The Expanding Universe Flashcards
Explain how radar is used to calculate distance
Transmit radar signal towards planet or moon. Wait for bounced signal to return. D=ct/2
What are the primary limitations of radar?
•time
•energy
What is the limitation of parallax to measure distance?
Beyond Milky Way
What is a cepheid?
Young bright star type found to pulsate
What are arguments for spiral nebulae being clouds within Milky Way rather than distant galaxies about the same size?
•pinwheel galaxy observed to rotate over course of years- if it was as big as mw it would have to be rotating faster than light
•andromeda would have to be ludicrously far away to be the size of the Milky Way
•one nova in andromeda outshone the rest/ how could one star be brighter than billions of others
What are arguments for spiral nebulae being distant galaxies about the same size rather than clouds within the Milky Way?
•why would there be as many novae in one tiny cloud as in the rest of the mw
•dark lanes in nebulae looks very like dust in mw
What does hubbles law imply?
That universe is expanding
Do galaxies get larger?
No
On average are galaxies moving?
No, space between them is expanding
Describe expansion of space between galaxies
•space internally getting larger
•stretches light on its path
•uniform;there is no centre
What happens to gravitationally bound objects when galaxies move apart?
Not pulled apart
What are baryon acoustic oscillations?
Pattern of matter in the universe has a distinctive scale. Distance sound travelled in the early universe persists as an imprint across cosmic time. Same scale except for cosmic expansion. Tells us size at given redshift
What is standard candles?
Luminosity distance. Assuming light spreads like 1/d^2
