For Chilean astrophotographer Osvaldo Castillo, the night sky above the European Southern Observatory‘s (ESO) Paranal Observatory held a breathtaking sight.

“I couldn’t believe I was photographing a circumpolar startrail in Paranal; without a doubt, one of the most incredible experiences I’ve had as a photographer,” said Castillo in a recent ESO article.

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Star trails are the visible imprint of Earth’s rotation. As our planet spins around its axis, the stars appear to sweep across the sky in long, circular arcs. When a camera takes repeated long-exposure images over hours and the frames are later stacked together, these arcs become luminous trails revealing the circular (apparent) path of the stars.

The exact pattern depends on where the photographer is located on Earth. In the Southern Hemisphere, the stars appear to circle the south celestial pole, an extension of Earth’s south rotational axis into the sky. In Castillo’s photograph, that pole forms the central point around which every trail curves.

Earth’s rotation helps create vivid star trails in long exposure images. (Image credit: O. Castillo/ESO)

in a statement. “Fortunately, the calculation and orientation to the South were accurate.” The payoff is evident: a gorgeously composed starwheel set against one of the world’s premier astronomical sites.

Paranal observatory and astrophotography.