Astronomy Picture of the Day—20180802

Discoverthe cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2018 August 2

TheIris Nebula in a Field of Dust

ImageCredit & Copyright: Franco Sgueglia & Francesco Sferlazza

Explanation:What blue flower grows in this field of dark interstellar dust? The IrisNebula. The striking blue color of the Iris Nebula is created by light from thebright star SAO 19158 reflecting off of a dense patch of normally dark dust.Not only is the star itself mostly blue, but blue light from the star is preferentially reflected by the dust -- the same affect that makes Earth's skyblue. The brown tint of the pervasive dust comes partly from photoluminescence-- dust converting ultraviolet radiation to red light. Cataloged as NGC 7023,the Iris Nebula is studied frequently because of the unusual prevalence thereof Polycyclic Aromatic Hydrocarbons (PAHs), complex molecules that are alsoreleased on Earth during the incomplete combustion of wood fires. The brightblue portion of the Iris Nebula spans about six light years. The Iris Nebula,pictured here, lies about 1300 light years distant and can be found with asmall telescope toward the constellation of Cepheus.