Why one square kilometre?
Increasing a telescope’s collecting area increases its sensitivity. Thanks to higher sensitivity, weaker signals emitted by more distant or fainter celestial objects, can be received. One of the aims of the SKA is to receive signals from the early Universe (the most distant objects that can be observed). These signals are very faint and hence require a very sensitive telescope so they can be detected. This means the SKA needs to be very large.
