Light Reflection-Albedo

Albedo is a measure for reflectance or optical brightness of a surface. It is dimensionless and measured on a scale from zero to one.1

No stars, even though the moon has a low albedo especially from standing on its surface. Albedo is the reflective index of a surface. As an example, the albedo of worn asphalt is 0.12 and the reflectivity of snow is 0.80 to 0.90. The albedo of the moon is 0.13. The Earth on the other hand has an albedo of 0.38. So the moon is only fractionally more reflective than worn asphalt: common old road surface material. That means, the reflection of the sunlight off the Moon’s surface would not impinge on the ability of an astronaut, or his camera, from seeing stars in the pitch blackness of outer space. The brightness of the Moon as seen from Earth appears to be high. This is because we are seeing, at full moon, more than half the Moon’s surface area. Divide the number of square meters of Lunar surface by 0.13 and you can see why the astronauts were only seeing a tiny fraction of the reflected light off the Lunar surface.

Not all the light reflected is aimed at an astronaut's body. Reflected light generally goes straight back into outer space. When standing on the Moon, the astronauts would be in outer space. There is no atmosphere to divide the Moon's surface from the emptiness of space. Therefore, the reflected light is not defused, it travels in a straight line towards the Earth or beyond. Even when facing away from the Sun the Apollo photographs show no stars. Sunlight cannot diffused and illuminate space. Nothing can illuminate the blackness of space. The astronauts would have encountered a pitch black ‘Lunar sky’ with millions of stars.

ISS in orbit with and without stars.

No Stars

The image above is from NASA and shows the ISS. The image directly above is a photo enhanced closeup of the same image. You can clearly see stars even though the earth is shining with reflected light much more than the moon does.

So why are there no stars in the first hand image? The answer can only be that it is policy to remove the stars from NASA images taken in low earth orbit. This gives validity to their moon landing photographs.

The above image is from NASA iss052e056225 (Aug. 21, 2017) . When enhanced in PSP 9, it shows stars.

This image from NASA, after enhancement, shows stars. Look carefully and you will find the constelation scorpius!

And above more stars different image.

The total surface area of the Moon is 37.9 million square kilometers, or 14.6 million square miles. Need some context? The surface area of the Earth is 510 million square kilometers. In other words, the total surface area of the Moon is only 7.4% the surface area of the Earth.2

Glare can reduce visibility by:

  • reduction of brightness of the rest of the scene by constriction of the pupils
  • reduction in contrast of the rest of the scene by scattering of the bright light within the eye.
  • reduction in contrast by scattering light in particles in the air, as when the headlights of a car illuminate the fog close to the vehicle, impeding vision at larger distance.
  • reduction in contrast between print and paper by reflection of the light source in the printed matter (veiling glare).
  • reduction in contrast by reflection of bright areas on the surface of a transparent medium as glass, plastic or water; for example when the sky is reflected in a lake, so that the bottom below or objects in the water cannot be seen (veiling glare).
  • bloom surrounding objects in front of glare.

As the Moon has no atmosphere there is no gasses to reflect light into different direction causing side glare. There are no bodies of liquid to cause glare and surrounding objects are minimal (the LEM).

More

Albedo is a measurement of the amount of light reflected from the surface of a celestial object, such as a planet, satellite, comet or asteroid. The albedo is the ratio of the reflected light to the incident light:

$ A= \frac{\text{reflected light}}{\text{incident light}} $

and has values between:

  • 0: a black object that absorbs all light and reflects none; and
  • 1: a white object that reflects all light and absorbs none.

Planets and satellites with clouds tend to have a high albedo, while rocky objects such as asteroids have a low albedo. The albedo of an object changes with wavelength, depending on the efficiency of reflection for different parts of the electromagnetic spectrum. The albedo of the Earth changes slightly with the seasons, due to differences in the amount of cloud cover and the presence of snow in either hemisphere and at the poles.

The table below gives approximate values of albedo for each of the planets, the Moon and Pluto:

Planet Bond Albedo Geometric Albedo
Mercury 0.12 0.14
Venus 0.75 0.84
Earth 0.30 0.37
Moon 0.12 0.11
Mars 0.16 0.15
Jupiter 0.34
Saturn 0.34
Uranus 0.30
Neptune 0.29
Pluto 0.4 0.44-0.61

Bond albedos – total radiation reflected from an object compared to the total incident radiation from the Sun. Geometric albedos – the amount of radiation relative to that from a flat Lambertian surface which is an ideal reflector at all wavelengths.3

1. Wikipedia Article: https://en.wikipedia.org/wiki/Albedo

2. universetoday.com/19925/area-of-the-moon

3. http://astronomy.swin.edu.au/cosmos/A/Albedo

https://upload.wikimedia.org/wikipedia/commons/8/8a/ISS_after_completion_%28as_of_June_2006%29.jpg

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