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The title basically says it all, but i will elaborate. Earth's moon light up the night sky by reflecting sunlight. But our moon is barren and made up of grey/white rock thus making it highly reflective.

If a planet were to have a moon with an atmosphere and a temperature suitable enough to evolve plantlife and thus take on a green hue, would it still reflect enough light to be a light source in the night sky comparable to our moon or would this ''lush moon'' be so dim as to be ineffective as a nightly lightsource?

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    $\begingroup$ Our Moon is made of very dark rock. The albedo of the Moon is 0.12, about the same as that of the asphalt of the roads. By contrast, a forest of broad-leaf trees has an albedo of 0.15 to 0.18 -- that is, if the Moon was covered in a forest of oak trees it would be 25% to 50% more luminous than it is. Green grassland has an albedo of 0.25, and would make the Moon twice as luminous. Only a very dark conifer forest would lower the albedo of the Moon, and definitely not by more than 25%. $\endgroup$
    – AlexP
    Commented Aug 1, 2021 at 20:51
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    $\begingroup$ The Earth at daytime can be seen from outer space. Even the green, forrest covered parts. Though these are indeed dark. So a moon covered with forest only will be visible but not as shiny white. You could not go for a walk in the moonshine anymore. On top of that, the Earth's atmosphere scatters only blue light so you will not see the dark blue nightsky we see today. $\endgroup$ Commented Aug 3, 2021 at 12:20
  • $\begingroup$ The comment just above is important as it takes into account hue $\endgroup$
    – Alchimista
    Commented Aug 3, 2021 at 14:09
  • $\begingroup$ @AlexP This should be an anwser $\endgroup$ Commented Aug 3, 2021 at 14:29

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Your question contains a very false assumption:

But our moon is barren and made up of grey/white rock thus making it highly reflective.

This is the Moon: Albedo (the part of visible light it reflects) is 0.12 Apollo 11 photo of astronaut on moon surface

Here is another object, that also has an Albedo of 0.12: worn asphalt road A cracked old asphalt road

Very, very, very few people would describe an old asphalt road as "highly reflective"

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    $\begingroup$ The comparison I generally hear is to a new asphalt road, which is even darker. $\endgroup$ Commented Aug 2, 2021 at 13:41
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    $\begingroup$ Worth adding that earths plant life is between 0.05 and 0.25 in albedo. The darkest being forests, the brightest beeing crops with grasslands in between. $\endgroup$ Commented Aug 2, 2021 at 15:40
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    $\begingroup$ @DarrelHoffman You've been listening to the wrong people, then. new asphalt's albedo is between 0.04 and 0.07, depending on how cheap the roadbuilder is, and the size and composition of the aggregate used. $\endgroup$
    – PcMan
    Commented Aug 2, 2021 at 15:44
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    $\begingroup$ Alright - for the record, that was from Neil DeGrasse Tyson. I could probably find it again if you want, but I'm working right now, so it'll be a bit. $\endgroup$ Commented Aug 2, 2021 at 18:29
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    $\begingroup$ Okay, so it actually wasn't Tyson but his guest, Raquel Nuno, that said newly paved road: See this video around 50:20. Neil compared it to the sidewalls of car tires in this video around 4:00. $\endgroup$ Commented Aug 3, 2021 at 15:28
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Under the right conditions, shadows can be cast under the light reflected by Venus.

And this is what a body covered by water and plants look like from space.

enter image description here

Consider that it will be way closer than Venus is to Earth, and stay assured that it will be enough of a light source at night.

You can also see it by yourself: go out and look at the new Moon, if you look carefully you will see that the dark part can actually be seen. It's called Earthshine and it's caused by the Moon reflecting back the sun light cast on it by the lit side of Earth. (image source)

enter image description here

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    $\begingroup$ So my idea of an earth like planet with a ''lush moon'' is theorethically possible without bad side effects for the planet it orbits? $\endgroup$
    – Blue Devil
    Commented Aug 1, 2021 at 16:54
  • $\begingroup$ @Blue Devil Do you know how large a world would have to be to have a dense enough atmosphere and liquid water? Presumably significantly larger than the Moon actually is. Forming or acquiring a moon much larger than Luna might be traumatic for a habitable planet. But if it happened early enough in the planet's history both worlds could recover and develop life by the time of the story. I also note that a more massive moon might slow down the rotation of the planet due to ttdal interactions more and thus move farther from the planet than Luna is from Earth. $\endgroup$ Commented Aug 1, 2021 at 18:18
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    $\begingroup$ @Blue Devil The Moon has a very dark surface, one of the darkest and least reflective objects in the Solar system. Almost any imaginable change to the Moon's surface would increase its albedo, the percentage of incoming light it reflects, and thus make it appear brighter as seen from Earth. $\endgroup$ Commented Aug 1, 2021 at 18:22
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    $\begingroup$ solarsystem.nasa.gov/system/downloadable_items/… This photo clearly shows how much brighter the Earth is than the Moon $\endgroup$
    – Robyn
    Commented Aug 2, 2021 at 6:58
  • $\begingroup$ @BlueDevil I hope the first person in space loses their mind(not literally), centuries+ of staring at the beauty of the moon, only to find the earth looks the same from the opposite perspective $\endgroup$
    – TCooper
    Commented Aug 3, 2021 at 19:55
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Planetary albedo is the percentage of light/radiation reflected back into space by a stellar object.

Using accumulated satellite data going back to the 70's, the Earth's average albedo is around 0.30, or about 30% of the light/radiation Earth receives is reflected back into space.

If the Earth were an ice covered world, the estimated albedo would instead be around 0.80, or 80%. If the Earth were a jungle world, covered in greenery, then the estimated albedo would be around 0.14... rather dim.

Generally speaking, a stellar object with clouds will have a higher albedo, while a rocky object will have a lower albedo.

By way of comparison, Saturn, Jupiter, and Uranus all compare to Earth with scores ranging from 0.30 to 0.34. Venus wins with a brilliant average of 0.75, and the moon trails well behind at around 0.12.

Thus a jungle moon would be rather dim, but only compared to other objects. The average albedo of a jungle world is actually brighter than our current moon. Unless it also managed to have lots of clouds, in which case it would probably match Earth. Distance would also be a factor. After all, the moon is usually quite bright as seen from Earth, due to local conditions.


As a side comment, do keep in mind the strength of mass/gravity and electromagnetic fields needed to keep an atmosphere safe from the solar wind. Unless you are dipping into super-science or fantasy, you might wind up with a dual planet rather than a planet/moon setup.

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    $\begingroup$ I feel like my story dips just enough into the sci-fi/fantasy realm to justify that. $\endgroup$
    – Blue Devil
    Commented Aug 1, 2021 at 20:40
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    $\begingroup$ Although you say a jungle moon would be "rather dim", I note that by your own figures it would be slightly brighter than Earth's moon, assuming it was the same size as seen from the planet. I also note that another word for jungle is rainforest, so perhaps one would expect it to have quite a lot of clouds. $\endgroup$
    – N. Virgo
    Commented Aug 2, 2021 at 3:03
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    $\begingroup$ @Nathaniel Indeed so. I have updated slightly, thank you. $\endgroup$
    – nijineko
    Commented Aug 2, 2021 at 4:10
  • $\begingroup$ Ice reflecting radiation (heat) is one of the feedback loops in current world climate change.. more heat will be absorbed during polar summer, when the ice is gone, acellerating the process.. scied.ucar.edu/learning-zone/climate-change-impacts/… $\endgroup$
    – Goodies
    Commented Aug 2, 2021 at 22:37
  • $\begingroup$ Hard to imagine where the forests would get their water from if there were never any clouds... $\endgroup$ Commented Aug 2, 2021 at 22:37

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