Why does the Moon appear gray when passing between the Sun and the Earth?

  • Shouldn't the Moon appear as bright as a full Moon seen at midnight from Earth?



    Moon photobombs Earth



    The photo was taken by DSCOVR at Lagrange point 1.



    In the picture, The Moon appears dark gray. Of course the Earth appears bright, reflecting sunlight from clouds and water. The Moon's surface is gray and should reflect less light than the Earth.



    It should be irrelevant that we see the far side, since the reflectivity of the Moon's surface should be the same on the far side as the side that faces the Earth.



    The midnight full Moon appears much, much brighter as seen from Earth than it does in this picture, despite the fact that the amount of sunlight reflecting from the surface of the Moon is the same in both instances.



    I understand the photo was taken with 3 separate exposures of red, blue and green, but this should not affect the brightness.



    So why does it appear so dull?


    Actually the far side is a bit brighter than the near side. (*Far* and *near* being relative to the Earth.) So it does make a small difference.

    At night you compare the moon to the blackness of space right next to it. So it seems to be white. But the moon's albedo (0.14) is only slightly higher than worn asphalt (0.12), so it is actually dark grey. Compare Earth (albedo 0.30) - much brighter. The picture doesn't seem over- oder underesposed, either - a miniature Earth and Moon wook look just like that in broad daylight (well, in front of a screen of vantablack)

    This answer mentions the moon, issues of albedo, and is somewhat "*what the moon really looks like*" - related.

  • uhoh

    uhoh Correct answer

    6 years ago

    That's what it really would look like if you were there with DSCOVR. The albedo of the Moon is only about 0.136, about half of the Earth's average albedo. Of course the part with clouds is higher.



    I was shocked too, but it was explained in written copy that accompanied the release of the original image.




    Shouldn't the Moon appear as bright as a full Moon seen at midnight from Earth?




    It does. If the moon were a diffuse, white ball, a full moon would be about seven times brighter!



    If you watch the image or GIF, the Moon is roughly the same brightness as central Australia or the Sahara region.



    Phil Plait explains well in Bad Astronomy.



    There's a lot to read here.



    EDIT: I just ran across these images of astronauts on the surface while reading this answer. Their suits are not 100% white to begin with, but the Lunar soil - at least in these locations - is significantly darker. It is close to the same color as the (presumably) nearly-black radiator fins for the heat sink of the RTG unit (2nd photo) at the astronaut's foot.



    enter image description here



    above: "Buzz Aldrin carries the EASEP." from here



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    above: "Astronaut Alan L. Bean from Apollo 12, put the Plutonium 238Pu Fuel from the Lunar Module into the SNAP 27 RTG" from here.



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    above: Image from NASA/NOAA from Bad Astronomy


    To give some perspective, 0.14 is about the albedo of aged asphalt pavement. The moon is actually pretty dark.

    If you live near a planetarium or other museum that has a moon rock on display (I'm lucky enough to have worked at one), and have seen a moon rock up close, you'll note that the moon rock is dark grey with light specks throughout (at least the sample I've seen was). So it's no surprise that the entire moon is quite dark.

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Content dated before 7/24/2021 11:53 AM