1
$\begingroup$
  1. What would happen if we painted the whole moon with black, will it still reflect light, or it will become invisible?

  2. What would happen if we painted the whole moon with silver paint or make its surface shiny?

$\endgroup$
  • 2
    $\begingroup$ Someone has raised a flag to close the question as "too broad", but I think we should take into account that the OP is "just a curious high school student" (useful information that has been edited out of the original question), the reflectivity of the Moon's surface is an interesting one in its own right, and the two answers (both useful and informative) show that it's not too broad to answer. I'm voting to leave it open: this question adds to our site's library of knowledge. :-) $\endgroup$ – Chappo Dec 31 '18 at 22:38
  • 2
    $\begingroup$ Who the questioner is is not useful information. The question is judged on its own merits. If the question is too broad it is too broad, it doesn't matter if the OP is young, old, tall, short, good at tennis or not. $\endgroup$ – James K Jan 1 at 1:37
  • $\begingroup$ @JamesK strongly disagree with your c̶a̶t̶c̶h̶y̶-̶s̶o̶u̶n̶d̶i̶n̶g̶ ̶q̶u̶i̶p̶ comment. One of the way we make New Contributors feel welcome is by accommodating their first few questions as best we can. Answering this question, or leaving helpful suggestions in comments are fine. But closing a first question because it's not up to snuff per a few close-happy users' standards can needlessly turn off some new users from SE or from asking about the world in general. So it shouldn't be taken lightly, or used as an opportunity to make clever-sounding remarks. $\endgroup$ – uhoh Jan 5 at 8:51
  • $\begingroup$ For what its worth, I don't vote to close. This is an answererable and on topic question. It's not too broad. But if it were too broad or off topic then it should be closed. The criteria are here for a reason. If you visit yahoo answers you will understand why it is we close some questions. Closing is not a "super-downvote" There is a misconception that "bad" questions should be closed. That is not the case. Bad questions should be downvoted. Good questions that are not suitable for the site should be closed. Finally remember that the answer is not for the OP, it is for all readers. $\endgroup$ – James K Jan 5 at 19:03
  • $\begingroup$ @JamesK an SE answer is certainly for the OP, and it's also for other readers. I don't know how the idea started that "the goals and purposes of SE" has to be a singular one-liner. It's important that the OP receives an answer that they find helpful, it's why they have final and absolute say on acceptance. It's also important that new users have a positive experience because a) they are human beings, and b) they will come back, ask more questions, and SE sites will continue to grow and produce a nice, realistic, healthy mix of mostly good and a few not-so-good posts. $\endgroup$ – uhoh Jan 6 at 1:43
7
$\begingroup$

The moon is already a pretty dark grey. It only reflects about 12% of the light that hits it. It is about the colour of (worn) tarmac on the road. You can see how grey it is in NASA's gif from a million miles away.

"Black" paint reflects less light. Common household black paint reflects only about 5% of light. So the moon would be rather less than half as bright as it is now. But you could still see it. There are some specialised black substances that reflect as little as 0.035%. A moon coated in these would actually be hard to see.

White paint and silver paint reflect about 80% of light, so if the moon were white it would be about 7 times brighter, but much less bright than the sun which is about 400000 times brighter than the full moon.

$\endgroup$
6
$\begingroup$

The albedo of the Moon (the proportion of the light that falls on it which is reflected) is about 0.12. The darkest known material is Vantablack with an albedo of about 0.0004. So if you painted the Moon with that, the reflected light level would drop by a factor of roughly 300, taking the magnitude of a full moon from -13 to -6 or so. This is still brighter than the Moon appears when illuminated by Earthshine during a lunar eclipse (about -3), when it is still perfectly visible, so the Moon would not become invisible.

In the other direction, making the Moon perfectly white would increase its brightness 8 fold or about 2 magnitudes, taking it down to -15. This would make moonlight a bit brighter, but probably not change anything fundamental.

$\endgroup$
  • 1
    $\begingroup$ +1 for the comparison to Earth-shine $\endgroup$ – antlersoft Jan 1 at 18:39

Your Answer

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.

Not the answer you're looking for? Browse other questions tagged or ask your own question.