The greener objects in the sky
Taken by PAOLO PALMA on October 21, 2025 @
Naples - Italy
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In visual observation of the sky, the colour green has two ‘firsts’: -it is not perceived in stars; -(and yet) it is probably the only shade perceptible in the deep sky objects. There are stars with a peak wavelength in green, but due to how the human eye works, they appear white to us; and I have read and heard of visual observers who have noticed shades tending towards pink in some diffuse nebulae through large-diameter telescopes. But the colour most objectively and widely perceived in non-stellar objects is definitely green, particularly in the planetary nebulae rich in OIII oxygen. Here are some of the most colourful planetary nebulae in the sky: NGC6572, NGC7027 and NGC7009, deliberately photographed tapping the telescope in the form of Ghirigori ( scribbles in italian language), to best capture the shades they show through the eyepiece. The green that characterises them always has a predominance of blue, so we could define it as a "DarkWaterGreen”.
The “greenest” of all is undoubtedly NGC6572, whose colour was noted by Struve when it was discovered in 1825, and which is still known today as the Emerald Nebula. It is followed by NGC7027.Together with Uranus and Neptune, they are among the greenest objects we can admire in visual observation... provided, however, that we do NOT observe them at too high a magnification, in which case their subtle shades suddenly seem to “vanish”.
Dobson telescope 18" and Huawei p30 pro
Photographer's website:
https://www.unsaltonelcielo.it
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