by Ann » Wed Mar 25, 2015 6:23 pm
The way I understand it, the nova was yellow when it was discovered. It seems to me that the only possible reasons for it being yellow are either that Nova Sagittarii has already cooled, or that there is a lot of dust between us and the nova.
Bob King wrote:
As novae evolve, they’ll often turn from white or yellow to red. Emission of deep red light from hydrogen atoms – called hydrogen alpha – gives them their warm, red color.
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. When we see nebulas in the sky, such as the Orion Nebula, they never look red to us. That is because we detect other, shorter wavelengths - primarily OIII and Hβ - when we look at nebulas, and therefore they may look slightly greenish to our eyes. But never red. I can't believe that Nova Sagittarii will ever look yellowish to human eyes because of the contribution of red Ha light to the color of the nova.
Ann
The way I understand it, the nova was yellow when it was discovered. It seems to me that the only possible reasons for it being yellow are either that Nova Sagittarii has already cooled, or that there is a lot of dust between us and the nova.
[quote][url=http://www.universetoday.com/119511/nova-in-sagittarius-brighter-than-ever-catch-it-with-the-naked-eye/]Bob King[/url] wrote:
As novae evolve, they’ll often turn from white or yellow to red. Emission of deep red light from hydrogen atoms – called hydrogen alpha – gives them their warm, red color. [/quote]
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. When we see nebulas in the sky, such as the Orion Nebula, they never look red to us. That is because we detect other, shorter wavelengths - primarily OIII and Hβ - when we look at nebulas, and therefore they may look slightly greenish to our eyes. But never red. I can't believe that Nova Sagittarii will ever look yellowish to human eyes because of the contribution of red Ha light to the color of the nova.
Ann