Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2009 May 21



IC 4592: A Blue Horsehead

Credit & Copyright: Rogelio Bernal Andreo

Explanation: This complex of beautiful, dusty reflection nebulae lies in the constellation Scorpius along the plane of our Milky Way Galaxy. Its overall outline suggests a horsehead in profile, though it covers a much larger region than the better known Horsehead Nebula of Orion. The star near the eye of the horse and the center of the 5 degree wide field, is embedded in blue reflection nebula IC 4592 over 400 light-years away. At that distance, the view spans nearly 40 light-years. The horse's gaze seems fixed on Beta Scorpii, also named Graffias, the bright star at the lower left. Toward the top right, near the horse's ear, is another striking bluish reflection nebula, IC 4601. The characteristic blue hue of reflection nebulae is caused by the tendency of interstellar dust to more strongly scatter blue starlight.