March 29, 2010
The photo above is a long exposure of the star field above the peaceful Albufeira Lagoon (Lagoa de Albufeira), in southern Portugal. The total exposure time was 80 minutes; starting at 10:26 p.m. on March 12, 2010 and ending at 11:56 p.m.
Each curvilinear streak is the path of a star. On this early spring night, the paths of numerous stars can be clearly seen; including Procyon in Canis Minor, Aldebaran in Taurus, the Pleiades cluster, Sirius in Canis Major, and both Betelgeuse and Rigel in Orion. Of special interest; however, are the star tracks reflected in the lagoon. With just the slightest murmur of a breeze the water stirred, blurring the tracks and saturating the colors. Sirius, the brightest star visible in the night sky, produces the most obvious streak. Its blue-white appearance is indicative of its very hot surface temperature; approximately 10,000 degrees K. For comparison the temperature of the Sun is approximately 6,000 degrees K. Note that only the brightest first magnitude stars are reflected in the water. Stars of lesser brightness simply aren’t brilliant enough to be reflected off water surfaces. Additionally, even the brightest stars have rather feeble reflections if they’re situated overhead rather than lower in the sky. The Atlantic Ocean is behind the sand embankment in the background.
Photo details: To record the motion of the stars, I registered the 159 images taken with my Canon 50D camera; each one has a 30 second exposure; aperture f/4; ISO 1000; Sigma HSM EX 10 mm lens. Later, I combined all of these images manually in Photoshop CS3 to produce a single image.