A map of Neptune
This map of Neptune was created from 9 sets images taken by the Voyager 2 spacecraft in August 1989 from a distance of approximately 10 million km. Each set consisted of images taken through orange, green and blue filters. These were used as red, green and blue, respectively. This means that a total of 27 images was used.
The first step was to calibrate the images. This resulted in radiometrically corrected images that had various artifacts removed (e.g. uneven camera sensitivity across the image field, blemishes etc.). I then processed the images in Photoshop to remove noise and other defects that were not removed during the previous processing step. The images were then reprojected to simple cylindrical projection, compensating for the different illumination across different parts of the planet on the fly. To do this I first determined three different sets of photometric parameters, one for the orange images, one for the green ones and one for blue. To reproject the images I also had to reverse engineer the viewing and lighting geometry of the images since when making the map I had absolutely no information on this. I then composited the resulting maps into 9 colored maps (one for each of the 9 sets of images). I then mosaicked these into one big map and removed the seams between the maps. To do this I had to modify two of the maps, the 'first' and 'last' ones. The reason is that due to Neptune's powerful east-west winds, different features take different times to complete a 360° rotation, in some cases resulting in longitudinal changes of tens of degrees over one Neptunian day.
The final step was to add some fictional data. This was necessary since Voyager 2 had Neptune's southern hemisphere in view, thus no data is available for regions northward of roughly 50°N. I added this data by cloning regions in the southern hemisphere and then making some changes to avoid making the north polar region look exactly like the south polar region.
Click the map below to download the full size map (309 KB 1800x900 pixel JPG).
The map is in simple cylindrical projection with latitudes running with a uniform interval from -90 (bottom) to 90 (top) and longitude 0 at the left edge of the map (although longitudes are of little importance for planets like Neptune which has no fixed features, just clouds). Latitudes are planetographic. The map should be rendered by projecting it onto an ellipsoid with an equatorial radius of 24764 km and a polar radius of 24343 km or some equivalent units. See also my planetery rendering tips page for further info.
This map should be considerably more accurate than previously available maps, the resolution is higher and there are no 'handpainted' features except for the cloned areas in the north. However, it should be noted that Neptune's appearance changes greatly over time. For example, the Great Dark Spot that was present in Neptune's southern hemisphere during the several months that Voyager 2 observed the planet has now disappeared. Instead, big dark spots have been spotted in the northern hemisphere. I made no attempts to show this in the map, it is intended to show Neptune's appearance back in 1989.
Also the color is probably more realistic than in most other maps by being somewhat less saturated. Despite this I feel it should be even less saturated than here, i.e. the overall color should probably be more whitish.
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