The Whole Darn Thing!
Chapter 3 – Cycles in the Sky
Earth rotates (one day), revolves (one year), and precesses (26,000 years).
The seasons are a consequence of Earth’s 23.5o tilt. Tides are caused by differential gravity.
The Moon revolves (one month), and also rotates so the same side is always facing us.
The Moon’s synodic period is one month; the sidereal period is only 27.5 days.
Eclipses would happen every month if the moon’s orbit were perfectly on the ecliptic.
Chapter 4 – The Origin of Modern Astronomy
The Ancients believed in the perfection of circles, and that stars were on a perfect sphere.
The retrograde motions of certain “stars” (the planets) were explained with epicycles.
Copernicus proposed a heliocentric system to replace Ptolemy’s geocentric system.
Brahe took accurate measurements of the stars, and Kepler derived his 3 laws from the data.
Galileo used a telescope to see moons of Jupiter and Venus is gibbous phase.
Newton’s gravity finally explained many theoretical issues in the geocentric model.
Chapters 5 & 6 – The Electromagnetic Spectrum
Light is just the visible section of a continuum of EM radiation.
Shorter wavelengths have higher energies. Gamma rays are most energetic; radio waves least.
All photons travel at the speed of light, so we are always looking into the past.
All telescopes – both reflecting and refracting - concentrate light into a small focus.
Hotter objects have higher-energy blackbody radiation.
Absorption and emission spectra are due to photon-atom interactions.
The Doppler Effect tells us how fast an object is moving towards or away from you.
Chapter 7 – The Sun
The Sun, like all “healthy” stars, is in hydrostatic equilibrium.
Hydrogen fusion produces helium in the Sun’s core;,the lost mass is released as energy.
Outside the core is the radiative zone, convective zone, photosphere, chromosphere, and corona.
The Sun’s strong magnetic field causes sunspots, solar flares, and the solar wind.
Chapters 8 & 9 – Stars
We can estimate star mass, atomic make-up, velocity, temperature, distance, size, and luminosity!
The Hertzsprung-Russell diagram plots luminosity (total energy output) against temperature.
The HR plot shows classes of stars: main sequence, giant, supergiant, and white dwarf.
The life of a star is determined mostly by its mass, but can be altered by binary companions.
Sun’s life: nebula  main sequence  giant  planetary nebula  white dwarf  black dwarf
Larger stars are hotter, use the CNO cycle instead of proton-proton chain, and “die” young.
Chapters 10 & 11 – Star Death
When a star’s core cannot burn more fuel, hydrostatic equilibrium fails, and gravity wins.
The fate of a dying star depends on the star’s remaining mass, and if it has a binary companion.
The smallest stars (<0.4 Msun) may never become giants, and end up as balls of helium.
Medium stars (<4 Msun) never fuse past carbon/oxygen, and end up as white dwarves.
Large stars (>4 Msun) fuse all the way to iron, then explode in type II supernova.
White dwarves are supported by electron degeneracy; neutron stars by neutron degeneracy.
Novae can only occur in binary systems, when a white dwarf “steals” mass from its companion.
Type Ia supernovae are like novae, but the entire white dwarf explodes, leaving no remnant.
Black holes are massive, but small. Nothing escapes the event horizon of a black hole.
Chapters 12 & 13 – Galaxies
The Milky Way galaxy is a typical spiral galaxy, with a central bulge, flat disc, and halo.
Galaxies have too much gravity considering how much mass we see; what is this “dark matter?”
Stars in the halo are mostly population II stars in globular clusters. The halo is old!
Stars in the disc are mostly population I stars, and young bright ones are in the spiral arms.
Elliptical galaxies are very common, contain little gas and dust, and have few young stars.
It is not surprising that Earth (a metal-rich planet) is on the arm of a spiral galaxy!
Most galaxies (all?) have a supermassive central black hole. Ours is 2,600,000 Msun.
There are a few hundred billion galaxies in the observable universe.
The Milky Way galaxy is in the Local Group, which is part of the Virgo Supercluster.
Farther galaxies tend to be red-shifted more, leading to “Hubble’s constant.”
Chapters 14 & 15 – The Cosmos
Some galaxies radiate tremendous energies from their nuclei, called “active galactic nuclei.”
The source of this energy is probably matter falling into a central, supermassive black hole.
Seyfert galaxies, BL Lac objects, blazars, and quasars are all fueled by active galactic nuclei.
Quasars are powerful AGNs with one jet pointed at us: they are the most distant objects we see.
Big Bang  pair production  3 crazy minutes!  recombination  dark age  reionization
The universe could be open (saddle), flat (sheet of paper), or closed (sphere). We think it’s flat.
Chapters 16, 17, 18, & 19 – The Solar System
The Solar nebula hypothesis says the Solar system “evolved” from the same rotating disc.
Planets basically form through condensation, accretion, and differentiation.
Terrestrial planets form inside the ice line. Dense, small, no rings/moons, little H and He.
Jovian planets form outside the ice line. Light, large, moons/rings, mostly H and He.
Mercury, Venus, Earth, Mars, ice line, asteroid belt, Jupiter, Saturn, Uranus, Neptune, Kuiper belt
Besides planets, we have moons, asteroids, comets, dwarf planets, lots of fun stuff!
Chapter 20 – Life
Life (as we know it) is based on DNA. DNA is made of amino acids.
Amino acids are common, can be created in labs on Earth, and have been found in meteorites.
Life evolves, being shaped by (and shaping!) its environment.
We study extremophiles on Earth to see what kind of life evolves in “extreme” environments.
Planets are abundant. We find mostly large planet because they’re easier to find.
We have not found evidence of life outside Earth… yet. 
Chapter 21 - …
It’s not written yet! But science keeps on keeping on. New discoveries are just around the bend,
and certainly we have much more to learn (we always will!). And, of course, much to unlearn…
All is but a woven web of guesses
- Xenophanes