Details Satellites in polar orbits usually travel past Earth from north to south rather than from west to east, passing roughly over Earth's poles. Satellites in a polar orbit do not have to pass the North and South Pole precisely; even a deviation within 20 to 30 degrees is still classed as a polar orbit.

Question (a) Calculate the approximate age of the universe from the average value of the Hubble constant, H_0 = 20\textrm { km/s}\cdot\textrm {Mly} H 0 = 20 km/s⋅ Mly . To do this, calculate the time it would take to travel 1 Mly at a constant expansion rate of 20 km/s.