Raw notes:

Exoplanets.org is a catalog of stars with planets. It behooves you to check the catalog to see if the star you setting your story around has planets so that you are at least consistent with what is existing. This won’t be all we know in the future, but it’s a good place to start.

International Astronomical Union is the name police of astronomy

More than 50% of all stars in our Milky Way are binary systems. center of mass=balance point of the system. Both masses equal => center of mass is in the middle, r_A =r_B

Kepler’s 3rd law. Period squared of a planet’s year in Earth year, is equal to its orbital radius. P_y²=a_AU³ He didn’t know why it worked, but it did. Valid for the solar system: star with 1 solar mass in the center. This works for a system with a single central objects.

Newton discovered that it also works around binary systems. M_A + M_B = a_au³/P_y² Using this, we can discover the sum of their masses. We can also discover where their center of gravity. This is how they found the mass luminosity relationship in the main sequence.

The ideal case: Both stars can be seen directly and their separation and relative motion can be directly observed.

Spectroscopic binaries. In that case, what you are looking for absorption lines. As the stars move toward and away from you these lines will be doppler shifted. That gives you the radial velocities.

Eclipsing binaries: A small hot star orbits a large cool star, and you see their total light. As the hot star crosses in front of the cool star, you see a decrease in brightness. When it passes behind, the light returns to normal.

Extra-solar Planets

Hard to see them next to a very bright star.

Two indirect techniques available. Like a binary star, but where the 2nd “star” has extremely low mass.

-Watch for Doppler wobble in position/spectrum of star.⁴⁴

-Watch for “transit” of planet which slightly dims light from star.

The first planet’s found tend to be bigger than Jupiter and very close to their suns. As the techniques get better, they get better at spotting smaller ones. The problem with spotting something out in a Jupiter-like orbit is that it takes 12 years for Jupiter to go around the sun, so you’d need to watch that star for at least 12 years.

When you look at the stars, you have to pick stars with their ecliptic edge on to us.

Stars are hotter than planets. Planets emit blackbody radiation. The Spitzer telescope is picking up blips of infrared which are consistent with planets.

Terrestrial Planet Finder. Likely use both interferometry and coronagraphs to image Earth-like planets.

Which planets can retain which planets.

You plot escape velocity against temperature Kelvin. That will tell you which gases a planet can retain. Jovian Planets can retain all gases.

Earth and Venus can retain all except H₂. Cold trap on Earth preserves our H.

Mars can retain C0_2. Barely retains H₂O

Titan and Triton only moons which can retain atmospheres.

Make sure that your planets make sense.4

1. Mike ran back and forth across the room and said that they can measure that degree of wobble across interstellar distances. That’s astonishingly precise.444

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