1
$\begingroup$

The question Why does the Moon appear gray when passing between the Sun and the Earth? shows the famous "Moon photobombs Earth" image of the moon in front of the Earth taken from the EPIC camera on DSCOVR. It looks fairly neutral color, as does the image below that, which shows a particular section of the lunar soil to be fairly neutral gray, assuming the spacesuit is also neutral (white).

But the spectrally resolved albedo of the Moon is not even close to neutral! I've seen other spectral albedo plots of the moon from very different observations and they all look the same, about 0.07 at 400nm and almost doubling to 0.14 at 700nm. In a word "orange".

But the full or gibbous moon when high in the sky doesn't look orange to me at night, even when there are various terrestrial sources around to get a color reference, even looking through a window from a well lit room, even looking at it during the day. It always looks essentially white.

Why doesn't a full/gibbous moon high in the sky ever seem to look orange? Shouldn't it?

As a non-scientific enquiry, I took the photobomb image as-is from the question (shown below) and used my computer to color analyze the moon. I got this, which does show a definite progression, blue darker than green darker than red:

enter image description here

enter image description here

If I isolate the moon with Python and calculate the average pixel values in the R, G, and B channels, I get [0.33, 0.31, 0,28] which is a pretty good match to the albedo plot if I just look at the plot around 450, 550, and 650nm, (which is what normal people do after spending hours trying and failing to understand the intricacies of human color perception).

So is the moon really orange? Does it add a substantial orange tint to the reflected sunlight, and we just don't notice it?

enter image description here

enter image description here

above: "Figure 8: Averaged geometrical moon albedos measured by GOME from July 1995, November 1995, and September 1996." From ESA's GOME moon measurements, including instrument characterisation and moon albedo.

Moon photobombs Earth

enter image description here

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

| improve this question | |
$\endgroup$
  • $\begingroup$ A neutral grey color test card looks the same in morning, midday and evening sunlight. But the light is very different, the color temperature is from about 1850 to 7000 K, moonlight is 4100 to 4150 K. It depends on the adaption of the eye if you see this light orange, white or blue. See en.wikipedia.org/wiki/Color_temperature. The foto of Buzz Aldrin was supposedly taken with daylight film for about 5000 K, the difference to moonlight is to small to look orange. But if the light is about 2000 K (morning, evening or candle light), a foto taken with daylight film looks very orange $\endgroup$ – Uwe May 21 '17 at 20:20
  • 3
    $\begingroup$ I suspect that due to the vast dynamic range of human vision, the difference in albedo at different wavelengths registers to the eye as only a slightly warm gray. $\endgroup$ – Russell Borogove May 21 '17 at 21:22
  • $\begingroup$ @RussellBorogove I think you are right. $\endgroup$ – uhoh May 22 '17 at 0:19
  • $\begingroup$ Related: physics.stackexchange.com/questions/138795/… $\endgroup$ – BowlOfRed Oct 4 '18 at 22:14
  • $\begingroup$ I wonder if the red reflection could have something to do with earth's atmosphere reflecting a shadow. When the sun dips below the horizon it gets this reddish color. Perhaps it's the same effect refracted onto the surface of the moon? (Total guess) $\endgroup$ – Magic Octopus Urn Oct 5 '18 at 1:42
1
$\begingroup$

I am surprised this has not already been answered. It makes me feel like I'm missing something, but here goes...

But the full or gibbous moon when high in the sky doesn't look orange to me at night, even when there are various terrestrial sources around to get a color reference, even looking through a window from a well lit room, even looking at it during the day. It always looks essentially white.

Why doesn't a full/gibbous moon high in the sky ever seem to look orange? Shouldn't it?

I am not sure what causes the moon to look always white or grey for you, but the answer is rather simple for me, as it does look orange. Sometimes.

Frequently, when the moon is full I (and others around me) notice and comment on the beautiful colors of the moon. Usually it is a reddish color, but sometimes it is more of an orange. When it is a lighter color, I have heard some people say it is yellow, but it looks more orange to me.

This is not a slight change in color. The color is drastically different and difficult to miss if you are looking at the moon.

So, to answer your question...

Why doesn't a full/gibbous moon high in the sky ever seem to look orange?

It does.

Shouldn't it?

I don't know if it should. I just know that it does, at least here. I am in the northeastern US.

I am sorry you are not able to enjoy this, as it really is beautiful.

| improve this answer | |
$\endgroup$
  • $\begingroup$ nice answer, thanks! ;-) btw I do profoundly enjoy looking at the Moon and appreciate its beauty, and in fact if I think back I may have thought it looked orange when I was younger, then convinced myself it wasn't true because it looked gray on TV (yikes!) $\endgroup$ – uhoh Oct 4 '18 at 20:22
  • 1
    $\begingroup$ Those colors are due to atmospheric effects - the coloration is increased when the moon is closer to the horizon, because light is passing through more of the Earth's atmosphere. The moon seen high in the sky through clear air looks to me to be cold gray. Either the moon is changing color drastically hour-to-hour, or the color is not coming from the moon itself. $\endgroup$ – Russell Borogove Oct 4 '18 at 20:34
  • $\begingroup$ @RussellBorogove I don't think the color I described is limited to the moon being close to the horizon. I seem to recall this being true even when it is at a much higher angle. However, instead of asserting this as truth, I will try to pay attention and check on this. $\endgroup$ – Aaron Oct 4 '18 at 20:41
  • $\begingroup$ @uhoh If what Russell Borogove suggests is the case for my observations, then I apologize as it would not answer the question as you have worded it. I will delete the answer in that case. However, I don't think that it is the case - I will test it out to see for sure. $\endgroup$ – Aaron Oct 4 '18 at 20:43
  • 1
    $\begingroup$ @uhoh You specifically used the wording "when high in the sky," so you very well may have had this in mind when asking the question originally and just not stated it. Anyway, I'll try to remember to set an alarm on my phone to remind me to check on this daily or weekly. If my results seem to challenge the low-altitude atmospheric effects statement, then I'll provide my crude altitude and color data. $\endgroup$ – Aaron Oct 4 '18 at 21:09

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