Chapter 1 — Our Place in the Universe
Light-year — 6 trillion miles; how far light travels in a year's time. Used outside the solar system.
AU (Astronomical Unit) — 93 million miles; Earth–Sun distance. Used inside our solar system and near.
Rotation — object spins on its axis.
Orbit (revolution) — goes around another object.
Ecliptic — path of the Sun through the sky; the zodiac.
Tilt — causes seasons; 23.5° for Earth.
Chapter 2 — Discovering the Universe for Yourself
Celestial sphere — imaginary globe around Earth.
North & south celestial poles — points above the geographic poles; Polaris sits at the north celestial pole.
Celestial equator — Earth's equator projected outward and drawn on the celestial sphere.
Zenith — point directly overhead for an observer.
Meridian — line drawn from north to south through the zenith.
Local sky — the part of the celestial sphere an observer sees.
Altitude — how far above the horizon an object is.
Direction — starts from north and is measured around the horizon.
Circumpolar — part of sky that never sets; depends on latitude.
Reasons for seasons — KNOW what causes the seasons (axial tilt, NOT distance).
Summer + winter solstice — know dates for Northern Hemisphere (Jun 21 / Dec 21) and meaning.
Spring + fall equinox — know dates for NH (Mar 20 / Sept 22) and meaning.
Precession — 26,000 years for Earth's axis to wobble.
Phases of the Moon — know any direction on a diagram.
Lunar eclipse — know the diagram (Earth shadow on Moon, full Moon only).
Solar eclipse — know the diagram (Moon shadow on Earth, new Moon only).
Umbra / penumbra — umbra = full shadow, penumbra = partial shadow.
Retrograde motion — backward motion of planets as we pass them.
Parallax — best way to measure distance (apparent shift against background).
Chapter 3 — The Science of Astronomy
Stonehenge — ancient calendar in England.
Geocentric — Earth-centered system.
Ptolemaic model — used Earth at the center and epicycles.
Deferent — large circle.
Epicycle — small circle (circles on circles).
Eratosthenes — measured Earth's circumference and found it was a sphere.
Copernicus — put Sun at center — heliocentric.
Tycho Brahe — made the observations used by Kepler of planetary motion.
Kepler — used Brahe's data, proved heliocentric, and discovered three laws.
Kepler's three laws — know them:
- Ellipse — orbits are ellipses with Sun at one focus.
- Equal areas and times — sweeps equal areas in equal times.
- Law of ratios — p² = a³.
Galileo — used the telescope; was a physical scientist.
Galileo's discoveries — know what he found (phases of Venus, moons of Jupiter, sunspots, lunar craters, Milky Way stars).
Scientific Method — know its progression (observe → hypothesize → test → revise).
Paradigm — new idea / framework.
Hypothesis — a proposal.
Theory — data proves the hypothesis (well-supported by evidence).
Chapter 4 — Motion, Energy & Gravity
Velocity — distance / time (with direction).
Acceleration — velocity / time (change in velocity).
Momentum — mass × velocity.
Force — mass × acceleration.
Mass vs weight — mass = amount of matter; weight = gravity acting on mass.
Weightless / free-fall — you cancel the effects of gravity.
Newton's three laws:
- Body in motion stays in motion — inertia.
- F = m·a.
- Action–reaction (equal and opposite).
Angular momentum — amount of spin.
Kinetic energy — energy of motion.
Potential energy — energy of position.
Radiative energy — light.
Temperature — speed of molecules (avg KE).
E = mc² — know what symbols stand for (E = energy, m = mass, c = speed of light).
Law of gravity — know what symbols stand for and who proposed it (Newton, F = G·M₁·M₂/r²).
Escape velocity — velocity needed to escape a body (Earth ≈ 11 km/s).
Tidal forces — pull of gravity and its differential effect across Earth.
Neap tides — 20% lower than normal (quarter Moons, Sun ⟂ Moon).
Spring tides — 20% higher than normal (new + full Moon, Sun + Moon aligned).
Study workflow
Drill these terms in Flashcards (filter by U1 tags) → take Practice Exam in Adaptive mode until you score 100% → review the Cheat Sheet the night before → open Canvas and take Test 1.