shadow. Putting in the longitude/latitude/altitude coordinate values -310.8,10.9,0 into JPL Horizons we see that the predicted time of mid-transit was 04:00:36 UTC, in perfect agreement within the error of determining the exact longitude and latitude of the center of the shadow. This was about 14:41 Martian local solar time, and the Sun's altitude was 46.5° above the horizon. JPL Horizons also shows that on 26 August 1999 the distance between the Earth and Mars was 9.6 light-minutes. Other images Many dozens of other images of the shadow exist, but these are much lower resolution (by a factor of 27/4). Three such images are shown in the 1 November 1999 NASA press release. The timestamps printed on the photos in the NASA press release do not correspond to the actual time that the shadow was imaged, rather they represent the "image start time" of a vertically much larger original image. Mars Global Surveyor orbits Mars in a Sun-synchronous polar orbit with orbital period 117.65 minutes, moving from south pole to north pole, and continuously points its camera straight down. The result is an image in the form of a very long thin vertical strip, where the pixels in the top part of the image are imaged nearly one hour after those in the bottom part of the image. In principle the image could be as much as 43200 pixels high, but "downtrack summing" is used to merge adjacent lines. For instance, a downtrack summing factor of 27 causes every 27 lines to be merged into one, resulting in an image 1600 pixels high. Thus to determine the actual time that the Phobos shadow was imaged, it is necessary to locate the original image and measure how many pixels from the bottom of the image the shadow is found and add the corresponding offset to the image start time. For example, we examine the image labeled with the timestamp 1 September 1999 20:13:05 (UTC). We have the original images M07-00166 (red) and M07-00167 (blue), part of the gallery of MOC Global-Map Images, Subphase M07. The shadow is situated at roughly 14°N 236°W. In this case the image start time is 20:13:04.69 UTC, the line integration time is 80.48 milliseconds, and the downtrack summing factor is 27. The shadow is about 8 pixels high, centered at 993 pixels from the bottom of the original 1600-pixel-high image. We add (993 × 0.08048 × 27)