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Astronomy Week 18,19 lecture chapter 12.docx

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Department
Astronomy
Course
Astronomy 1021
Professor
Stacey Hallman
Semester
Fall

Description
Astronomy Week 18 – chapter 12 Solar System and Telescopes • All three techniques (imaging, spectroscopy, timing) are used in the study of the solar system Measuring Distances • We know the radius of Earth, and observations during the front transit allow us to measure this parallax angle • So using geometry, we can calculate the distance to Venus Measuring Sizes • With the aid of telescopes, we can measure the angular diameter of planets • Since we also know the distance, we can calculate the diameter in km Measuring Mass • Observe moons going around the planet  measure angular distances and orbits and periods  tells you the mass of the planet • From mass and size: we get density Rotation • Telescopes and spacecraft’s each have advantages and disadvantages o Telescopes:  Hampered by location (earth or earth orbit)  Cheaper, can be used long-term and upgraded  Lots of new objects still to find  Can study many objects o Spacecraft:  Can get close to solar system objects: • Better spatial resolution • In situ measurements  Bring back samples  Take a long time to build, launch, travel  Very expensive • Aflyby spacecraft mission comes close to a planet just once o Cheaper than other missions but less time to gather data • The Voyager 1 spacecraft is still operating and is currently 127AU from the Sun • Orbiter spacecraft go into orbit around another world o More time to gather data but cannot obtain detailed information about world’s surface Messenger’s Journey to Mercury • Probes or landers actually land on the surface of another world o Sequence: brake, fall, bounce, open, explore • Sample return missions land on the surface of another world and bring back samples • Combination spacecraft include more than one type, e.g. lander/orbiter o Cassini/Huygens mission to Saturn/Titan The Solar System • Consists of the sun and those celestial objects that orbit the sun • These objects: o 8 planets o 170+ known moons o 5+ dwarf planets o billions of smaller bodies: asteroids, comets, Kuiper Belt Objects • Scale: the sun is the size of a grapefruit (14 cm), earth is the size of a ball point, 15 m away • The sun is mostly hydrogen and helium and contains 99.9% of the solar system’s mass o Coverts 4 million tons of mass into energy each second • Mercury is made of metal and rock, with a large iron core: a bit bigger than the moon o Desolate, cratered; long, tall, steep cliffs o Very hot and very cold • Venus is nearly identical in size to earth but has its surface hidden by clouds o Hellish conditions due to greenhouse effect o Hotter than mercury • Earth has the only surface liquid water in the solar system and a surprisingly large moon • Mars is a cold desert o Giant volcanoes, canyons, polar caps o Water flowed in the past o There have been many mars missions • Jupiter is more massive than all the other planets combined: 300x Earth’s mass o Mostly hydrogen and helium; no solid surface o Many moons and rings • Jupiter’s moons can be as interesting as planets themselves, especially the four Galilean moons o Io: active volcanoes all over o Europa: possible subsurface ocean o Ganymede: largest moon in solar system o Callisto: a large, cratered “ice ball” • Saturn is giant and gases like Jupiter, and has rings and many moons o Its rings are made of small chucks of ice and rock and orbit like tiny moons • Uranus is an ice giant o Smaller than Jupiter and Saturn but larger than earth  Made of hydrogen and helium and hydrogen compounds  Extreme axis tilt  Moons and rings • Neptune is similar to Uranus, except colder and with less axis tilt o Many moons o Moon Triton: bigger than Pluto, orbits backwards • Pluto (and other dwarf planets) are icy and much smaller than the major planets o Pluto’s main moon (Charon) is almost as big as Pluto • The solar system contains small junk like asteroids and comets o Asteroids:  Small, rocky  Mostly in “main belt” between mars/Jupiter o Comets:  Small, icy  Father out, in Kuiper belt or Oort cloud • The four inner planets are rocky and comparable in size o Jupiter is much bigger and gaseous • Terrestrial Vs Jovian planets o Terrestrial:  Smaller size and mass  Higher density  Made of mostly rock and metal  Solid surface  Few moons and no rings  Closer to sun and together with warmer surfaces o Jovian:  Larger size and mass  Lower density  Made of mostly hydrogen, helium and hydrogen compounds  No solid surface (“gas giants”)  Rings and many moons  Farther from the sun and apart, with cool temperatures and cloud tops • Asteroids o Example: Eros, Ida and Dactyl o Irregularly shaped bodies mainly made of rock o Dust specks to dwarf planet sizes o Many in asteroid belt, but also in other places • Comets o “dirty snowballs”: made of ices mixed with rock o short-period comets:  orbit in same direction and plane as planets  originate from Kuiper Belt o long-period comets:  random orbits  originate from Oort cloud • Dwarf planets o There are currently 5 objects that are recognized as dwarf planets by the IAU: Ceres, Pluto, Haumea, Makemake, and Eris o These are objects that are massive enough o be rounded by their own gravity • Patterns of motion: o All planetary orbits are nearly circular and lie nearly in the same plane o All planets orbit the sun in the same direction: counterclockwise as viewed from high above the earth’s north pole o Most planets (and the sun) rotate in the same direction in which they orbit with fairly small axis tilts o Most of the solar system’s large moons exhibit similar properties in their orbits around their planets o EVERYTHING TURNS COUNTERCLOCKWISE • Four features of the solar system: 1. Patterns of motion among large bodies: sun, planets, and moons orbit and rotate in an organized way 2. Two major types of planets: terrestrial and Jovian 3. Asteroids and comets: location, orbits and compositions of these objects follow district patterns 4. Exceptions to the rules: e.g. sideways tilt of Uranus, retrograde of Venus, Earth having a large moon, etc. • Explaining the features: o Nebular hypothesis first proposed by Immanuel Kant in 1755 and later by Pierre-Simon Laplace o The nebular hypothesis basically says that the solar system is formed from the gravitational collapse of an interstellar cloud
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