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I wish I could attach a good quality photograph of this red color moon I'm looking at right now.

I searched on internet but there was no lunar eclipse scheduled to occur on 23rd December 2018

in HYDERABAD, INDIAN SUBCONTINENT around 7:20pm Please tell me why the moon is red tonight:) ?

enter image description here

enter image description here

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  • $\begingroup$ @Chappo The only thing I realize here is that the only person who was able to answer my question actually did understand what my point was, that what I was trying to convey. I was not claiming that it is a lunar eclipse, my question did not end with the line saying "tell me why a lunar eclipse occur tonight?" My point was that I've always seen a red blood moon during an eclipse that's all but I know that doesn't mean that every red moon is a result of an eclipse. I apologize if my way of asking the question was misleading. $\endgroup$ – Human Dec 24 '18 at 6:05
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    $\begingroup$ I understood your question perfectly. What you might not have realised is that someone was trying to close your question, and I was arguing that your question was perfectly valid and should be allowed to remain on our site. :-) $\endgroup$ – Chappo Dec 24 '18 at 7:19
  • $\begingroup$ I really don't understand why would anyone try to close this question... It's perfectly valid and sufficiently related to astronomy. $\endgroup$ – Tosic Dec 24 '18 at 8:00
  • $\begingroup$ Rather than blue being absorbed is correct to say that blue is diffused in random direction. More reddish light propagates easily (in comparison to the "blue" ones) and this effect is noticed when the source (with sun it is the same) is low on the horizon, as for there is a thicker optical path. In case of eclipse, In the moment the light hitting the moon is just that passing through the earth atmosphere, the reason is the same and can get emphasized as it happens "twice" : reddening of the sunlight hitting moon than reddening of the light reflected back to us. $\endgroup$ – Alchimista Dec 24 '18 at 10:00
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    $\begingroup$ @Chappo I plead guilty to the vote, and have removed it. $\endgroup$ – Carl Witthoft Dec 24 '18 at 17:36
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First of all there could not be an eclipse on December 23rd because that is one day later than the full moon.

There can be a couple of reasons for the moon looking red or orange:

  1. It is near the horizon, and being viewed through the atmosphere over a large city. Air pollution (for example from cars, trucks, fires etc) push small sooty particles in to the air. These particles scatter blue light more than red, so there is less blue light coming towards you directly from the moon.

  2. Sometimes sand from deserts can get blown up into the atmosphere, and it can get carried a long way. The sand has a similar effect to the soot.

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  • $\begingroup$ The OP said lunar eclipse $\endgroup$ – Ingolifs Dec 23 '18 at 19:01
  • $\begingroup$ @Ingolifs what's your point? Have you any citation to show a lunar eclipse can happen away from a full moon? $\endgroup$ – Carl Witthoft Dec 23 '18 at 20:17
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    $\begingroup$ There is also a volcanic eruption going on in Indonesia, but I suspect that has not had time to have much effect on the atmosphere. $\endgroup$ – Rob Jeffries Dec 24 '18 at 8:18
  • $\begingroup$ @Rob J - good point $\endgroup$ – Dr Chuck Dec 24 '18 at 9:24
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    $\begingroup$ In principle you don't need any pollution oxygen and nitrogen suffices. Pollution can emphasise the effect as well a scattering in the Mie regime can also occurs. Particulates should do this rather than Rayleigh scattering. Tough In the current case the moon is high enough to require some particles of sort, this is correct. Else we will have red moon every night. Comment about volcano is interesting. ..but it seems far away and time limited. $\endgroup$ – Alchimista Dec 24 '18 at 10:19
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@Human Interesting question. I am editing my answer to remove the old post that may be misleading for new readers.

@Human, @uhoh makes good points. Moonrise was 6:34pm on December 23th in Hyderabad. Azimuth 70.5 degrees (i.e. approx ENE), and altitude approx 9.2 degrees above the horizon. Therefore the moon was likely too far due north from the Krakatoa volcanic plume to be a reddening factor. The reddish moon in the picture that @Human posted is likely due to the effect of the thick atmospheric layer that the moon's light had to travel through at that low angle, over the city of Hyderabad - I don't know much about the condition of air pollution/dust in that area, but @Wayfaring Stranger noted that air pollution was high on Monday 24th Dec. Thank you @uhoh for your helpful comments. Position of moon over Hyderabad on 23 December 2018

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    $\begingroup$ Thanks for your answer. It's interesting but there are some big technical problems. 1) the biggest effect should be the local atmosphere between viewer and the Moon, and Florida's sky is unrelated to Hyderabad's. 2) Light from Sun illuminating Moon only passes through Earth's atmosphere around the time of a lunar eclipse. Here the light passes through space, thousands or probably tens of thousands of kilometers away from the Earth. 3) Your images are from different telescopes and so different cameras, no reason to expect them to be comparable, no evidence they've been calibrated correctly. $\endgroup$ – uhoh Dec 25 '18 at 23:45
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Judging color from snapshots can be a little tricky sometimes but I'm sure in this case the moon was quite reddened by atmospheric effects (normal Rayleigh scattering plus pollution, both natural and artificial). Reddening of the Moon is no different than reddening of the Sun. We may not notice it happening to the Sun until it becomes extreme near the horizon because the same sunlight is also illuminating everything else around us which re-adjusts our internal "white balance" mechanisms.

The Moon isn't actually white or gray in color, it's a bit orange in reality. Here's a plot of the Moon's spectral albedo; it's average reflectivity as a function of wavelength. Our visual sensitivity is strongly peaked in the middle (yellow/green) so the linear slope has less of an impact than we'd expect, but it's still there!

(most of the rest is borrowed from Why doesn't a full/gibbous moon high in the sky ever seem to look orange? Shouldn't it?

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

above: "Moon photobombs Earth" photo from DSCOVR, widely circulated NASA public domain image, from Why does the Moon appear gray when passing between the Sun and the Earth?


As a non-scientific enquiry, I took the photobomb image as-is 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).

enter image description here

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Particulate air pollution was quite high in Hyderabad on Monday. 181 particulate Monday vs the usual 98. The link doesn't seem to say what the units are, but it does say it's all particulate, and that it is "excessive pollution". Note that the contents of this link probably change on a daily or hourly basis. Is this the time of year when the rice farmers burn the stubble in their fields? If so, it's probably smoke making the moon so red.

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During a total lunar eclipse, Earth completely blocks direct sunlight from reaching the Moon. The only light reflected from the lunar surface has been refracted by Earth's atmosphere. This light appears reddish for the same reason that a sunset or sunrise does: the Rayleigh scattering of bluer light.

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    $\begingroup$ The question was quite explicit: there was no full Moon that night. Please ensure you read the question carefully before attempting an answer. $\endgroup$ – Chappo Dec 24 '18 at 7:14

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