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  Sun, Earth orientation from lunar surface

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Author Topic:   Sun, Earth orientation from lunar surface

Posts: 678
From: Hudson, MA
Registered: Jul 2005

posted 10-21-2007 08:24 AM     Click Here to See the Profile for Paul78zephyr     Edit/Delete Message   Reply w/Quote
When the Apollo astronauts were actually on the lunar surface how — or perhaps more specifically where — did the Sun and Earth appear in the lunar sky? Was the Earth always visible?


Posts: 2141
From: Essex, UK
Registered: Jul 2001

posted 10-21-2007 09:18 AM     Click Here to See the Profile for nasamad   Click Here to Email nasamad     Edit/Delete Message   Reply w/Quote
The Earth was always visible to the astronauts as the landings were all on the side of the moon that faces Earth. (But may have seemed invisible at some point due to the moon facing side being in darkness, I'm not sure how the tilt may have illuminated the poles).

For all Apollo landing missions the height of the Earth in the sky was different as the landings took place at different lunar latitudes and longitudes.

The sun was always visible as the landings took place not long after lunar sunrise at each landing site. This was to take advantage of the increased shadows and contrast to aid the landing, plus if the sun was directly overhead during the mission the thermal effects on the vehicles and astronauts would have changed.


Posts: 177
From: Utrecht,NL
Registered: Feb 2007

posted 10-21-2007 10:04 AM     Click Here to See the Profile for BA002   Click Here to Email BA002     Edit/Delete Message   Reply w/Quote
Interestingly, at last week's Autographica show, Eugene Cernan pointed out that you can see that the Earth was at a lower altitude above the horizon on Apollo 17 than on Apollo 15 and Apollo 16 by looking at the angle in which the antenna on the rover is pointing.

And indeed, if you watch the Apollo 17 DVD by Spacecraft Films you can see that the camera operator at some point aims the camera more or less by looking at how the antenna of the rover is pointed and then finds the Earth in the sky, not too far above the horizon. The CapCom then tells the astronauts that Houston has a wonderful view of Earth and Cernan proceeds to look up as well, an incredible moment!


Posts: 1647
From: Smithfield, Me, USA
Registered: Mar 2005

posted 10-21-2007 10:41 AM     Click Here to See the Profile for MCroft04   Click Here to Email MCroft04     Edit/Delete Message   Reply w/Quote
I find myself on the road without access to my Apollo 17 DVD, but I thought that because all the lunar missions landed near the lunar equator that the Sun was always high in the sky? Granted the further away from the equator (as in Apollo 17) then the lower the Earth would appear. However, I don't recall any missions where the Earth was "not too far above the horizon."

In fact, when I attended the American Association of Petroleum Geologists (AAPG) field trip to Johnson Space Center hosted by Jack Schmitt in 2006, he made a point at the lunar diorama (at Space Center Houston) that it was very realistic except that the Earth was too low on the horizon (an exception was made on the diorama because they did not have enough room to place the Earth at the proper location high in the sky).

Perhaps in your example above the Earth was observed over high mountains, making it appear near the horizon? I'll check the DVD when I get home.


Posts: 26
From: Karlsruhe, Germany
Registered: Apr 2005

posted 10-21-2007 03:23 PM     Click Here to See the Profile for FordPrefect     Edit/Delete Message   Reply w/Quote
From all the Apollo missions landing on the moon, Apollo 17 had the Earth at the lowest altitude above the horizon perpendicular to the local vertical at the landing site.

Not only the latitude is a factor but the longitude of the landing site as well, since the near side of the Moon always more or less (libration) faces the Earth.

The Taurus-Littrow valley is not only located 20 degrees north of the lunar equator but also 30 degrees east of the null meridian (that is to the right of the center vertical 0 degrees longitude when you look at the Moon from Earth), therefore the Earth was approximately only 42 degrees above the local horizon. Also, due to the longitude of this landing site (and the given sun angles at landing time constraints) the crew of Apollo 17 saw the Earth at the highest disk illumination during the lunar surface stay of all missions.

One photo showing Gene and the Earth above is this one.

During EVA 2 at Station 2 at Nansen crater, they took a photo "upslope" the South Massif with the Earth in the image as well. This photo looks like the Earth would be low over the horizon but of course this is only due to the 30 degree slope of the massif at the foot they are standing of. The respective photo is this here.

With all the remaining Apollo landing missions, the Earth was much "higher" above the landing site's local horizon, more or less vertically and the disk illumination was much less at the time of landing (disk illumination of course decreased with time progressing for all landing sites).


Posts: 1758
From: Killingly, CT
Registered: Mar 2002

posted 10-21-2007 04:19 PM     Click Here to See the Profile for ejectr   Click Here to Email ejectr     Edit/Delete Message   Reply w/Quote
Looking at the semi circle lighted portion of the Earth and its angularity in these photos, you can just about tell that this photo was taken on a day that wasn't that far from the winter solstice in December.


Posts: 177
From: Utrecht,NL
Registered: Feb 2007

posted 10-22-2007 12:26 PM     Click Here to See the Profile for BA002   Click Here to Email BA002     Edit/Delete Message   Reply w/Quote
I guess my qualification of the angle as "not too high above the horizon" should be read in a sense that I don't recall many or even any other instances where the rover camera shows the Earth above a visible lunar surface, but as I read through the ALSJ at 143:20:14, that was indeed caused by the upslope of the Massif at about 25 degrees, which shows the Earth at apparently just 20 degrees above the "surface."


Posts: 297
From: N.Ireland.
Registered: Jul 2002

posted 10-27-2007 02:57 AM     Click Here to See the Profile for derek   Click Here to Email derek     Edit/Delete Message   Reply w/Quote
I note that the Apollo 12, 15 and 16 crews never seem to have photographed the Earth during EVA, all I can find are those taken on 11, 14 and 17.

All times are CT (US)

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