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I have just read a post in one forum and a guy said that “we can not see any colour even with a giant scope”. But I doubt if it is true or not. Some veteran observers say that it is possible to see nebula colour through huge scopes, even small scopes. One guy claimed that the M42 that he saw was greenish.

But I feel confused at this moment. As a student who studying Biology, I have a concept that we can’t see things with colour.

Is there anyone kind enough to tell me the truth?

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Scotopic vision is color-blind, so the faintest objects will all be seen in B&W. However, if the object is bright enough, and/or the scope is big enough, mesopic vision is activated (in which the cones are partially activated). Under these conditions, you can defintiely see color.
I've seen (and see on a regular basis):
M42: green near Trapezium, rose and peach hues in the fainter parts, reddish hues in the "arches" and a bluish tint to M43 and nearby NGC1977. In a 28" or larger scope, brilliant reds appear.

M8: rose hues
M20: rose hues in brighter parts
M17: rosy hue in "Swan" portion
M57: (big scopes) faint pinkish hue.
and blue or green tints in lots of planetary nebulae.

So yes, colors are visible, but where/when will depend on:
--size of scope (bigger scopes definitely see more color)
--light sensitivity of eyes (the genetic component)
--darkness of sky
--nature of filter transmission (if filter is used)
--experience at the eyepiece (dedicated double star observers learn to see quite subtle hues, for example)

I did an interesting test on M42 recently, using a filter slide and color filters. It was quite interesting to see which parts of the nebula were dimmed and by how much with each filter. I would defintely recommend a UHC-type filter that has a strong broadcast in the H-Alpha end of the spectrum. The nebula definitely has a strong H-Alpha component to its brightness.

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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie


Edited by Starman1 (11/24/07 10:24 AM)

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