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Originally posted by GaryN
I need some help here. I'm trying to find out what the brightest light levels were for the astronauts on the Lunar surface. I am told the stars could not be seen because the surface was too bright to allow the stars to be seen, but from all the info I have been able to find, the brightest light they worked under was equivalent to the light level 15 minutes after sunset in Texas in July. How bright is that? This document talks about the limitations due to low light levels, but does not mention the times when the surface would have been blindingly bright. Anyone have any further info?
An investigation into the levels of ambient lighting on the lunar surface indicates
that for most nearside locations, illumination will be adequate throughout most of the
lunar night to conduct extravehicular activities (EVAs) with only minor artificial illumination.
The maximum lighting available during the lunar night from Earthshine will be
similar to the light level on a July evening at approximately 8:00 p.m. in the southern
United States (approximately 15 minutes after sunset). Because of the captured rotation
of the Moon about the Earth, the location of the Earth will remain approximately constant
throughout the lunar night, with consequent constant shadow length and angle.
Variations in the level of Earthshine illumination will be solely a function of Earth phase
angle. Experience during the Apollo Program suggests that EVA activities conducted
during the period around the lunar noon may be difficult due to lack of surface definition
caused by elimination of shadows.
From page 11:
The Apollo lunar excursion module (LEM) is presently scheduled for lunar landing in sunshine conditions. However, several operational constraints presently impose severe penalties on the Apollo mission launch window. The extension of the LEM landing capability to include certain earthshine conditions provides additional latitude where these constraint6 are concerned.
The results of this study indicate that lunar earthshine landing operations should not be attempted at or below 0.009 ft-L. The percentage of unsuccessful approaches (fig. 9) and observer comments (table 111) indicate that LEM operations in brightness levels between 0.009 ft-L and 0.04 ft-L could endanger crew safety. Observer coments indicate that a high level of confidence did not occur until a brightness level of 0.06 ft-L was obtained.
The acceptable pilot's confidence level appears directly related to the brightness level at which terrain elevation could first be observed. Terrain texture, visible at 0.04 ft-L,was the final factor to cause a change in rate of selection, commitment, and approach times. There were no unsuccessful approaches at or above the brightness level of 0.0325 ft-L. These factors indicate that 0.06 ft-L is definitely an operationally feasible brightness level. It is also apparent that a lower minimum could exist at 0.04 ft-L. Simulators should be used to train the flight crew in initial lunar approaches.
Using logic, I can imagine it would also be bright for an astronaut walking on the surface.
No athmosphere = bright as soon as the sun light is direct.
Originally posted by GaryN
So why did they practice landing in very low light levels, when they knew exactly the window of time they would be landing in?
The Apollo lunar excursion module (LEM) is presently scheduled for lunar landing in sunshine conditions. However, several operational constraints presently impose severe penalties on the Apollo mission launch window. The extension of the LEM landing capability to include certain earthshine conditions provides additional latitude where these constraints are concerned.