Making a Mosaic - Part II
As MESSENGER approached Mercury on January 14, 2008, the Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS) snapped images of the nearing planet in a sequence that covered the entire sunlit portion of the surface. This mosaic was made from these images, shown as thumbnails on the image context sheet released last week. This mosaic is shown in a cylindrical equidistant (also known as equirectangular) projection, which simply is a map with longitude lines being vertical and equally spaced and latitude lines being horizontal and equally spaced. The mosaic covers the entire approach crescent view of Mercury, so the vertical extent of the mosaic is comparable to Mercury's diameter of 4880 kilometers (about 3030 miles). Surface features on the right side of the mosaic show long shadows that accentuate height differences because these images were taken near Mercury's terminator, the transition between the sunlit dayside of the planet and the dark night side; the previously released image of the crater Matisse is an example of one of these near-terminator images used in the mosaic. Features near the left side of the mosaic are looking toward the limb of the planet, and this very low viewing geometry and higher Sun angle do not provide much detail about the surface structures; the previously released image looking at Mercury's horizon is an example of such a view that was used to create this mosaic.
This low-resolution version of the mosaic is only 8% of the resolution of the full mosaic and contains only one pixel for approximately every 156 pixels in the original images.