Our moon is illuminated by our sun, and we can only see it when it’s being illuminated. So, why do we see what looks like shadows, valleys or seas?
Wouldn’t an irregularly surfaced sphere look the same from any angle when illuminated by the same light source?
I’m sure this is elementary physics, but I just don’t see why the reflected sunlight from our moon would show areas of lower light.
What am I missing?
I am not an Astronomer but there are at least two reasons that the moon is not a uniform bright circle in the sky:
Some of material on the moons surface is just generally darker than other bits. You don’t expect an outcrop of dark basalt rock to reflect the same light as a sandy beach so why should it be different on the moon. The lunar “seas” are just darker than the highlands.
You’ve already answered it. The higher ground - mountains, crater edges etc. all cast shadows when the sun is not directly above them.
No–there would be shadows unless it was equally illuminated by that light source from every angle.
The Moon is just like any other visible object that is not itself a light source – we see it because it is reflecting light from some light source. So we see shadows on the Moon for the same reason we see shadows on any other object.
I had to read the OP a dozen times, but I think he might be wondering why we see the shadows at all.
The main (only?) time one would not see shadows is when the light source is coming from the same direction as your vision. For example, if the light source is right between your eyes, you’d see almost no shadows at all. And if you would be standing by the sun and looking at the moon, I think you’d also see no shadows at all. But when we look at the moon from the Earth, and the sun is elsewhere in the sky, then the shadows are easy to see.
Yes indeed, I think the OP is under the misconception that the moon is lit up by the earth. It is, but only to a very small degree. Most of the light is coming from the sun.
Hmmm… If I am correct, then there should be very few shadows and features visible during a lunar eclipse. I do know that the moon IS visible during a lunar eclipse, and it is a verydull brown, and it IS being lit up by what reflects from the Earth. But I don’t remember how well any features are visible then.
Okay, I just looked on Google Images for “lunar eclipse” and for “moon”. I think it is safe to say that VERY few features are visible during a lunar eclipse. Basically, there are only two colors: Brighter, for the jagged mountains, and duller, for the flat “seas”. This can easily result from different degrees of reflectivity. But In sunlight, many individual features can be seen because of the shadows made by the sunlight, and all of that is invisible when the earth is the only light source.
The lunar maria are not darker because they are in shadow. They are darker because they are actually honest-to-goodness darker material than the rest of the moon.
The “seas” are darker material.
The shadows are visible because the light source (Sun) is not in the same direction as our line of sight. Except at full moon, when it’s very close (the Sun is right behind the Earth), so we don’t see any shadows and it’s hard to make out many features.
I hope the OP comes back to tell us whether this answered his question or not.
I had not taken into account the different reflective properties of the various areas on the moon. I’ve always seen it as a homogenous relatively flat surfaced sphere. I didn’t think anything would be tall enough on it to cause such visible shadows over such great distances.
I see that I did word part of that poorly, and thankfully I am aware that the moon is illuminated by the sun and not the Earth.
The reflective properties of the seas was the answer I was looking for.
Nope, which is the reason why the surfaces of stealth fighters are angular rather than rounded. Because of the angles, less of the radar is reflected back.
I found this pair of pictures online that show the same crater at full moon vs. half moon. At half moon, the moon is lit from the side (~90 degrees away from line of sight), so we can see shadows. At full moon, the sun is right behind us, so we can’t see any shadows.
Not only is the moon’s surface uneven in color and altitude (being heavily cratered – I have to say I’m surprised no one, especially today, didn’t realize this), but most of the lunar regolith is fairly dark gray.
Also, areas of meteoric impacts made of iron, or other metals, have introduced a subtle bit of orange or green color in areas where oxidization or volcanic processes occured. Google Apollo 17 + regolith, if curious. There’s heaps of images and info out there.
Now that was enlightening ( pun intended)!
Read more, talk less.
I read it just fine:
It kind of goes without saying that irregular surfaces cast shadows depending on the incidence of light. Didn’t mean that to come off as condescending, I just figured maybe you never really took he time to actually look at the moon or something?
I’ve heard it described as having the albedo of coal. But it does typically contrast sufficiently with the surrounding sky (even during the day when it is gibbous).
The comparison I’ve heard is that it has the same reflectivity as an asphalt car park. But compared to space, that’s still pretty bright.
That’s what I’ve heard as well. Photos and video of the moon (or moon rocks) can be deceiving, so I’ll have to go with the descriptions of the 12 men who’ve actually been there, and the scientific data and measurements on its albedo tell us, as the color/reflectivity of asphalt and charcoal can vary. Needless to say, it’s fairly dark.
If it were as white as limestone, I’ve seen estimates of its magnitude being as bright as -14 (at full moon, it’s -12.6. The sun is -26.7). So around what, 10–15x brighter than it currently is?