The blue hour

This panorama of the landscape around ESO’s Paranal Observatory, located in the Chilean Atacama Desert, was taken by ESO Photo Ambassador Petr Horálek. Captured at dusk, it shows the moment just after sunset, when the the sky is painted in beautiful colours of yellow, orange, red, even blue-purple, and the reddish hues of the desert below are enhanced by the soft light. This time of day is known as twilight, but is also referred to as the blue hour (named for the colour of the sky). The unique and ethereal quality of the light during blue hour has also earned it the nickname of “sweet light” amongst artists and photographers. The planet Venus stands out against the pink of the sky in the very centre of the image, while the Very Large Telescope (VLT) rests atop the mountain on the right, Cerro Paranal. The Andromeda Galaxy is faintly visible to the right of the four giant 8.2-metre-diameter VLT Unit Telescopes, recognisable by its iconic oval shape. Andromeda is a Northern sky object, barely visible above the safety pointing limits of the telescopes at Paranal.