Quote:
Originally Posted by Don Pensack
Actually, nebulae emit more energy in H-alpha wavelengths, but out eyes are insensitive to light that deep in the red, so having an h-alpha transmission in a filter doesn't help us see them at all.
|
Hi Don,
You read this comment repeatedly on astronomy forums but unfortunately it's incorrect. The human eye will generally have a sensitivity range from 400nm to 700nm which includes the H-Alpha line at 656.3 nm. Some individuals have a sensitivity up to 730nm to 750nm. Whilst red lasers usually emit at 632nm (the cheap ones emit up to 650nm), visible red light has a wavelength of around 650nm, which is just under the H-alpha line.
Here is a link to some commentary on this on the NASA website.
http://science-edu.larc.nasa.gov/EDD...or_Colors.html
Of course this varies from individual to individual and there is a large percentage of the population that will in fact not be able to see as deep into the red as others. I have seen this situation manifest repeatedly on the observing field. Andrew Murrell and I can both see quite deep into the red. There have been quite a few targets that we have been able to see reasonably easily because of our deep red sensitivity yet other skilled observers have been unable to see these targets, or parts of them, because of their insensitivity at the high red end of the spectrum.
Cheers,
John B