LIGO operates two gravitational-wave observatories in unison, located 3,002 km (1,865 mi) apart: the LIGO Livingston Observatory (30°33′46.42″N 90°46′27.27″W ﻿ / ﻿ 30.5628944°N 90.7742417°W ﻿ / 30.5628944; -90.7742417) in Livingston, Louisiana, and the LIGO Hanford Observatory, on the DOE Hanford Site (46°27′18.52″N 119°24′27.56″W ﻿ / ﻿ 46.4551444°N 119.4076556°W ﻿ / 46.4551444; -119.4076556) near Richland, Washington. The tiny shifts in the length of their arms are continually compared and significant patterns which appear to arise synchronously are followed up to determine whether a gravitational wave may have been detected or if some other cause was responsible.