A Global Astronomy Event.

 A map of the approximately 70 light-based observatories that detected the gravitational-wave event called GW170817. On 17 August 2017, the LIGO and Virgo detectors spotted gravitational waves from two colliding neutron stars. Light-based telescopes around the globe observed the aftermath of the collision in the hours, days, and weeks following. They helped pinpoint the location of the neutron stars and identified signs of heavy elements, such as gold, in the collision's ejected material. [Credit: LIGO-Virgo]