Monday, 29 August 2016

N7009: 'planetary' puzzles


Puzzling things planetaries. They mainly emit H-alpha, OIII and H-beta light: i.e. they are almost pure LRGB sources. Here we contrast a superb HST(c) image with the same image made with zero RED and 50% GREEN. This 'recipe' approximates human visual sensitivity. The result is close to what we in fact see in a 10 inch 'scope. Why cant we see red H-alpha in deep-sky objects? Because our Sun emits little in that band and H-alpha is close to the limit of our sensitivity, while we see blue and green quite well. This is why many planetaries look nothing like their big-scope images. 
The central star (inset) was finally seen by 'blinking' with an orange (i.e. minus blue-green) filter, fully blocking the bright nebula but showing the 11.5 mag star.