by apodman » Sat Jul 26, 2008 2:08 pm
MadcityTraveler wrote:I would enjoy seeing some of the images ... of the subject in visible light.
This may be a useful suggestion in general.
If you are referring to
Central IC 1805 (APOD 2008 July 26) ...
APOD wrote:A composite of narrow and broad band telescopic images, the view ... includes emission from hydrogen in green, sulfur in red, and oxygen in blue hues.
I think they are saying this composite is made of several photos, all in visible light. I think the "broad band" image includes most if not all of the spectrum of visible wavelengths, and that the listed elements' appearance is accentuated by adding photos taken with filters that only pass the desired emission wavelengths, also in the visible range. Or there could be non-visible wavelengths shown as color - the text doesn't say specifically.
Here's a false-color view of IC 1805:
http://antwrp.gsfc.nasa.gov/apod/ap040917.html
Here's a
futher explanation of a common color mapping scheme:
"The final image depicts
red light from hydrogen atoms
as green,
red light from sulfur ions (sulfur atoms with one electron removed)
as red, and
green light from doubly-ionized oxygen (oxygen atoms with two electrons missing)
as blue."
So I guess that makes the color in this picture visible but false.
[quote="MadcityTraveler"]I would enjoy seeing some of the images ... of the subject in visible light.[/quote]
This may be a useful suggestion in general.
If you are referring to [url=http://antwrp.gsfc.nasa.gov/apod/ap080726.html]Central IC 1805 (APOD 2008 July 26)[/url] ...
[quote="APOD"]A composite of narrow and broad band telescopic images, the view ... includes emission from hydrogen in green, sulfur in red, and oxygen in blue hues.[/quote]
I think they are saying this composite is made of several photos, all in visible light. I think the "broad band" image includes most if not all of the spectrum of visible wavelengths, and that the listed elements' appearance is accentuated by adding photos taken with filters that only pass the desired emission wavelengths, also in the visible range. Or there could be non-visible wavelengths shown as color - the text doesn't say specifically.
Here's a false-color view of IC 1805:
http://antwrp.gsfc.nasa.gov/apod/ap040917.html
Here's a [url=http://hubblesite.org/gallery/behind_the_pictures/meaning_of_color/eagle.php]futher explanation of a common color mapping scheme[/url]:
"The final image depicts [b]red[/b] light from hydrogen atoms [b]as green[/b], [b]red[/b] light from sulfur ions (sulfur atoms with one electron removed) [b]as red[/b], and [b]green[/b] light from doubly-ionized oxygen (oxygen atoms with two electrons missing) [b]as blue[/b]."
So I guess that makes the color in this picture visible but false.