The enigmatic nebulae range from compact planetary forms to disperse gaseous clouds and reflection nebulae. Colors reveal the chemistry of the gases, with red the main emission of ionized H-alpha (656 nm), blues mainly doubly-ionized O (~500 nm), and for reflection nebula blue from light scattering.
Astrophotography by Rex A Parker PhD. Astronomy from my Home Observatory (New Jersey USA); and Star Shadows Remote Observatory (Cerro Tololo Chile, PROMPT2, UNC-Chapel Hill). -- For my blog, click 3-bar icon at right (News).