... Dark Markings of the Sky . ... Credit: Steve Cannistra ( StarryWonders ) Explanation: Based on wide field photographs, American astronomer Edward Emerson Barnard cataloged the dark markings of the sky in the early 20th century. Barnard's markings are dark nebulae, interstellar clouds of obscuring gas and dust. ... Typically a light-year or so across, many of Barnard's dark nebulae are themselves likely sites of future star formation. ... Publications with keywords: dark nebula . ...