M78 (diffuse nebula in Orion)
460: M78 image
M78 is the brightest diffuse reflection nebula in the sky. It belongs to the Orion complex, a large cloud of gas and dust centered on the Orion Nebula M42/M43, and is about 1,600 light years distant. M78 was discovered by Pierre Méchain at the beginning of 1780, and subsequently logged by Messier on December 17, 1780.
Visually, M78 appears more comet-like than any of Messier’s other objects. It is barely visible as a small dim patch in binoculars or a short-tube refractor under dark, clear conditions. The Astronomical League rates M78 as a “Tougher” object with 7X50 binoculars, but I think that’s a bit optimistic for Bullington. I have bagged M78 once or twice from Bullington with binoculars, but doing so required averted vision and is hopeless on any but the darkest, clearest nights.
In a 6” or larger scope, M78 appears as a bright patch of nebulosity, with the two tenth-magnitude illuminating stars appearing as a double nucleus. M78 is actually just the brightest portion of a huge cloud which also includes the nearby NGC 2071, shown at the lower right, NGC 2067, and NGC 2064. I have gotten NGC 2071 in our 10” Dob at Bullington under very good conditions, but the latter two are so dim that I’ve never been able to see them despite knowing exactly where they should appear.
470: M78 with Telrad
Getting M78 into your scope’s field of view is pretty straightforward. Place your Telrad as shown, with Alnitak and Alnilam just on the edge of the 4-degree circle, and then nudge the scope about 1 degree or a quarter of a Telrad field in the direction shown to center M78 in your eyepiece. M78 should appear in your low-power eyepiece as a relatively bright hazy patch. Its extent is about 8 X 6 arcminutes or roughly a quarter the diameter of the full moon, so it’s small enough to need some power to reveal its details. Fortunately, it’s also bright enough to take reasonably high power. We generally use an eyepiece that yields 125X or so to put M78 in context with its surroundings.