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Originally Posted by Mossie  Can somebody tell me as a complete novice. Are the colours in those photos as you would actually see the nebula if it were possible to see it with the naked eye or is it just one part of the light spectrum. |
In a word NO
Even if these nebulae where on your doorstep, so to speak, and filled half the sky they would possess little or no colour at all because they are inordinately faint and our eyes are designed to register colour in bright conditions eg daylight.
Proof of this is our own Milky Way galaxy in which we reside - it appears as a faint irregular colourless band of light arching overhead from horizon to horizon in summer and autumn under dark moon-free skies remote from artifical light in areas of low human population. And the Milky Way is typically brighter than many of the nebulae recorded by Hubble ST.
To record nebulae the camera exposures may run to an hour which is ~ x18000 longer than the integration 'exposure' of the eye. Also to highlight various 'glowing' elements in the nebula special filters are used to record in sequence hydrogen [H-alpha], oxygen [OIII] and sulphur [S] and allocate red, green and blue colour to each element. This wouldn't resemble what the eye could see if it were sensitive enough to view colour this faint. There are various artificial 'palettes' - the Hubble 'palette' is used on reconstructed colour images from the Hubble ST - where the results, as mentioned, are fantastic if unreal
