Chapter 16 — A Universe of Galaxies
Hubble's Classification — system of grouping galaxies by shape (spiral, elliptical, irregular).
Spirals — 20% of all galaxies; lots of dust and gas; "normal" is most abundant kind of spiral.
Elliptical Galaxies — 80% of all galaxies; most are dwarfs; super-large ones eat others.
Irregular — no shape; near collisions or collisions made them. Our satellite galaxies are the Magellanic Clouds and are irregular.
Standard Candles — each type of galaxy has a certain absolute magnitude (used for distances).
Clusters — galaxies are not alone but found in clusters.
Supercluster — clustering of clusters.
Hubble's Law — the farther the galaxy, the faster it recedes.
Hubble's Constant — 50 to 100 km/s/Mpc (modern best estimate ≈ 70).
Cepheids — variable stars with periods of 1–100 days; "yardsticks" to other galaxies.
Period-luminosity — how we use Cepheids to measure distance (period predicts luminosity).
Cosmological principle — universe is homogeneous and isotropic on large scales.
Cosmological redshift — all distant bodies are moving away — farther means faster.
Cosmological horizon — how far back we can see (limited by age of universe).
Lookback time — time since the light started its journey to us.
Radio galaxies — colliding galaxies (main reason for strong radio emission).
Quasar — "quasi-stellar objects"; small energetic cores of early galaxies (powered by supermassive black holes).
Chapter 17 — Birth of the Universe
Matter — that which dominates the baryonic materials in our universe.
Antimatter — opposite to our matter (annihilates on contact, producing photons).
Big Bang — universe expands out rapidly from a hot dense state.
Planck era — earliest era of the universe (before 10⁻⁴³ s); physics unknown.
GUT — Grand Unification of all forces (strong + weak + electromagnetic).
Inflation — time at the beginning when the universe expanded extremely quickly.
Cosmic Microwave Background (CMB) — leftover of early hot universe — about 3 K now.
Olbers' paradox — why is the night sky dark? Cannot have infinite size and infinite number of stars (universe has finite age and is expanding).
Chapter 18 — Dark Matter, Dark Energy, Fate of the Universe
Dark matter — makes up ~90 percent of universe's matter.
Dark energy — makes up ~60 percent (review sheet says "60% of dark matter" but modern figure is ~68% of total energy budget).
Rotation curve — stars do not slow down as they orbit the galaxy center → dark matter.
Orbits in clusters — galaxies orbit each other faster than visible mass predicts → dark matter.
Gravitational lensing — light is bent by galaxies more than it should be → dark matter.
MACHOs — Massive Compact Halo Objects; one candidate for dark matter.
Baryonic matter — normal matter; about 10 percent.
WIMPs — Weakly Interacting Massive Particles; another candidate for dark matter.
Large-scale structures — clusters of galaxies and clusters of clusters (superclusters), plus filaments and voids.
Critical density — matter density needed to open or close the universe.
Recollapsing universe — density above critical → expansion stops, universe re-collapses.
Critical universe — flat universe — what we think it is — barely expanding forever.
Coasting universe — expands forever at constant rate.
Accelerating universe — expansion goes faster over time (driven by dark energy).
Chapter 19 — Life in the Universe
Natural selection — Darwin proposed.
Mutation — biology changes life (raw material for evolution).
Habitable zone — area around a star where life can exist (liquid water).
Drake equation — probabilities of life that communicates in the universe.
Study workflow
Shortest review sheet — easiest test to over-prepare for. Drill Flashcards filtered to U5 → Practice Exam → take Test 5. After this, you've finished ASTR 1350 — congratulations!