Quote:
On 2002-08-01 10:02, JayUtah wrote:
In addition to various discrepancies about the dates of certain photographs, bear in mind that the translunar trajectory is not a straight line. Both the earth and the moon will go through changes of phase as seen from the spacecraft en route simply due to the spacecraft's change in position. That doesn't hold for circular orbits, but if any of the dates for the photos place the spacecraft en route, you can't make generalizations about phase.
As for the apparent fluctuation of the earth in the sky in the J-missions, recall that the J-missions lasted for three days, producing a difference in sun elevation of up to 30° between photographs. Further, the local horizon is not necessarily a good approximation of the theoretical horizon, especially on the moon where the horizon is actually much closer to the photographer.
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The relevant images from A11 are 44-6550 and 44-6642 which show the earth phases exactly as expected. The first image taken from the command module shows the Earth phase as something more than half. The writer says 2/3 but I estimate it is less than that. The second picture (6550) is taken at the time of rendezvous with the ascent module when the moon has moved a day (or more) further in its easterly orbit around the Earth and it thus appears that the terminator has "moved" westward by what looks to be the 13+ degrees expected.
WRT the A17 images, the height of the sun in the lunar sky would indeed change by the aforementioned 13 degrees per day, but that would only affect the earth's phases, not its position in the lunar sky. The proper explanation to the apparent anomaly is that the true horizon can't be seen, or even deduced, from any of the pictures, just as Jay's post states. I think what's notable is that the change in the position of the terminator over the period the three images were made (one in each of the three EVA's) is exactly as expected. It appears to move westward at about 13 degrees per day. This tells me the pictures are indeed exactly as advertised.