Object name: M078

Designation(s): M078, MCNEILS NEBULA,

M78 is a reflection nebula in Orion. Much of the constellation is full of dust and gas. If one or more super hot star with strong ultraviolet light is around the gas will be ionized. This will cause the hydrogen to glow with a characteristic red color and oxygen to give off a weaker teal green color while some hydrogen gives off a blue color. The red hydrogen dominates causing such nebula to glow a pink color in color images but be green when seen visually in a scope that makes the nebula bright enough to activate the color cones in the human eye. So why aren't they red? Seems the eye is far more sensitive to the teal and blue colors than the very deep red of hydrogen alpha so the eye sees mainly the oxygen while cameras with good red sensitivity (most DSLR cameras block deep red unless modified) will see it as red-pink in color.

Reflection nebula, however, behave differently from emission nebula. Their color depends on the color of the star and its location. If the star is in front of the nebula lighting it like a lamp lights a wall the nebula will take on the color of the star. If it is inside the nebula or behind it, the dust and gas scatter the blue light of the star, no matter what color the star. This then tends to make the nebula blue. If the illuminating star is blue then the color will usually be a vivid blue. The cooler and thus redder the star the less blue dominates. In this case, the stars appear to be in and behind the nebula and are all somewhat to very blue. This causes the nebula to be rather white in areas and blue in others depending on the size of the dust particles and which stars best illuminate which part of the nebula.

Like most of the dust and gas in Orion, it is about 1500 light-years distant. It was discovered by Pierre Méchain in March of 1780. The exact date is unknown. He later communicated his find to Messier who recorded it on December 17, 1780. I can't find that Messier ever actually looked at this one. It appears he took Pierre Méchain's word for it.

Southwest of M78 toward the lower right of my image is McNeil's Nebula. This nebula was discovered on January 23, 2004 by Jay McNeil. Some sources incorrectly say February. Later a prediscovery image was found taken in October 1966 by Evered Kreimer while he was taking M78 for a book on the Messier objects. Later after McNeil's discovery when it was lost in the sun's glare it vanished. Finally, in the fall of 2008, it reappeared and has been constantly visible ever since. Most think this was due to the star's brightness change as it is a protostar just starting to shine. Either it flashed for a bit then faded or had temporarily broken out of its birth cloud of dust and gas when first Kreimer then McNeil happened to catch it. Since 2008 both star and nebula are shining rather unchanged from the several years of images I've taken of this field. Will it disappear again? Maybe but I suspect it either blew the dust shroud away or has finally stabilized enough to give a rather constant light. Protostars can be quite unpredictable so changes are still possible. I intend to keep looking at least.

For more on both of these see:

14" LX200R @ f/10 L=4x10' RGB=2x10', STL-11000XM, Paramount ME