What colour is Ha?

[Merlin66 (Ken)]

A very interesting thread.
Having built both a Ha solar scope and various spectroscopes, the concept of colour is VERY subjective.
One of the real issues is the response of the "collector" ie the CCD chip, then the response of the "receiver" ie the display and finally the perception of the naked eye.
Ha as seen visually, ie using a narrow band filter is most definately a deep crimson colour.
There is an "expectation" that Solar images should, for aesthetic reasons show as a deep yellow-orange/ golden colour.....
A red laser beam is red.
A green laser beam is green.
and the sky is sometimes blue.

[Peter Ward]

Originally Posted by gregbradley

Even so the red Photoshop assigns then is not as deep as what you see
through the filter.

Correct.

It is important to understand monitors (regardless of software) are physically incapable of displaying a wavelength longer than the emission of their red pixels, and can only use a narrow sub-set of all the colours visible to the human eye.

Depending on the monitor, all deep reds eg, H-Alpha 652nm and 672 (SII) can only be represented by the lower limit of the hardware, typically 620nm...which is significantly more "orange" than the reality.

[avandonk]

If any one thinks that ANY monitor or print can represent reality just go outside and have a long look!

bert

[Prickly]

As Bert points out there is a real problem here if you are red green colour blind!

cheers
David

[Prickly]

On the issue of rods and cones the sensitivities of each differs with respect to different wavelengths of light. Fortunately rods arent very red sensitive (nor blue either really) which means red lights are good for not wrecking night vision. I'm told that bomber aircraft in one of the world wars used to use blue lights for a similar reason - but the red should be better for preserving night vision from the spectrum of the rods.

http://en.wikipedia.org/wiki/Purkinje_effect

cones spectral response
http://en.wikipedia.org/wiki/Cone_cell

Rods spectral response
http://en.wikipedia.org/wiki/Scotopic_vision

Cheers,
David

[Peter Ward]

I suppose there is one other thing worth mentioning, the actual colour of H-alpha is not subjective.

It has a specific frequency, just as for example, some sounds have a specific frequency: eg Middle C at 261 Hz.

In the case of H-alpha, 652nm equates to a frequency of about 458Thz.

While some individuals may be tone deaf or colour blind, this has little to do with the pitch of a note or colour of a light wave.

[Prickly]

Too true Peter. In the dark our rods just wouldnt pick it up as has been said. I guess if there was enough Ha for our cones (assuming not colour blind) to pick it up it would be the colour of 652nm.

I could see the funny side of it though seeing that the post was what colour is Ha. Bert had a good point.

Also the Purkinje effect is interesting to understand.

Cheers
David