Green and blue

Sitting amongst the alien landscape of the harsh Atacama, the antennas of the Large Millimeter/submillimeter Array (ALMA) look eerily otherworldly in this ESO Picture of the Week as they are bathed in a neon green light.

This light is actually an in-built function of ALMA, not evidence of alien activity! The array’s antennas have a flashing green light that blinks periodically whilst the antennas are in operation, and does not disturb the radio-wavelength observations. This light is not usually quite so visible — this picture was captured using a 10-second exposure, during which time a green flash occurred and spread throughout the image, creating a stark contrast between the neon green of the antennas and the deep blue of the night sky.