Chris Peterson wrote:
Ann wrote:It is easy to photograph Ha emission so that it looks red, but to the best of my knowledge it isn't possible for humans to actually see the red color of Ha emission with their own eyes. The human eye is quite insensitive to the wavelength of Ha, about 656 nm.
Humans can readily see 656 nm light. I have a reference tube that produces this wavelength, and I can look through narrowband filters at the Sun and easily see it. Indeed, everybody who uses an Ha telescope to look at prominences is seeing this color directly. There are even credible reports of a few observers directly seeing red in bright Ha emission nebulas viewed telescopically.
I'm not saying we can't see 656 nm light. I'm saying our eyes aren't very sensitive to it. Certainly, when you look at something that contains Ha light through an Ha narrowband filter you will see this wavelength as long as you see anything at all, because other wavelengths that you would have seen so much more easily are blocked by the filter.
What I'm wondering about is the fact that the nova looks yellow so soon after its discovery. Surely the yellowness of the nova itself can have nothing to do with the Ha light of the nebula around it?
Are there any known examples of yellow-looking but intrinsically blue light sources that look yellow not because of dust, and not because their blue light has been scattered in a reflection nebula around them, but because of the bright red Ha light surrounding them?