The Big Picture - Astro 3 Principles To Remember

(so far, this is a work-in-progress. Keep checking back. Hopefully it'll be in fairly final form by the time we begin class)

* Science is the art of asking Nature herself how she works. The steps: Observe, make hypothesis, find logical observable implications, and search for evidence these implications are in the real world.

* Occam's Razor - simpler explanations have a better chance of being true. Carl Sagan's corollary - extraordinary claims require extraordinary evidence.

* Gravity pulls stronger between objects when they're closer, or more massive.

* Gravity pulls on the near side stronger than the far side, so object is stretched - the "tidal force". The bigger the object, the more tidal stretching it will feel.

* Light has energy, but no mass. Travelling oscillating force fields which deliver energy when you "see". Shorter wavelength = higher energy.

* For an isolated system, the total angular momentum cannot change; it can shift around, but not change. Examples of approximately isolated systems: planets and their moons, binary stars, individual galaxies far from other galaxies.

* More massive objects cool slower. Example: more massive planets hold more of their original heat, and so have thinner crusts. Original heat is mostly due to impacts as the "solar nebula" material fell onto growing planets.

* Planetary atmospheres: At a given temperature, lighter elements (hydrogen and helium especially) move faster and escape the planet's gravity into space more easily: Only the cold outer planets were able to retain hydrogen and helium. Since H and He comprise the vast majority of the original material, means the outer planets are much more massive than the inner planets.

* Beyond Neptune, thousands of giant dirty snowballs a few hundred miles across or less - the Kuiper Belt. A hundred times farther away, the outer edge of the gravitational domain of the sun, and the realm of the Oort Cloud.

* We've found over 300 planets around other stars, mostly by seeing periodic wavelength shifts of spectral lines of the parent star. As planets move in front of their star, tiny eclipses can be seen, and are beginning to show what these planets are made of by spectra

* The sun - self gravity makes enormous weight and pressure and temperature on the innermost part, heating to over 10M Kelvins, enough to fuse hydrogen into helium converting some mass into energy = sunlight.

* Fermi Paradox - technology progress so vastly fast compared to age of stars and the galaxy, there ought to be many civilizations in the galaxy, nearly all vastly more advanced than we are. So why haven't they contacted us?

* Ingredients of life seem easy to form by normal chemistry, given warm wet planets. Still working out the details to evolve true living organisms