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p8 (universe expansion (different chemical elements absorb different…
p8
universe expansion
different chemical elements absorb different frequencies/wavelengths of light
each element produces a specific pattern of dark lines at the frequencies that it absorbs the visible part of the em spectrum
when we look at light from distant galaxies we see the same patterns but at slightly lower frequencies (longer wavelengths) than they should be
there's an observed increase in the wavelength of light coming from galaxies, light is shifted towards red end of spectrum, red-shift
measurements of the red-shift suggest all distant galaxies are moving away from us very quickly, same result looking in any direction
more distant galaxies have greater red-shifts than nearer one, bigger observed increase in wavelength
so more distant galaxies a moving away faster than nearer ones, evidence the universe is expanding
earth's temp
sun emits a spectrum of em radiation, some reflects off earth's atmosphere, some absorbed like uv and ir, some passes through to reach earth eg some uv, ir and visible light
overall temp depends on amount of radiation it reflects, absorbs and emits
during the day, more is absorbed, increase in local temp
at night, more is emitted, decrease in local temp
overall, fairly constant, one side absorbing, other emitting
some radiation absorbed is re-emitted, some this is absorbed by gases in the atmosphere like carbon dioxide, gases re-emit this radiation in all directions including back to earth, greenhouse effect, keeps earth warm
changes to the atmosphere can lead to changes in the earth's temp, eg increasing co2 levels in the atmosphere increase the amount of radiation the atmosphere absorbs, contributes to global warming
seismic
produces by earthquake, travel out through the earth, detected all over the surface of the planet using seismometers
when they reach a boundary between different layers of the earth, some are reflected, also change speed as properties of earth change, causes refraction
mostly change speed gradually, curved path, when properties change suddenly, path has a kink because of wave speed change
p waves : longitudinal, travel through solids and liquids, fast, refract slowly as the density of the mantle changes, refract sharply at boundary between mantle and core
s waves : transverse, travel through solids, slow
big bang
galaxies are moving away from each other at great speed, suggests something got them going from a single starting point
that something was probably a big explosion, the big bang
initially, all the matter in the universe occupied a single point, single point exploded, the big bang, space started expanding, expansion is ongoing
according to big band model, cmbr is the leftover energy of the initial explosion
emitting radiation
all objects emit em radiation
covers a range of energy values, wavelengths and frequencies
intensity and wavelength distribution depends on objects temperature
intensity is power per unit, y axis shows how much energy of emitted radiation transfers to a given area in a certain amount of time
as temp increases, intensity of every emitted wavelength increases, intensity increases more for shorter wavelengths because they transfer more energy
causes peak wavelength to decrease
microwave radiation
scientists can detect low frequency microwave radiation coming from all direction and all parts of the universe
known as the cosmic microwave background radiation (cmbr)
background radiation is strong evidence from an initial big bang, as the universe expands and cool, background radiation "cools" and drops in frequency
life cycle of stars
stars initially form from clouds of dust and gas
force due to gravity draws together the gas and dust, spiral together to form a protostar
temperature rises as star gets denser and particles collide with each other more often with more force, when temp is high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei, gives out massive amounts of energy, a star is born
cont
when a red giant runs out of fuel, becomes unstable, ejects outer layer of dust and gas as a planetary nebula, leaves behind a hot, dense solid core, white dwarf, cools down and eventually fades away
for red supergiants, when they run out fuel to fuse, collapse in on themselves in a massive explosion, supernova
exploding super nova throws the outer layers of dust and gas into space, leaves a very dense core called a neutron star, if star is big enough, this becomes a black hole, a super dense point in space not even light can escape from
absorbing radiation
all objects absorb radiation
object hotter than surroundings emits more radiation than it absorbs, cools down over time like tea
object cooler than surroundings absorb more radiation than it emits, warms up over time like ice cream
sonar
measure the depth of the seabed or detect things in the ocean
transmitter and receiver on a boat send out and detect pulses of sound waves
when they reach a boundary, reflected back to boat, by timing how long reflected waves take to return, distance can be calculated
cont
hydrogen in the core begins to run out, fusion of heavier elements occurs, star swells up and turns red (because surface cools), small to medium sized stars like the sun called red giants
bigger stars form red supergiants rather than red giants, start to glow brightly again during more fusion and expand and contract several times, form even heavier elements in nuclear reactions
cont
star enters period of equilibrium, energy released by nuclear fusion results in outward pressure that tries to expand the star, balanced by force due to gravity pulling everything inwards (gravitational collapse)
stable period called a main sequence star, lasts several billion years, sun in middle of this period
waves
at a boundary, can be reflected, partially or completely, continue travelling but at a different speed, sometimes causes refraction, or reflected
internal structure
shallow crust at surface, mantle beneath (solid properties but flow slowly), liquid metal outer core and solid metal inner core