Light at Night

It’s difficult to believe that this photo was captured at nightime. The impressive peak of Maunakea — the dormant volcano that houses Gemini North, of the international Gemini Observatory, a Program of NSF’s NOIRLab — appears to be clearly lit under a bright blue sky. Shadows are even visible between the dormant volcano’s cracks and crevices. 

There are two clues that this image was actually taken at nighttime. First, the bright streaks in the sky are actually star trails — streaks of starlight, which appear when a photographer uses a long exposure. They are due to the Earth’s rotation on its own axis. The second clue is subtler. In the bottom left corner of the image, artificial lights can be seen. These lights would not be required in daytime. The overall brightness of the image is caused by such a long exposure time, so the camera had time to collect a lot of starlight and moonlight, creating an image that appears to be Sun-drenched!