[ngcles]

Hi Trav & All,

I'm not surprised by your report at all Trav. I could certainly see lime green colouration in M42 with my old 8" with no difficullty 15-20 years ago when I was in my 30s. It was as you say easy to see at low power and even in a suburban site with a ZLM about +4.9. Less convincing at mod to high powers. But that was the only colour I saw.

At low light levels,we see greens first and most easily because the colour receptors in your eyes are most sensitive to light in the middle of the visible light spectrum -- ie yellow-greens.

The 10" ditto but a more saturated lime green.

When I got the 12" I wasn't expecting to see any other colour but was taken by surprise (I expected "other" colours would only kick in at 16" and above) when I started to see faint blues along the "wings" of M42 and very occasional dirty pinks elsewhere but only in a true dark sky.

With 18", the lime green colour is visible while observing even in the Sydney CBD at Sydney Observatory. At a dark site the lime green is overpowering with bluish overtones in the "wings" and dull sorta pinky-russet away from the very brightest portions and areas close by the wings and elsewhere. Easier and easier in 24".

No one has mentioned nearby M43, but on a couple of occasions in excellent condiitions with the 18", the whole of M43 has looked a dull browny-red which I found quite strange as it is has comparitively low surface brightness -- _compared to_ M42.

Only on very good nights with the 18" does Eta Carinae (NGC 3372) have any very faint lime colouration in the very brightest parts.

The Tarantula (NGC 2070) is distinctly bluish from 10" and up at least with the colour intensifying with aperture. M17 also shows a distinct lime green in 10" and up. M8 is also a somewhat fainter lime green in 10" and up.

Colour in these non-stellar objects is tremendously subjective and as others have noted is dependent on the experience level of the observer -- your perceptons of what to look for and what to expect are important. Jupiter is a good example of this. At Sydney Observatory, many people cannot see any colour in Jupiter's cloud bands until I tell them what to look for and where -- then all of a sudden they see it. Same for the greenish tinge to the albedo features on Mars (they only look green because of contrast with the otherwise apricot pink areas). Many novices see them as simple grey until their experience at the eyepiece grows.

Interestingly, I believe David Malin continues to contend that it is not possible at all to see colour in M42. He only sees it as grey and denies colour is detectable in the human eye at that light level. Hmmm ...

The overwhelming majority of amateurs beg to disagree I think. The younger the observer, the easier it is to see colour. I speculate this is because of yellowing of the cornea as we get older from U.V.

_Wear those U.V resistant sunglasses religiously folks_! Mine are almost welded on for that reason -- also cataracts run in my family.

Best,

Les D