by geckzilla » Sun Dec 17, 2017 2:25 am
I was studying the latest Neptune imagery from Hubble, which is already free to the public due to being part of the Director's Discretionary programs, when I was surprised to see limb brightening in the red end of the visible spectrum. I am aware that the methane bands in near-infrared exhibit this phenomenon, but had no idea that it could possibly be human-eye-visible.
The reason for this being that no other Neptune image claiming to be "natural" (I dislike this word in this context) showed anything other than a blue to cyan sphere with whiteish clouds. Some of them showed reddish or greenish limbs, but I figured those either used infrared or were maybe just bad processing.
After seeing this in the Hubble archive, I decided to get into the Voyager archive, which I really thought had been gone over by now with many fine toothed combs. My understanding is that Voyager 2's visible filters went like this: violet, blue, green, orange. Most of the processors use the "orange" filter in place of red, so I had assumed Voyager 2 couldn't see much red.
I noticed the "green" filter exhibited a certain kind of limb brightening that reminded me of the Hubble dataset. Why did this "green" filter fit the pattern of a red one? I decided to check the
filter plot and there it was. That green filter was something I would rather use for red. Furthermore, the violet and blue filters were ones I'd rather use for blue and green, respectively. Heck, there is visible RGB data in the Voyager 2 archive for Neptune.
Lo and behold, when I put the filters together like that, there was that lovely pink limb, most prominent at the north pole. Anyway, just happy to have found this, and thought I would share. I had no idea Neptune was so colorful.
I was studying the latest Neptune imagery from Hubble, which is already free to the public due to being part of the Director's Discretionary programs, when I was surprised to see limb brightening in the red end of the visible spectrum. I am aware that the methane bands in near-infrared exhibit this phenomenon, but had no idea that it could possibly be human-eye-visible.
The reason for this being that no other Neptune image claiming to be "natural" (I dislike this word in this context) showed anything other than a blue to cyan sphere with whiteish clouds. Some of them showed reddish or greenish limbs, but I figured those either used infrared or were maybe just bad processing.
After seeing this in the Hubble archive, I decided to get into the Voyager archive, which I really thought had been gone over by now with many fine toothed combs. My understanding is that Voyager 2's visible filters went like this: violet, blue, green, orange. Most of the processors use the "orange" filter in place of red, so I had assumed Voyager 2 couldn't see much red.
I noticed the "green" filter exhibited a certain kind of limb brightening that reminded me of the Hubble dataset. Why did this "green" filter fit the pattern of a red one? I decided to check the [url=https://pds-rings.seti.org/voyager/iss/inst_cal/vg1_na_green5.html]filter plot[/url] and there it was. That green filter was something I would rather use for red. Furthermore, the violet and blue filters were ones I'd rather use for blue and green, respectively. Heck, there is visible RGB data in the Voyager 2 archive for Neptune.
Lo and behold, when I put the filters together like that, there was that lovely pink limb, most prominent at the north pole. Anyway, just happy to have found this, and thought I would share. I had no idea Neptune was so colorful.
[attachment=0]Neptune1989-08-17T0530.png[/attachment]