Sky localizations of gravitational-wave signals detected by LIGO beginning in 2015 and, more recently, by the LIGO-Virgo network. Only events in the same hemisphere as GW170817 are shown. The background shows a projection of the Earth's surface. After Virgo came online in August 2017, scientists were better able to localize the gravitational-wave signals, acounting for the dramatically smaller error ellipse for GW170817. [Credit: LIGO/Virgo/NASA/Leo Singer]