Albedo, Color and the Interesting Case of Lunar Sample 12047,6
One thing that I have learned here at Moon Zoo as a full member-newbie is that when considering the lunar landscape what is dark may not be black and what is light may not be white. A case in point is this photograph that stumped me shortly upon arrival at Moon Zoo.
Luckily, Forum moderator Thomas J introduced me to a term called albedo. He said:
“There are a number of reasons for this change in shade. The reflectivity of the surface material is known as its albedo; material that is highly reflective will have a higher albedo than that which is not as reflective. In some situations certain areas may display high albedo material due to geological activity such as impact effects, volcanic effects and even Moon quakes. It is, therefore, not uncommon to see two contrasting shades in adjacent regions. Also, the Moon’s surface is not flat, the topography rises and falls with slopes, hills and mountains. When the Sun is low in the sky a slight slope downward can leave an area in shade. So, in this image it may be that the material on the right has a higher albedo, or it may be a downward slope on the ground level to the left with a rise to that on the right.”
Why do the tracks of the astronauts on the lunar surface appear darker than the surrounding area? One answer from spacefellowship.com is:
” This effect is most likely due to compaction of a very loose surface powder by simply walking around. The more walking in a given area, the more compaction that takes place, and thus the lower the albedo.”
We know certain areas of the lunar surface have coloration due to crater impacts and lava flows such as the famous orange soil of Apollo 17 near Shorty Crater but generally the lunar landscape was described by the Apollo astronauts as concrete, mouse grey and/or light brown in color.
This brings me to the Apollo 12 lunar sample 12047,6 that is now on loan from NASA to the Seattle Museum of Flight.
Apollo 12 astronauts Pete Conrad and Alan Bean collected this specimen while at the mare region called Ocean of Storms. It is an Ilmenite Basalt sample. From the black and white photograph you can tell that it is a concrete like color not unlike many of the photographs we view here at Moon Zoo. What is interesting is that there is more to this specimen than what you see here and read about in the paper linked to above and that is the albedo effect and color change.
I happen to be lucky and live about 15 miles from the Seattle Museum of Flight. However, it was not until I viewed an online photograph of NASA 12047,6 taken by an amateur photographer visiting the museum that I found out that the sample was on display there. On my first visit I was perplexed as the sample did not look quite like the beautiful one in the photograph but more like the concrete colored black and white photograph, though not quite as drab looking. For a month or so this mystery nagged on me and I went so far as to question the on site guides about the authenticity of the display item. Maybe it was another sample or a copy. However, I was told that it is a genuine lunar sample.
Searching the internet I found reference to color change on the lunar surface:
“The orbiting Apollo astronauts noticed a peculiar phenomenon when they observed the lunar surface at a small angle related to the sun’s light. At such small angle, the lunar surface appeared warm brown colored.”
Yes, the light bulb went on in my head and I returned to the museum several months later. When moving as close to the display case as possible and viewing the lunar rock at a sharp angle, the brown color showed up. So, here is a photograph of NASA 12047,6 taken at the Seattle Museum of Flight by amateur photographer Svacher. Just as the astronauts did, we can see the brown color of the lunar surface when the sun or in this case the viewer is correctly positioned.
Here’s some more related reading:
And thanks to Moon Zoo Team member Katie Joy for providing the following additional information and links:
Lunar Sample Atlas
Katie says: “Thin or polished samples of lunar rock can be quite pretty. Some have hints of orange (glass), others bright green (the mineral olivine), some pink (the mineral spinel.) When you view them under the microscope using polarized light rather than direct light then all the minerals appear as a really bright range of colours and look like a stain glass window.”
A Final Thought:
Being one of many amateur scientists here at MZ, the notion of albedo and color change as it applies to larger natural occurring and unaltered geology samples comes to mind such as the Apollo 12 lunar sample above. Here the surface of the sample is in its natural state showing the color change in the visible light spectrum similar to what the Apollo astronauts would have seen in similar lighting conditions.
Analyzing existing samples at the Johnson Space Center in their natural-unaltered state (if not already performed) while replicating the effect of a lunar sun at all possible angles may provide valuable information about the lunar landscape – a more holistic perspective. It may also give clues to color change of lunar formations helping to explain some anomalies associated with transient lunar phenomena.
Mapping color change of the lunar landscape at specific areas may be a helpful tool to acclimate astronauts as they once again walk on the Moon.
Tom128 is a Moon Zoo participant and a regular contributor to the Forum.