Download Unit Review #4

PHYSICS 127
DESCRIPTIVE ASTRONOMY
Review Sheet #4
Key Concepts and Formulae
Sky Familiarity:
Where and when to observe each of the naked-eye planets.
Lunar phase, location and times of moonrise and moonset.
Constellations, stars and extended objects as identified in the Course Outline
The Milky Way (MW) Galaxy:
Sky location, appearance and nature of the MW. The stellar and non-stellar components.
Size and structural features of the MW: the nucleus, bulge, disk, spiral arms, halo and corona. Shapley's discovery of the
direction and distance of the galactic center.
The expected face-on and edge-on general appearances of the MW. The sun's location.
Interstellar dust. Obscuration. Reddening of starlight. Location of the dust. Dark & reflection nebulae.
Interstellar gas. Molecules. Neutral hydrogen and its 21-cm radio emission line. Location of the gas. Emission nebulae.
Galactic rotation. Motion of the sun. Proper motions. Radial, tangential and space velocities. Non-Keplerian rotation and
dark matter. Candidates for the dark matter.
Spiral structure. Mapping spiral structure. Spiral arm tracers. The local spiral arms. Spiral pattern rotation versus galactic
rotation of stars. Possible causes of spiral structure. Density waves. Differential rotation of star-forming clouds.
Galaxy collisions. Grand design versus flocculent spirals.
The galactic nucleus. Direct observations. Number density of stars. Synchrotron radio emission.
Evidences for a supermassive nuclear black hole.
The galactic corona. Size and mass.
Evidences for dark matter in the galaxies: the galactic rotation curve, stability of the galactic disk, motions of nearby galaxies,
stability of clusters of galaxies.
Stellar populations. Population differences: spectral, chemical composition, motions, spatial distributions within Galaxy, ages,
types of stars and types of star clusters. Reasons for the population differences.
Galactic formation and evolution. Plausible galactic models.
Galaxies:
The “Great Debate” regarding "spiral nebulae”: Kant's "island universes." Hubble's resolution of M31 Cepheids.
Morphological types: The distinguishing characteristics of ellipticals (E), lenticulars (S0 and SB0), spirals (S), barred spirals
(SB) and irregulars (Irr). Ranges in size, star number and mass for each type. Hubble's "tuning fork" classification scheme.
Peculiar galaxies (Pec). Possible causes of the diversity of types.
S and SB subtypes a-c: variations in nuclear and arm prominence, tightness of arm wrapping, color, interstellar content and
clumpiness.
The spatial distribution of galaxies: clusters, superclusters and voids. Regular versus irregular clusters. The Local Group. The
Local (Virgo) supercluster.
Collisions between galaxies and their consequences: Merging (cannibalism). Induced spiral structure. Intergalactic stars.
Starbursts. X-ray emission from clusters.
Motions of galaxies. The Hubble law and its implications.
Distance indicators (standard candles) in galaxies: Cepheids, red and blue supergiants, novae, globular clusters, HII regions,
supernovae, bright galaxies in clusters. Tully-Fischer relation.
Definition of "active galaxy." Active galaxy types: Radio galaxies, quasars, Seyfert galaxies, blazars
Radio galaxies: their discovery, size, structure, nature of radiation. Head-tail sources. Jets.
Quasars: their discovery, spectra, variability, and redshifts. "Fuzz" and jets. Multiple redshifts. Quasar luminosities. Scarcity
or non-existence in the present-day universe.
Active galaxy models: the supermassive black hole--structure, evidences for, successes; frequent supernovae outbursts; stellar
collisions.
vr=Hr (the Hubble law). (Use H=73 km/s/Mpc.for any calculations.) SizecΔt.
Cosmology and the Early Universe:
Olber's paradox. The lookback time.
The expanding universe. The raisin-bread analogy. The age of the universe. “Center” of the universe.
The cosmic microwave (2.7K) background, and its discovery.
The mass distribution in space. Cluster, superclusters and voids.
The early universe: matter versus radiation domination, the radiation-matter transition, the "era of recombination" and the
microwave background, pair production and matter-antimatter annihilation, the standard big bang and inflationary models.
The fundamental forces: gravity, electromagnetism, the nuclear strong force, the nuclear weak force. Force "freeze outs."
v = H0d, T01/H0 (upper limit to age of universe) = 13.7 ×109 yrs (for H0 = 73 km/s·Mpc)