflecting Telescope

Uses mirrors; compact, common

Light Pollution

Caused by human-made lighting and satellite constellations

Multiple Telescopes – Interferometry

Combines multiple telescopes to simulate a larger one to improve angular resolution

Gravitational Waves

Found as ripples in spacetime and detected by LIGO.

Solar System structure

8 major planets with nearly circular orbits that all orbit in the same direction and in nearly the same plane.

Mercury

Metal/rock; extreme temperatures; many craters

Venus

Earth-sized; thick cloud cover; strong greenhouse effect

Earth

Life-supporting; oceans and atmosphere

Mars

Cold and dry; polar caps; evidence of ancient water

Jupiter

Largest; mostly gas; 4 major moons (Io, Europa,

Saturn

Rings made of ice/rock chunks; many moons including Titan

Uranus

Extreme axis tilt; H/He and hydrogen compounds

Neptune

Similar to Uranus; contains moon Triton

Dwarf planets

much smaller than major planets, icy and similar to comets

Clues to Solar System Formation

orbit the same direction and plane, have Terrestrial and Jovian planet types