[mturmon]

The wording is misleading. You need to compute the angle of incidence of the incoming wavefront to a high accuracy in order to localize the source.

The key quantity is not the absolute delay introduced by the absolute distance from antenna to antenna (which is tens of meters, http://www.atnf.csiro.au/projects/askap/ska.html). It's the differential delay as a function of incidence angle.

[mikeash]

Ah yes. The difference in arrival time was many nanoseconds but it needed to be measured to within a fraction of a nanosecond to accurately localize the source.