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Notes on the sun + planets


Department
Astronomy & Astrophysics
Course Code
AST101H1
Professor
Stefan Mochnacki

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๎€Escape speed does not depend on direction
๎€Orbits are a kind of free fall/falling
๎€We have seasons because of earthโ€™s tilt towards the sun thus receiving more direct
sunlight: so july is warm because the northern hemisphere is tilted toward the sun
receiving more direct sunlight and longer days
๎€Distance of earth from sun does not really change, does not affect seasons
๎€Mars also has seasons, Neptune
๎€We see phases of the moon because of its elliptical orbit around earth
๎€We see one side of moon because of synchronous rotation, rotates once with each
orbit
๎€Two conditions for an eclipse: 1) must be full moon for lunar eclipse and new moon
for solar eclipse 2) the moon must be at the point in its orbit where it crosses the
ecliptic plane and its NODES , cant be below or above = no eclipse, eclipses occur
during the eclipse seasons โ€“ 2 each year
๎€Annual parallax of star: less than one arcsecond
๎€Hot gas = emission spectrum, hot dense object = continuous spectrum
๎€Venus: thick co2 atmosphere, mars: thin co2 atmosphere
๎€Plate tectonics help scrub carbon out of earth keeping it cooler than venus, making it
possible for us to live
๎€Carbon cycles keeps earthโ€™s temperature at a level we can live at
๎€Mars has no plate tectonics, life, or water, 95% of atmosphere co2
๎€Mars is not hot like venus because of its thin atmosphere not being able to trap heat
๎€Small mass, does not hold onto gases well, weak gravity
๎€Jovian planets: layers of liquid and gas, solid core
๎€Terrestrial planets: solid surface
๎€Unlike the other Galilean moons, callisto has no tidal heating or orbital resonances,
no internal heating
๎€Europa could have sub surface ocean, has a magnetic field
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