Red-shift Flashcards
All 18 cards in this deck
What is meant by red-shift?
The observed increase in wavelength of light from galaxies as they move away from us.
Which feature of a galaxy's visible light spectrum is used to measure its red-shift?
The pattern of dark (absorption) lines — in a red-shifted galaxy the whole pattern is shifted towards the red (longer wavelength) end.
What are the steps to compare two galaxies using their light spectra?
e.g. galaxy A's dark lines are shifted further towards the red end than galaxy B's
- Compare the shift of the dark lines: A has the greater red-shift.
- Greater red-shift means faster recession: A is moving away from us faster than B.
- Faster recession means greater distance: A is further away from us than B.
How does the speed at which a distant galaxy is moving away from Earth depend on its distance from Earth?
The further away the galaxy, the faster it is moving away, and so the bigger the observed increase in wavelength.
True or false? Red-shift means the wavelength of light received from a galaxy has decreased.
False. Red-shift is an observed increase in wavelength, because the galaxy is moving away from us.
What does the red-shift observed in light from most distant galaxies provide evidence for?
That space itself (the universe) is expanding.
What does the Big Bang theory suggest about how the universe began?
The universe began from a very small region that was extremely hot and dense.
How does red-shift evidence support the Big Bang theory?
The furthest galaxies are moving away the fastest, which suggests that at some time all the galaxies/matter started at the same point.
What do observations of supernovae made since 1998 suggest about distant galaxies?
That distant galaxies are receding (moving away) ever faster — the expansion is accelerating.
Give the reason why scientists sometimes have to change their theories about the universe.
There are new observations or evidence that do not fit the current theory or model.
How do scientists arrive at a theory such as the Big Bang theory?
They make observations (e.g. the red-shift of galaxies) and develop a model that explains them, then test it against further observations.
True or false? Red-shift of galaxies in every direction shows that the Earth is at the centre of the universe.
False. It shows that space itself is expanding everywhere, so all galaxies move apart from each other.
Give two examples of things about the universe that scientists still do not understand.
Dark mass (dark matter) and dark energy.
What is dark energy?
Something not yet understood that is thought to cause the expansion of the universe to accelerate.
What is dark mass (dark matter)?
Mass in the universe that cannot be seen and is not understood, detected only through its gravitational effects.
Which observations led scientists to suggest that dark energy exists?
Observations of supernovae since 1998, showing that distant galaxies are receding ever faster.
True or false? Scientists now understand everything about what the universe is made of.
False. There is still much that is not understood, for example dark mass and dark energy.
True or false? The bigger the observed red-shift of a galaxy, the further away from us that galaxy is.
True. Greater red-shift means a faster speed of recession, and the fastest-receding galaxies are the most distant.