P8.3 - Beyond Earth Flashcards
What is the difference between an absorption spectrum and an emission spectrum?
Absorption spectrum - A continuous spectrum with dark lines corresponding to particular frequencies being absorbed by an atom.
Emission spectrum - A set of frequencies of radiation emitted by an atom when excited electrons move to lower energy levels.
What is the Doppler effect?
The physical phenomena by which there is a change in the observed frequency/wavelength of wave, due to relative motion between observer and source.
Relative motion - Source moving, OR observer moving, OR both source and observer moving.
What happens, in terms of the Doppler effect, when a sound source moves towards you?
When the sound source moves towards you, wave peaks move closer together, the wavelength decreases and the observed frequency/pitch of sound increases.
What happens, in terms of the Doppler effect, when a sound source moves away from you?
When the sound source moves away from you, wave peaks move further apart, the wavelength increases and the observed frequency/pitch of sound decreases.
Why is the the Doppler effect with light waves very difficult to observe?
The light waves have a much smaller wavelength than sound waves.
The Doppler effect is observed when the relative motion between the observer and the source is very large.
What is red-shift and what does it imply?
Red shift - The shift in wavelength of the light emitted from a source to longer wavelengths.
Implies - That the source is moving away from us.
What is blue shift and what does it imply?
Blue shift - The shift in wavelength of the light emitted from a source to shorter wavelengths.
Implies - That the source is moving towards us.
Describe how the red-shift of distant galaxies provides some evidence for the The Big Bang Theory.
OBSERVATIONS
Light from distant galaxies is red-shifted.
The further away the galaxy, the greater the red-shift.
CONCLUSIONS
Galaxies are moving away from us.
The further away the galaxy, the faster it is moving away.
Thus, if galaxies are moving away from each other, this suggests that at one point, all matter must have existed at a single point in space - One piece of evidence for the big bang.
How do we know light from distant galaxies are red shifted?
The absorption spectra of stars contain black lines.
These black lines correspond to very specific wavelengths of light absorbed by certain atoms in the star.
Hence, all spectra from starts contain a series of very specific black lines (distinct pattern of separated lines).
These black lines are seen shifted in the spectra from distant stars towards longer wavelengths.
This implies that light from distant stars have undergone a Doppler shift.
Describe how cosmic microwave background radiation provided evidence for the Big Bang theory.
At the beginning of the universe, all the energy of the universe would have manifested as very short wavelength gamma waves.
As the universe expanded, this gamma radiation would have stretched out to longer and longer wavelengths… and is now microwave radiation.
The fact that the microwaves uniformly/evenly fill the universe suggests they all started off from a single point (filling the universe as the universe expanded).
The steady state theory cannot explain this fact, only the Big Bang Theory can.
What is/are: The sun Planets Moons Minor planets Comets
The sun - Star at the centre of the solar system.
Planets - Spherical bodies that orbit the sun.
Moons - Spherical bodies that orbit planets.
Minor planets - Small spherical objects that orbit the sun.
Comets - Objects made of dust/ice that orbit the Sun with long period, elliptical orbits.
What are the inner planets and what are they made of?
Mercury - Atmosphere very thin, no moon
Venus - Atmosphere is mainly carbon dioxide and it rains sulfuric acid, no moon
Earth - One moon
Mars - Atmosphere very thin, two moons
- Rocky
- All have an atmosphere
What are the inner planets and their properties?
Gas giants - Jupiter and Saturn
Ice giants - Uranus and Neptune
All have rings and a lot of moons.
What is between Mars and Jupiter?
An asteroid belt - A band of dust and larger pieces of rock left over from the formation of the solar system and orbits the sun.
Describe the beginning of the life cycle for all stars.
- Dust and gas gather under gravity to form a protostar.
- Once the protostar has become hot and dense enough, nuclear fusion begins and the star becomes a main sequence star.
Describe the middle stages in the life cycle for all stars.
- A star is stable during its main sequence.
- The radiation pressure outwards from nuclear fusion balances the gravitational attraction inwards (there is equilibrium/stability).
- Eventually, the hydrogen nuclei will run out.
- The star will cool, and its radiation pressure drops.
- The gravitational force collapses the star, causing it to heat up again.
- The fusion of heavier elements begins.
- The energy from fusion increases. Therefore, the radiation pressure increases. The star becomes either a red giant or a red super giant.
What is the ending steps for the life cycle of a small star (a red giant)?
- The nuclei for fusion run out.
- Fusion slows down.
- Radiation pressure decreases.
- The gravitational force collapses star.
- The star heats up becomes a white dwarf.
- The star eventually cools down to form a black dwarf.
What is the ending steps for the life cycle of a large star (a red super giant)?
- Lots of heavier nuclei fused together to release lots of energy.
- There is a large increase in radiation pressure outwards. This is much larger than the gravitational pull inwards.
- The star explodes in a supernova.
- A very dense neutron star forms.
- If the neutron star is very dense, it could become a black hole.
What is the life cycle for a low mass star?
Protostar - Main sequence star - Red giant - White dwarf - Black dwarf
What is the life cycle for a high mass star?
Protostar - Main sequence star - Red super giant - Supernova - Neutron star - If these is a very high density - Black hole
Explain why the sun started to shine.
Once the sun became hot and dense enough under gravity, nuclear fusion of nuclei began, releasing energy, causing the sun to emit EM radiation and shine.
Explain why the sun is not expanding?
There is a balance between the force of gravity inwards and the radiation pressure from nuclear fusion outwards, that ensures the sun does not expand or contract.
