Tuesday 8 March 2016

The Sword of Orion... in colour!

As I already explained in an earlier post, there's so much colour to be seen in the dark, nightly sky, much more than we can possibly imagine. The object just needs to be bright enough to reveal it to our inadequate human eyes. Now it so happens that there's an incredibly bright nebula out there... an object of such rare beauty and complexity that it'll leave you dazzled, even when you're looking at it for the millionth time: the Orion Nebula (also see here). If you've got a sufficiently large telescope, let's say with a diameter of about 8" and up, this nebula will reveal the same greenish-blue hue of the Eskimo Nebula (see here) but possibly even stronger and all across its brighter parts and filaments. You'll remember that this colour indicates a large presence of hydrogen and oxygen in the nebula and per chance this is also the colour we perceive most easily in the dark. 

Red, on the other hand, is the colour which is most difficult to make out, although if you look at photographs from various nebulae it's often the most prominent tone. That's because also red indicates the presence of hydrogen, which evidently is the most abundant element in our universe. But as far as my personal experience goes (limited to the northern hemisphere), apart from stars which are point light sources, no extended or diffuse object has ever been bright enough to reveal red to my eyes. There's one exception however... the mighty Orion Nebula! I made this observation with my good old 18" Dobsonian under not really ideal conditions. I remember that the sky's transparency wasn't all that great and my eyepieces were constantly fogging up due to the humidity in the air. But I did see it! Right along the brightest borders of the nebula I noticed a reddish-orangy hue, contrasting nicely with the blue-green of the rest. I couldn't use a nebula filter to make the nebula stand out more against the background because these filters actually block all frequencies of light apart from blue-green. So many details within the nebula weren't quite as visible as they could have been with the use of a filter. But that would have destroyed the reddish tint on its edges, which after all was the goal of this observation. Yet I was incredibly happy because I'd seen it. 

Observing the night's sky is often a work of patience and allowing yourself to adjust to the image. Take your time and never be too hasty or you may miss some exciting details that only reveal themselves after a couple of minutes. If your observation spot isn't completely immersed in darkness, it'll also help to use a hood of some kind to prevent stray light from entering your eyes. You should only see pitch black around you, apart from the field of view of your instrument. Relax. Sit down comfortably. And then... let it all come to you. It will!


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