Studied by 6 people
Distinguish between solar system and galaxy
galaxy is much larger in size than a solar system
galaxy contains many solar systems
galaxy is more luminous
Distinguish between a comet and a planet
a comet is a small icy body whereas a planet is mostly made up of rock or gas
a comet is often accompanied by a tail while a planet is not
a comet generally has a larger orbit than a planet
a planet must have cleared other objects out of the way of its orbital neighbourhood
Why values of distance might be different
small measurements used thus uncertainty in measurement
parallax angle very small
uncertainties in measuring
values same order of magnitude so not significantly different
Distinguish between constellation and stellar cluster
Constellation stars are not gravitationally bounded while stellar clusters are
Cluster stars are of similar age while those in constellations are not
Constellations form a visible pattern while stellar clusters do not
Stellar clusters are close in space while constellations aren not
Outline processes that produce the change in luminosity with time of Cepheid variable
Cepheid variables contract and expand
surface temperature decreases then increases
surface becomes transparent then opaque
Explain how Cepheid variables are used to determine distances
Peak luminosity depends on period
More luminous Cepheid variables have greater period
Measurements of apparent brightness allow distance determination
Explain why Cephids are used as standard candles
known as luminosity
determined from period-luminosity graph
used to estimate distance of galaxies
Suggest the conditions that will cause the Sun to become a red giant
Fusion of hydrogen in core eventually stops and core contracts
Sun expands and surface begins to cool
Helium fusion begins in the core
Sun becomes more luminous
Outline why Sun will maintain a constant radius after it becomes a white dwarf
electron degeneracy prevents further compression
State why there is a maximum distance that astronomers can measure using a stellar parallax
difficulty in measuring really small angles
Describe how chemical composition of a star can be determined
obtain line spectrum of a star
compare to laboratory spectra of elements
Describe satages of evolution from leaving main sequence until final stable stage
red giant
planetary nebula
white dwarf
Outline how equilibrium of main sequence stars is achieved
outward radiation pressure is balanced by inward gravitational force
Determine why stellar parallax is not suitable for all stars
stellar parallax limited to closer stars
State what is meant by main sequence stars
star fusing hydrogen into helium
State what is meant by a binary star
2 stars orbiting common centre of mass
State 2 characteristics of CMB radiation
black body radiation of approximate temp of 2.7K
uniform throughout (isotropic)
Describe how CMB provides evidence for Big Bang model
universe is expanding so wavelength of CMB in the past is much smaller indicating very high temperature at the beginning
due to expanding universe wavelength becomes longer when measured in the present time
State what is meant by the Big Bang model of the universe
theory in which all space created at a singularity at an enormous temperature
universe has been expanding ever since
State 2 features of CMB radiation consistent with Big Bang model
CMB has black body radiation spectrum
wavelength stretched by explosion
highly homogenous
State the nature if anisotropies observed in the CMB radiation
Temperature of CMB is not constant in different dierections
Identify 2 possible causes of ansiotropies
quantum fluctuations that have expanded
density perturbations that resulted in galaxies and clusters of galaxies
Outline how line spectra of distant galaxies are used to confirm hypotheses about the expansion of the universe
spectra of galaxies redshifted compared to spectra on Earth
redshift interpreted as cosmological expansion of space therefore universe expands
State what is meant by critical density
density of the flat universe
Discuss how scientists use galactic rotation curves to explain how less than 20% of matter can be observed
rotation speed of galaxies is larger than expected away from centre
thus there must be more mass at the edges of the universe than observable thus indicating the presence of dark matter
Light from distant galaxies is redshifted. Explain cosmological origin of this redshift
according to general relativity space expands stretching distances between far away objects
wavelength of photos received than emitted are therefore longer leading to observed redshift
Outline what is meant by dark energy
energy filling all space
resulting in repulsive force opposing gravity
accounts for accelerating universe
State 2 candidates of dark matter
black hole or brown dwarf
Explain evidence that indicated the location of dark matter in galaxies
rotational velocity of stars are expected to decrease as distance from centre of galaxy increases
observed velocity of outer stars is constant
implying large mass on edge which is dark matter
Outline why a hypothesis of dark energy has been developed
data of type 1a supernovae shows inverse expanding at accelerated rate
gravity expected to slow down expansion of universe
dark energy opposes gravity
so universe must be expanding
Outline, with reference with reference to Jeans criterion how Sun is likely to have formed
interstellar gas from earlier supernovae gravitational attraction between particles
if mass is greater than Jean’s criterion
as gas collapses temperature increases leading to nuclear fusion
Suggest how fluctuations of CMB radiation are linked to observation that galaxies collide
fluctuations in CMB due to difference in temperature during inflationary period
leading to formation of galaxies
Show how anisotropies in the CMB distribution are interpreted
CMB anisotropies related to fluctuations in density which are the cause for formation of structures
Describe what is meant by dark matter
invisible
interacts with gravitational force
Explain why rotation curves are evidence for existence of dark matter
rotational velocity of stars expected to decrease outside core of galaxy
flat curve suggests existence of matter that cannot be seen - dark matter
Outline how Hubble’s law is related to z
redshift of galaxies proportional to distance from Earth
Explain the observed galactic redshift in cosmological terms
redshift due to expansion of universe, not recessional speed
expansion of universe increases distance between objects so wavelength increases leading to observed redshift
Explain how observations of spectra from distant galaxies provide evidence that the universe is expanding
all distant galaxies exhibit red shift
Describe the mechanism of formation of type I a supernovae
formed in collision of 2 white dwarf stars where shock waves from collision rip both stars apart
Describe the mechanism of formation of type II supernovae
red supergiant explodes when the core collapses
why type I a supernovae used to measure distances
necessary to measure distance of very distant objects more accurately
act as standard candle
measure apparent brightness
Explain why presence of visible matter cannot account for velocity of stars when r>R
velocity is supposed to decrease
if mass is constant and r is increasing then velocity should be decreasing, however it’s not due to differences in mass
v-r graph is contradicted
r - process
r-process involves «rapid» neutron capture✔
in r-process further neutrons are captured before the beta decay occurs ✔
r-process occurs in type II supernovae ✔
r-process can lead to elements heavier than bismuth/lead/polonium
s - process
s-process involves «slow» neutron capture ✔
in s-process beta decay occurs before another neutron is captured ✔
s-process occurs in giant stars «AGB stars» ✔
s-process terminates at bismuth/lead/polonium
Note
Flashcard