Have you ever seen bright star Sirius flashing and changing colour as it sets below the horizon?
Astrophotographer Paolo Palma has captured the effect in a beautiful video captured on his smartphone.
Sirius is the brightest star that can be seen in the night sky in the northern hemisphere, and is well-known for its ability to apparently change colour as it moves low down and close to the horizon.
This is a phenomena that can also occur with a setting Sun, or even the green flash of the planet Venus.
A low-down full Moon can appear orange, too.
The optical effect is to do with light from a low-down celestial object passing through a thicker part of Earth's atmosphere on its way to our retinas and cameras.
The light is scattered by the atmosphere and so the object seems to change colour.
Sirius's twinkling and colour-changing is a known phenomenon, and astrophotographer Paolo Palma has managed to capture a video showing the effect of this via his smartphone camera.
How the Sirius green flash was captured
Paolo describes the video and accompanying composite image, captured on 11 May 2024, as "the green ray of the brightest star in the sky."
"Around mid-May, Sirius reaches the western horizon and sets in the twilight lights, " he says.
"This is the best time to try to admire its 'sunset' and the play of colour it creates with the atmosphere in a still, bright context.
"I captured this video through a 12-inch Dobsonian telescope as Sirius set, less than 4° from the horizon, next to a pine tree more than 1.6km away from my observation point.
"The video was taken using a Huawei p30 Pro smartphone, and the image collage was made using frames from that video."
See more of Paolo's work via his website www.unsaltonelcielo.it and his Instagram profile @unsaltonelcielo
