Results of first orbit of Neptune observation:

General Information: Two Hubble Space Telescope orbits were devoted to imaging of Neptune, orbits 2 and 3 (Pluto got orbit 1). In each orbit, six images were taken at wavelengths ranging from blue to red. One of Heidi Hammel's journals gives us insight into why she decided on these filters.

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. The very bright spot at about 11 o'clock on the edge of the planet in image 203 is a cosmic ray, a blemish on the image.

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).