Ch20 - Cosmology Flashcards
(25 cards)
What does 1 AU represent?
The average distance between the earth and the sun
What is the stellar parallax?
A technique used to determine the distance to stars that are relatively close to the earth, at distances less than 100pc
It relies on the motion of nearby stars against the fixed position of distant stars
Why does the stellar parallax only work with stars of distance less than 100pc from earth?
The angle becomes too small to measure accurately
What is the Doppler effect?
The apparent shift in wavelength which occurs when the source of the wave is moving
What happens to sound waves when the source is moving towards you?
The sound waves are compressed, higher pitch resulting in a decrease in wavelength.
What happens to sound waves when the source is moving away from you?
The sound waves are stretched out, resulting in a increase in wavelength.
What happens to the actual wavelength from the source during the doppler shift?
The actual wavelength remains the same, only the received wavelength is different.
What causes the doppler effect on stars?
The difference in wavelength is due to relative motion between the galaxy and the earth.
What happens when the galaxy is moving towards you?
Absorption lines, wavelength and frequency
Absorption lines are blue-shifted due to a decrease in wavelength and higher frequency. (Shift to the left on spectrum)
What happens when the galaxy is moving away from you?
Absorption lines are red-shifted due to an increase in wavelength and lower frequency. (Shift to the right on spectrum)
What is Hubble’s law?
The recession speed V of a galaxy is proportional to its distance d from earth.
Why may Hubble’s constant may not actually be a constant?
Dark energy is causing the rate of expansion to speed up and distant galaxies are accelerating away.
What tells us that the universe is expanding?
All light we see from galaxies is red-shifted meaning that space is expanding and galaxies are moving away.
What is the cosmological principle (assumption)?
Assumption that when viewed on a large enough scale, the universe is homogenous and isotropic.
What is meant by the universe being homogenous?
The universe has the same composition and properties throughout. Matter is evenly distributed and there are no unique regions.
What is meant by the universe being isotropic?
The universe looks the same in all directions
What are 2 key pieces of evidence supporting the big bang theory?
Hubble’s law and background radiation.
How does Hubble’s law support the big bang theory?
It shows us that the universe is expanding through the red shift of light from distant galaxies.
How does cosmic microwave background radiation support the big bang theory?
Left over heat from the bang is still about and shows up as background radiation. It proves to us that there was once a hot and dense universe, filling the whole universe as the big bang theory says.
What is the assumption made when estimating the age of the universe and why is it poor?
Assumption that the universe has expanded uniformly over time since the big bang. It is poor since the expansion of the universe is expanding.
What is dark energy?
Dark energy acts opposite to gravity pushing space apart. It is a hypothetical form which fills all of space and accelerates expansion making up 68-70% of our universe.
How is dark energy causing the expansion of the universe to accelerate?
Dark energy opposes gravitational pull, pushing outwards. As the universe expands dark energy dominates over gravity making expansion speed up.
