Computer displaying three pulsars
Pulsar triangulation was a manner of navigation whereby pulsar frequencies and their geographic light year measurements were used to identify a specific location in space.
In 2153, while Phlox was briefly connected to the Borg collective consciousness, he was able to detect a specific set of numbers being repeatedly transmitted to the Delta Quadrant. Feeding the numbers into Enterprise's computer, the numbers were revealed to be the spatial coordinates of Earth, suggesting a future invasion – though not for another two hundred years. (ENT: "Regeneration")