Several decades ago, astronomers established that distant galaxies are moving away from Earth.
Explain how astronomers can tell that distant galaxies are moving away from Earth.
The graph below shows how the recessional speed of galaxies changes with distance from Earth.
(i) Use the specified data points of (50 Mpc,3600 km/s)(50\text{ Mpc}, 3600\text{ km/s})(50 Mpc,3600 km/s) and (100 Mpc,7200 km/s)(100\text{ Mpc}, 7200\text{ km/s})(100 Mpc,7200 km/s) on the line to show that the speed of a galaxy is proportional to its distance from Earth.
Explain how this relationship provides evidence for the Big Bang theory.
A galaxy is observed at a distance of 75 Mpc75\text{ Mpc}75 Mpc from Earth.
(i) Use the trend in the graph to determine the speed of this galaxy. Give your answer in metres per second (m/s\text{m/s}m/s).
Calculate the time in seconds it takes for a galaxy travelling at this constant speed to travel a distance of 3.15×1024 m3.15 \times 10^{24}\text{ m}3.15×1024 m. Give your answer to 2 significant figures.