The first images in the orbit, are the bluest, with a wavelength of 4100 Angstroms. The exposure times were 100 seconds. Very little structure can be seen on Neptune. There may be a hint of the dark band in the southern hemisphere. |
Also fairly blue, with a wavelength of 4670 Angstroms. Neptune is brighter here, so the exposure times are only 40 seconds. The dark band is more obvious. |
Images 203 and 303 are green, 5470 Angstroms. The exposure times for this image is only 14 seconds. Again, the dark band in the southern hemisphere is obvious. |
Images 204 and 304 were taken at red wavelengths, at 6190 Angstroms. These are called "methane-band" images, because at those redder wavelengths, the molecule methane in Neptune's atmosphere tends to preferentially absorb light. The planet thus looks pretty dark, and we had to take long exposures: each was 400 seconds. Notice how different the planet looks in a methane-band image when compared with a green-wavelength or blue-wavelength image. |
The last two images in each orbit, were taken in the far red, at 8890 Angstroms. These are also methane-band images, with even more methane absorption, and hence even stronger contrast between bright clouds and dark planet. |
There are always two 8890-Angstrom images taken in the orbit because cosmic rays are a problem - with two images, you can compare them and see if a bright spot is really a Neptune cloud (it will appear in both) or is instead a cosmic ray (it will appear in only one of the two). |