Space Flashcards
Define Luminosity
The rate at which energy of all types is radiated by an object in all directions. (Power)
What is a Black Body Radiator?
Theoretical perfect emitter. Absorbs and emits all wavelengths of the EM spectrum.
Define Stefan-Boltzmann Law
Output power from a black body is proportional to its surface area and fourth power of temp in kelvin.
State Stefan-Boltzmann’s Equation
L = σAT ^4
σ = 5.67×10^-8 W m^−2 K^−4
Define Wien’s Law
The relationship between peak output wavelength and temp for a black body.
λmaxT = 2.898 × 10^−3 m K
1 astronomical unit is
the radius of the earths orbit around the sun.
1 AU = 1.5x10^11m
1 Light Year is
The distance light can travel in 1 year
1 LY = 3x10^8 x 365 x 24 x 60 x 60 = 9.46x10^15m
1 Parsec is
the distance a star must be from the sun in order for the parallax angle to be 1 arcsecond.
1pc = 3.09 x10^16m
Trigonometric Parallax
is a method for measuring distance to close stars, by measuring angle at 6 month intervals.
Define Standard Candle
stars with a known luminosity
Intensity =
Luminosity/Area (Wm^-2)
What is the Doppler Effect?
The relative motion between an observer and moving body, causes a change in observed wavelength and frequency.
Define Red Shift
The shift in wavelength of a stars separation caused by star moving away from the Earth.
Define Hubble’s Law
The recession velocity of a galaxy is directly proportional to the distance to it.
v = Hod
Ho=2.29x10^18ms^-1
Derive an equation that gives the age of the universe
v=Hod v=d/t
d/t=Hod
Ho=1/t
1/2.29x10^18 = 4.36x10^17s
Explain the life cycle of a low mass star
Protostar - Main Sequence Star - Red Giant - Planetary Nebula - White Dwarf
Explain the life cycle of a Massive Star
Protostar - Blue Supergiant - Red Supergiant - Type 2 Supernova - Black hole or Neutron Star
How is a Protostar formed?
Clouds of dust and gas (nebula), collapse under gravity.
The next stage after protostar:
Protostar contracts and heats up, until hydrogen nuclei fuse together to form helium. This creates enough radiation pressure to prevent gravitational collapse. Protostar turns into main sequence star.
After main sequence star:
Red Giants form when core runs out of hydrogen, nuclear fusion stops and outwards pressure stops. Helium core contracts and heats up under weight of star.
After Red Giant:
Low mass stars form white dwarfs - helium is fused and star collapses under gravity. Outer layer is ejected as planetary nebula, leaving hot dense core.
After Red Supergiant:
High mass stars keep fusing elements until core is made up of iron. Star explodes in type 2 supernova leaving neutron star or black hole.
Big Crunch occurs when:
Density of universe is greater than the critical density. Gravity is strong enough to stop expansion and start the universe contracting again.
Define Open Universe
Critical density is greater than density of the universe, gravity is too weak to stop expansion and the universe keeps expanding forever.
How can a stars size be determined?
Temperature found using Wien’s Law. Luminosity is found from H-R diagram. r is calculated using Stephan’s Law.
Describe how velocity of galaxies may be determined?
Measure wavelength of light from the galaxy and compare it to the wavelength for a source on Earth. v is found from: Δλ/λ ≈ v/c
Explain what is meant by a
Doppler shift and how it is used to deduce the motion of distant galaxies
Doppler shift is the change in frequency and wavelength due to the motion of the source. The shift of a spectral line can be used to find v. Red shift shows the galaxy is receding.
What is a line spectrum?
A series of lines on a dark background.
Explain the meaning of a red shift.
Change in wavelength of the light. Wavelength increases and frequency decreases.
What is meant by the Doppler effect (electromagnetic Doppler effect) when applied to light?
Change in wavelength/ frequency due to the relative motion between an observer and source.
Edwin Hubble reached a number of conclusions as a result of observations and
measurements of red-shift. State two of these conclusions.
Recession velocity is proportional to galaxy distance. Red shift is due to a galaxy moving away.
What is meant by the critical density of the Universe?
Density is large enough to prevent Universe expanding forever but not to big to cause contraction of the universe.
Explain how the inflation of the balloon can be used to model the expansion of the
Universe
Dots represent galaxies. Balloon inflation represents expanding Universe. Dots further apart move apart faster, as with galaxies.
Discuss the ultimate fate of the Universe and the reason why the fate of the Universe is uncertain.
Universe may continue to expand or may collapse back on itself. Fate depends on mass of universe. Since mass determines force on moving stars. So far, not enough mass has been found to stop expansion. There may be undetectable matter present - neutrinos, very hard to detect.
Explain how the nuclear processes within the Sun are able to release energy
Nuclear fusion - Hydrogen nuclei is being fused to form helium. Mass loss is converted to energy.
∆E =∆mc^2
The huge power output of the Sun is due to nuclear fusion reactions taking place within
its core. State and explain the conditions necessary for fusion to occur.
High temperature and pressure to overcome electrostatic repulsion. Nuclei come close enough to fuse/for strong (nuclear) force to act. Causing high collision rate.
Explain what is meant by the term red shift in this context and state the inference that Hubble made from his measurements.
The observed wavelength is stretched out. The universe is expanding. The (recessional) velocity of galaxies is proportional to distance. All distant galaxies are moving apart.
Explain how the ultimate fate of the Universe is associated with the Hubble constant
fate of universe depends on the density of the universe. Hubble “constant” is changing due to gravitational forces
How does a white dwarf differ from the Sun?
White dwarf is hotter and has a lower luminosity. No fusion in the core. More dense and smaller.
What is the future of the white dwarf?
Temp decreases and luminosity decreases.
A key property of dark matter is that it
emits no detectable electromagnetic-radiation
Explain how standard candles are used in astronomy and how a layer of dust around a Cepheid may affect conclusions
Standard candle are objects of known luminosity. Flux is measured on Earth. F=L/4πd^2 used to calculate distance to standard candle. Dust layer will reduce brightness of Cepheid, so it will appear further away than it is.
Describe how astronomers would have determined the velocity of each galaxy
Measure wavelength of light from the galaxy and compare it to the wavelength for a source on Earth. V is found from fractional change in wavelength equals ratio of speed of source to speed of light. Δλ/λ = v/c
Scientists are uncertain about the fate of the universe. Explain Why.
Due to difficulty in making accurate measurements of distances to galaxies. Hubble’s Constant has a large uncertainty because of the existence of dark matter. Values of average density of universe have a large uncertainty, hence so does critical density measurements. Dark energy may mean we don’t understand gravity as well as we thought, so hard to predict how gravity will determine fate.
Explain what is meant by the term red shift
The observed wavelength is longer than the actual wavelength. The universe is expanding. All distant galaxies are moving apart. The recessional velocity of galaxies is proportional to distance
Explain how astronomers calculate the sizes of these stars using information from H-R diagram
Temp found from Wiens Law. λmaxT = 2.898 × 10^−3 m K.
Luminosity found from HR. Stefan’s Law used to find r.
Explain how redshift can be used to determine the velocity of a galaxy relative to
the Earth.
Measure wavelength of light from galaxy. Compare wavelength to wavelength for a source on Earth. Use redshift formula to calculate velocity.
Describe how you would expect the average density of matter in the universe to
affect its ultimate fate.
- If density less than critical value, expansion would continue for ever.
- If density is greater than critical value, expansion would stop and universe would contract again.
- If density equals critical value, expansion rate would decrease to zero but universe would not contract again.
It is difficult for scientists to estimate the average density of the universe reliably.
Explain why.
Amount of dark matter present in uncertain, as dark matter does not interact via electromagnetic interactions. Value of Hubble’s Constant in uncertain - measurements of distances to distant galaxies are uncertain.
Describe how distances too large for the use of standard candles can be determined
Measure change in wavelength and use this to calculate relative velocity using red shift formula. Then apply v=Hod.
Use the binding energy per nucleon curve to explain how fusion and fission both
release energy
Fusion involves increasing binding energy per nucleon as nucleon number decrease.
-Fission involves increasing binding energy per nucleon as nucleon number decreases
-If binding energy per nucleon increases, energy is
released in the process
