ASTR 101 Final
Module 1
scale of the solar system
cosmic year
night sky
Earth’s path through the sky: ecliptic
as the Earth moves through the sky while orbiting the Sun, the stars we see and their positions changes
different patterns of constellations
circumpolar stars: stars near the north celestial pole that always stay above the horizon
eg: Polaris
zodiac: the constellations that appear at different times of year
reason for seasons
Earth is on a 23.5 degree tilt towards Polaris
Sun is higher in the sky in Summer which means more direct sunlight so its warmer
lunar phases: during the Moon’s orbit around the Earth, the angle between the Sun, Moon, and Earth changes so that different portions of the Moon are lit
moonrise/moonset times
the Moon moves slightly eastward in the sky each day so the time it rises/sets varies
the Moon’s phase dictates how far it is from the Sun, and thus when it rises (a New moon is closest to the Sun, and so rises/sets when it does)
synchronous rotation: takes exactly the same amount of time to rotate once as it does to orbit Earth once so we only see one side of it
eclipses: don’t happen every month because the angle of the Moon is tilted slightly compared to Earth, so the three aren’t perfectly aligned
Module 2
geocentric universe
everything in perfect spheres and circular orbits
to explain retrograde motions of planets, epicycles: smaller circular orbit on top of main orbit (deferent)
Copernican Revolution
Brahe took detailed observations on the positions of planets for years, Kepler used this data to come up with the laws of planetary motion
Copernicus’s heliocentric model still didn’t work bc of the circular orbit
Galileo used the telescope and found that the heavens were not perfect, Venus goes through phases too, and Jupiter also had moons, which provided scientific proof to heliocentric theory
Kepler’s Laws
1st- orbits are ellipses with the Sun at one focus
2nd- planets move faster when they are closer to the Sun
3rd- period and average distance from Sun are related: P^2 = a^3
Newton’s Version- P^2 = a^3/M
Definitions:
speed: rate at which an object moves
velocity: speed and direction
acceleration: change in velocity
momentum: product of mass times velocity
Newton’s Law and gravity
an object in motion stays in motion unless acted on by a net force
force = mass x acceleration
for every action there is an equal opposite reaction
energy and conservation laws
conservation of energy: kinetic, thermal, gravitational potential
conservation of momentum and angular momentum
conservation of energy
light
wavelength: distance between successive peaks
shorter: more energy, high frequency, blue/violet-er
longer: less energy, low frequency, red-er
matter
atoms, nuclei, electrons, molecules
changes
how high the temp is determines what bonds can be broken
rigid (melting), flexible (evaporation), removing electrons (ionization)
sublimation: very low pressures that do not allow for liquids means that things go straight from solid to gas
thermal (continuous) spectra: for hot, dense objects there will be no gaps in there spectrum
absorption line spectrum: look at a hot dense object through a diffuse cloud of gas, there will be gaps in the spectrum where the cloud has absorbed light at certain wavelengths
emission line spectrum: look at a diffuse cloud of gas, light will only be seen in a few colors on the spectrum that depend on what the cloud is made of
electrons can jump up or down between levels by aborbing or emitting energy
jumping down → energy has to go somewhere so becomes light (emission)
jumping down → wavelengths are absorbed
thermal radiation:
hot objects glow white and bright
cool objects glow red and faint
Doppler effect: as an object moves towards you, the spectrum is shifted to higher frequencies
redshift- moving away
blueshift- moving towards
lets us measure speed
faster an object spins, broader the absorption lines get
Module 3
refracting telescopes: light rays are bent as they pass from one substance to another (lenses)
downsides: different wavelengths of light are bent differently so images smeared out by color
reflecting telescopes: light rays bounce off of highly polished glass (mirrors)
space telescopes are better because they do not suffer from atmospheric turbulence, give sharper images, and see wavelengths of light that don’t get through the atmosphere
solar system overview:
orbits: all the major planets orbit in the same direction around the Sun, largely in the same orbital plane, and in the same direction
properties: terrestrial planets are small, dense, rocky; Jovian planets are large, low density, mostly gaseous
asteroids (rocky) found in inner solar system, comets (icy) found in outer solar system
oddballs:
planets spin in the same direction that they orbit (except Venus and Uranus)
planets are either terrestrial or Jovian (except dwarf planets)
planetary moons are much small than their planets (except the Earth/Moon)
formation of the solar system:
giant cloud of gas and dust around the proto-Sun is contracting and flattening, which releases energy which heats the disk
same composition as the Sun: 70% hydrogen, 28% helium, 2% everything else
inside the frost line, only things that could become solids were metals and rock; outside, it was cold enough for ices
there wasn’t much rocky stuff so those planets are smaller
lots of icy material so those giant cores pull in a lot of gas
late collisions formed the Moon and some weird tilts of planets
Module 4
planetary interiors
mantle: mid density, warm rock where the lithosphere “floats”
liquid metal outer core: convection happens here and in the mantle
solid metal inner core: high density, generates magnetic field
magnetic fields can happen if:
core is metallic
core is at least partially liquid
planet spins reasonably quickly (circulates the core)
shaping planetary surfaces
volcanoes: molten rock helps build surface
outgassing- when volcanos erupt they spew gasses into the atmosphere
impacts: produce craters on surface, most happened in early solar system
tectonics: motion from lithospheric parts creates surface features
erosion: processes due to weather
cooling down:
small planets have a larger surface area to volume ratio meaning they are loosing more heat to radiation than they can produce through their cores
comparative planetology
Venus: active volcanoes, some craters, little erosion, strange tectonics
Earth: active volcanoes, plate tectonics, ongoing surface changes
Mars: had this stuff but cooled down
terrestrial atmospheres
atmosphere creation: mostly outgassing from volcanoes
atmosphere loss: strong gravity helps keep the atmosphere in place
magnetic field helps stop the solar wind from stripping it away
greenhouse effect: certain gasses warm the atmosphere by stopping heat from escaping the surface and absorbing infrared light while letting visible light through
structure of Earth’s atmosphere, bottom to top:
troposphere: where weather is, heated by Earth’s surface
stratosphere: ozone layer due to plant/algae life producing oxygen
thermosphere: X-rays get absorbed, heating and ionizing the gas
exosphere: almost fading into space, where atmospheric gasses can escape into space
oxygen
the aurora: solar wind particles stream into the atmosphere at the poles, ionizing atoms and molecules
colors of the sky:
day: molecules in the atmosphere scatter blue light more than red so we see the blue light in the sky
sunset: when the sun is low on the horizon the light is passing through so much atmosphere that the blue light is scattered away and all we see is red light
weather due to rotation patterns
the faster the planet spins, the stronger the wind patterns
Earth’s Carbon Cycle:
CO2 in the atmosphere is turned into rain
rainfall erodes minerals and transports dissolved carbon into the ocean
minerals and carbon combine to make carbon-rich rocks on the ocean floor
plate tectonics move these rocks in the mantle (slowest part)
carbon-rich rocks melt in the mantle and are outgassed back into the atmosphere as CO2
Mars climate change
was once a warm, active planet with surface water
because it’s a small planet, interior cooled fast
volcanoes shut down → no more atmospheric creation
magnetic field dies out due to no more activity in the core → solar wind strips atmosphere away
Mars becomes cold, water freezes
Venus climate change
once had water, but too close to the Sun to be liquid so evaporated and was in the atmosphere as water vapor
water vapor trapped heat from the surface, amplifying the effect
volcanic outgassing released a lot of CO2 which also trapped heat and had no rain to wash it back to the surface so just kept building
Module 5
comparative planetology
cores: Earth-size rocky/icy cores covered by gasses
compositions:
Jupiter and Saturn: mostly hydrogen and helium with some metals
Uranus and Neptune: hydrogen, helium, methane w/ rocks and ices
temperatures/pressures:
Jupiter is so massive there are very high pressures that produce pressure changes going inwards:
gaseous hydrogen becomes liquid, liquid hydrogen becomes metallic or charged, then the core
Saturn has less mass so the interior has less pressure
more gas and liquid hydrogen but less metallic
Uranus and Neptune are much lower in mass so no metallic hydrogen, mostly gaseous and hydrogen compounds
Jupiter rotates very rapidly, creating strong winds and a strong magnetic field with its metallic hydrogen
moons: large moons formed along with their planet, small moons may have been objects that were captured by gravity
resonant orbits: Io, Ganymede, and Europa are constantly lining up, pulling them into an elliptical orbit
tidal heating: Io’s elliptical orbit means it can be tidally heated or being pulled and squashed constantly by Jupiter’s gravity
this heats up the 3 Galilean moons and keeps their interiors molten and geologically active
Saturn
rings: formed from collisions of icy moons, slowly ground down and disappear over time, more can be formed though
collisions keep the rings thin by keeping them moving horizontally,
gravitational interactions with moons create gaps from the moon’s gravity keeping them away or from Shepherd moons
Titan: only moon with atmosphere, mostly methane
at the triple point for methane
asteroids: rocky leftovers from planet formation
mostly found in asteroid belt, Jupiter’s gravity keeps tugging on them and stopping them from clumping to form a planet
comets: small icy objects from outer solar system
Kuiper belt: outside of Neptune’s orbit, orbit mostly in the plane of the solar system
Oort cloud: very outer solar system, more random orbits, originally formed where the Jovian planets are but their gravity ejected them
comet lifecycle: when comets get close to the Sun, the heat leads to long tails forming
solar wind sweeps back the plasma tail so usually points away from the Sun
as comets gradually boil away, the leave a trail of dust and rock behind them- as the Earth passes through this trail, we get a meteor shower
Pluto and the Kuiper Belt
impacts of asteroids/comets: most are small, leading to shooting stars, but sometimes big ones can happen such as the one that killed the dinosaurs
Module 6
the Sun
sunspots: dark areas where the Sun’s magnetic lines pop out, stopping hot gas from rising up
solar prominences: bright loops of plasma trapped along a magnetic line
solar flares: sudden, explosive release of energy
coronal mass ejections: surge in solar wind due to solar activity
Solar Cycle: 11 year cycle of solar activity
the sun rotates differentially, which distorts the magnetic field lines, kinking them up and making them pop out of the sun’s surface
powering the Sun: nuclear fusion of hydrogen into helium
high temps and pressure allow protons to come together
PP chain: fusion of two protons will eventually form helium and a high-energy gamma ray, which eventually gets to the convective zone where hot gas rises to the surface and releases the energy as sunlight
Solar thermostat:
fusion rates depend on temperatures: if temps drop, fusion rates go down
pressure depends on temperature: temps drop, pressure drops
contraction depends on pressure: pressure drops, Sun contracts bc the force of gravity is stronger than the inside pressure
temperature depends on contraction/expansion: contraction releases energy, heating the core
core heats up and fusion rates rise back to normal
Sun’s life
when the Sun starts running out of hydrogen, it will become a red giant while it burns through its helium
then, it’s outer layers will be pushed out making a planetary nebula leaving the small, dense carbon/oxygen core behind as a white dwarf
exoplanets
Doppler wobble: planet’s gravity pulls on the star making it wobble, which we can detect via the Doppler shift if the planet is “edge on”
planetary transits: star’s light will dim a bit as the planet passes in front, in both visible and infrared light
can learn:
orbit period and distance with the period of wobble/dimming plus Kepler’s 3rd Law
mass from wobble, size from dimming, which gives us density
temperature from infrared
atmosphere from spectroscopy
easiest to find big planets close to their star
habitable zone: region around a star where liquid water could exist
stars smaller than the sun are cooler so their habitable zone is closer to the star
findings:
planets can be much closer to their star, have very elongated orbits
tightly packed systems
Hot Jupiters: massive gas giants close to their star, could not have formed there so much have migrated inwards through interactions with the disk of formation
elongated orbits through gravitational encounters of planets