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Post by mopc on Jul 18, 2011 16:31:00 GMT -4
I was wondering what was special with the Apollo 17 moon trajectory that enabled it to take the only pictures of the Earth fully lit by the Sun of all Apollo missions.
After all, all Apollo trajectories were pretty much "toward the Sun" give or take a few degrees, since they were launched usually at the limit between a New Moon and a Waxing Moon phase, so the moon was on the way to the Sun, right? So all Apollo landing missions basically could see a fully lit Earth on their way to the Moon, correct?
I would guess the fact that Apollo 17 was launched at nighttime would have something to do with it, since they ended up leaving earth orbit at a different time, so maybe the other Apollo crews were either sleeping or involved in a scheduled activity that prevented them from taking pictures of the Earth so close; when they had time it was too far. Is that it?
Did the other Apollos take pictures of the Earth at all (before orbiting the Moon?)
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Ian Pearse
Mars
Apollo (and space) enthusiast
Posts: 308
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Post by Ian Pearse on Jul 18, 2011 16:51:46 GMT -4
mopc, one of the links at the bottom of this page is to the Apollo Lunar Surface Journal. In there, amongst other things, you will find an awful lot of Apollo photographs. I would suggest you browse for a while and you may find you can answer your own question.
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Post by echnaton on Jul 18, 2011 17:54:36 GMT -4
MOPC,
Some of this may be of help. The landings were all made so that the landing zone was experiencing lunar morning. This was done so as the LM came in from the east, the sun would cast shadows on the uneven lunar terrain to give the surface some detail. and the shadow of the LM itself would give clues about the distance to the ground. At noon, the surface would look flat, local details would be washed out and depth perception very limited. If you look at a full moon through a telescope you will notice the flatness of the image. The launch windows were all keyed to the landing times but missions also spent varying amounts of time in orbit before landing.
No lunar surface photos could have shown the earth fully lit, because that only happens during a new moon when the near side is in darkness. A17 landed furthest to the east of all the missions and IIRC also landed very early in the lunar day. As a result, it launched on the new moon and was able to take the closest to full images of the earth of all the missions. These were taken during the trans lunar coast.
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Post by Kiwi on Jul 19, 2011 10:03:05 GMT -4
The sticky thread near the top of this section, Thumbnails of Apollo lunar surface photos can also speed up a search for photos by giving the number of a specific photo to hunt down at the ALSJ or Kipp Teague's Project Apollo Archive. ...so the moon was on the way to the Sun, right? Depends how you look at it. From our perspective on earth, the moon is closest to the sun at New Moon and therefore the earth is fullest from the moon at that time. When the moon is waxing it's moving away from the sun right through until Full Moon. And an Apollo translunar trajectory early on heads toward a place well in advance of the leading edge of the moon, so for some of its journey is even further from the sun than the moon. Did the other Apollos take pictures of the Earth at all (before orbiting the Moon?) Without searching all translunar photos, yes and no, probably. Armstrong, Aldrin and Collins hardly saw the moon at all until they got close to it, but got good views and photos of the earth. They saw, photographed and videoed the moon on the way back, and Charlie Duke embarrassed himself when he mistook the moon for earth on the big TV screen in Mission Control. With other missions it might have been the other way around. Remember too that they had to set up the barbeque roll to even out the temperature by turning the stack so it lay at right angles to the sun's rays (so I believe but could be wrong), therefore opportunities for viewing earth or the moon may have been limited, depending on the particular orientation of the stack.
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Post by ka9q on Jul 20, 2011 17:59:54 GMT -4
I think, but am not certain, that the axis of the barbecue rolls was more or less perpendicular to the transfer orbit plane. That caused the earth, moon and sun to appear sequentially in each of the CM windows.
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