In Monterey, California, with a "half-moon" high in the sky at about 9 pm (2017-08-30), the moon had a distinct red outline on the outer edge of the NE quadrant; for awhile I saw it also on the outer edge of the SW quadrant.

I observed this phenomena from two locations, about a mile distant from each other.

I've never seen that before. What would cause it?

I took a picture of it with my camera, but you can't tell anything "out of the ordinary" from the image.


It's a clunky picture (I've been watching My Three Sons lately) - red not visible, fuzzy, and makes it like a full moon, but here it is, at any rate:

enter image description here

  • $\begingroup$ curious.astro.cornell.edu/about-us/46-our-solar-system/the-moon/… -- are you having brush fires or similar phenomena that might make the atmosphere more polluted than usual? $\endgroup$
    – user21
    Commented Aug 31, 2017 at 4:42
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    $\begingroup$ @StephenG: Yes, but I wasn't wearing them at the time; I don't think my wife was wearing hers, either, and she also observed it, although, oddly enugh, she only saw the red outline on the SW corner. $\endgroup$ Commented Aug 31, 2017 at 12:04
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    $\begingroup$ Vertical smoke integration map (US, part of Canada): airquality.weather.gov Active fire map (US): fsapps.nwcg.gov/afm $\endgroup$ Commented Aug 31, 2017 at 12:57
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    $\begingroup$ I'm pretty sure that air pollutants are the reason, like a few have pointed out. Such particles can scatter high wavelength moon light, and make it appear redder. $\endgroup$ Commented Aug 31, 2017 at 13:23
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    $\begingroup$ @B.ClayShannon You can't necessarily feel the smell of smoke in the air, if it's at very high altitude. I live in the SF Bay Area, the sky seems clear now, but when I went to Salem OR to view the eclipse, the sky had a distinct reddish hue, and was even a bit hazy, for days in a row in many parts of Oregon due to the big fires in that state. Could not smell the smoke at all down in the flat areas of the state. When crossing mountain passes at high altitude, I could tell there was a faint smell of burnt wood in the air - but it was just barely there. $\endgroup$ Commented Aug 31, 2017 at 18:44

1 Answer 1


Smoke (fire) is not the only explication - Dust is also a good candidate. I've noticed a drop in "seeing quality" even when observing deep sky objects or planets trough a telescope due to large amounts of dust in the air.

The second reason for a red Moon is if there’s some kind of particle in the air. A forest fire or volcanic eruption can fill the air with tiny particles that partially obscure light from the Sun and Moon. Once again, these particles tend to scatter blue and green light away, while permitting red light to pass through more easily. When you see a red moon, high up in the sky, it’s probably because there’s a large amount of dust in the air.

(source: Red Moon - Universe Today)


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