Introduction: A night to remember over Paranal
On November 25, 2025, the night sky above ESO’s Paranal Observatory in Chile treated observers to a rare celestial procession. A Chilean astrophotographer, Osvaldo Castillo, captured star trails that curved and looped across the dome of the Very Large Telescope (VLT) complex, revealing the movement of stars in a circumpolar pattern around the celestial pole. The image, chosen as a photo of the day, showcased not only technical skill but the quiet drama of the Atacama Desert under a pristine southern sky.
What makes this shot special: circumpolar star trails
Star trails are created by the long exposure of a fixed camera as the Earth rotates. When the sky is rich with bright stars near the north or south celestial poles, trails wrap around the pole in elegant circles. In Paranal’s southern hemisphere location, the circumpolar motion is a perpetual reminder of our planet’s rotation and the intimate connection between ground-based observatories and the cosmos. Castillo’s framing captures a near-circular arc that hints at the rotation of the heavens, with the telescope serving as a grounded centerpiece in a sea of streaking starlight.
Technical notes that elevate the image
To render a circumpolar startrail with a telescope silhouette in the foreground requires careful planning. The exposure length must balance bright star trails with the visibility of the telescope and its environment. A sequence of shorter exposures, later stacked, can minimize noise and maximize the smoothness of the arcs. Castillo’s choice of composition—placing the telescope slightly off-center—adds depth and a sense of scale, allowing viewers to feel the telescope as a witness to the sky’s motion rather than simply a structure in the desert.
The photographer and the place: Paranal’s unique backdrop
Paranal Observatory sits in a remote stretch of the Atacama Desert, where dry air and high elevation yield some of the clearest skies on Earth. The location is favored by astronomers for cutting-edge research and by photographers for night-sky portraits that combine architectural form with astronomical spectacle. Osvaldo Castillo, known in Chile’s astrophotography circles for his patient, precise landscapes, used the stark geometry of the VLT’s architecture to anchor the starry ribbons above. The resulting image pays tribute to the collaboration between humans who explore the universe and the landscapes that frame their work.
A day in the life of a night sky photo
While technical prowess is essential, the artistry of a night-sky image rests on timing, weather, and a bit of serendipity. In this November evening, stable atmospheric conditions and a clear, dark horizon granted Castillo a window to chronicle the sky’s slow motion. The photograph becomes more than a pretty picture; it is a narrative of patience, light, and the patience of craftsmanship. The star trails, glowing with a cool, celestial blue, contrast against the warm hues of the desert floor and the hard lines of the telescope, creating a visual dialogue between nature and science.
Why this matters to the astronomy community
Photo-of-the-day picks like this illuminate the human side of astronomy—how scientists and enthusiasts live with the night, and how imagery can inspire the next generation of skywatchers. The Paranal image demonstrates that even routine celestial motion can yield extraordinary visual stories when viewed through a skilled lens. It also reinforces the sense of pride that Chilean astrophotographers bring to global audiences, highlighting the country’s role as a steward of some of the world’s most important astronomical facilities.
