Nebulae
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 ... Data are mostly from my home observatory in New Jersey USA; also from Star Shadows Remote Observatory at CTIO Chile, PROMPT2 telescope - thanks to Steve Mazlin, also Dan Reichardt, UNC-Chapel Hill; and from Mt Lemmon Sky Center, AZ - thanks to Adam Block.