I understand that the redness of the moon during the total lunar eclipse last night/this morning (April 14-15 2014) is a reflection of the red light caused in earth's atmosphere due to Rayleigh scattering (basically, a reflection of all the sunsets and sunrises happening around the earth). Because of this, it seems to me that the moon will appear red during every total lunar eclipse that happens. Is this the case, or are there some lunar eclipses where the moon does not turn red? If it is the case that all total lunar eclipses produce a red moon, why was the media so hyped up about last night's eclipse producing a red moon? Was it especially red?


4 Answers 4


No, not all total lunar eclipses will turn the Moon deep red. Most of them do, but not all.

If you were standing on the Moon during the eclipse, you'd see the Earth passing in front of, and obscuring, the Sun. But the Earth will never become fully dark, even when the Sun is fully covered. A bright ring will always surround the Earth. Why?

That ring is sunlight refracted by the atmosphere. It's there because the Earth has an atmosphere. You could say it's all the sunrises and sunsets of the Earth, all seen at once. It's this light that continues to illumine the Moon during the eclipse.

But why is the Moon red, instead of some other color? This is because the blue end of the spectrum is scattered more easily in all directions (same mechanism that explains why the sky is blue on Earth), whereas the red part of the spectrum is scattered less easily and moves on a straighter path along the refraction lines. The bright ring around the Earth, as seen from the Moon, is probably red, because most of the blue in it has been scattered away.

Now, if the Earth's atmosphere is full of dust particles from huge volcanic eruptions, the bright ring is a lot weaker. That makes the Moon during the eclipse a much darker shade of red. Sometimes the Moon is a very dark, dull grey during the eclipse, no red hue at all - so dark in fact that it's hard to see in the sky while the eclipse is full. This has happened some decades ago after the Pinatubo eruption.




A measure of the brightness and color of a lunar eclipse is the Danjon scale. Eclipses are rated between 0 (almost invisible, black or very dark grey) and 4 (bright orange with bluish rim).



My estimate is that the last eclipse was a 3.

I can't find a list of recent eclipses rated on a Danjon scale, but here's a list of 20th century eclipses, with a measure of the magnitude of the umbra.


As you can see, the magnitude varies quite a bit.

Bottom line: each eclipse is a bit different. A majority would have some kind of orange, copper or red tint. A minority are too dark to see any color. Unusual colors (outside of the red-yellow interval) are very rarely possible. Brightness and hue varies from one instance to another, since it depends on Earth's atmosphere, which is a system that changes greatly over time.

  • $\begingroup$ His question showed that he understands the process, his question was about the degree and the corresponding media attention. Your link to the NASA site has a good reference on the scale of colour, that is a useful addition. $\endgroup$
    – Jeremy
    Apr 17, 2014 at 20:10
  • $\begingroup$ Indeed, I do understand the process. Your information on how volcanic eruptions affect the appearance of the moon was enlightening. Barring volcanic eruptions or some other source of an excess of ash/dust in the air, will the moon always appear red during a total eclipse? $\endgroup$ Apr 17, 2014 at 20:59
  • $\begingroup$ I've added an edit to the reply, expounding a bit on the Danjon scale, umbra magnitude, and variability of lunar eclipses (TLDR: all are different, most are red, a few are too dark to have any color). $\endgroup$ Apr 18, 2014 at 20:06
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    $\begingroup$ Just a point is reflection should not named. Light truly reflected from Earth can be sort of green , blue or white from water, and brown sort from desertic areas most important reflected light cannot it the moon during eclipse. The phenomenon is purely based on the light that goes throughout the atmosphere ( and so does twice, to reach our eyes). $\endgroup$
    – Alchimista
    Feb 1, 2018 at 15:20

Pretty most all lunar eclipses will turn the moon red like that. The amount of redness does vary, and sometimes so little light gets to the sun it is almost completely dark. However the redness is so typical of a lunar eclipse that NASA describes it as a "characteristic orange-red color". That link has a neat table with a categorization of the colour ranges.

Probably what triggered the media's "do a story on that!" bells was lots of chatter they noticed online, mostly from the loony fringe making more of it than it deserves.

The reason for the extra attention was probably because this lunar eclipse (I can't bring myself to write 'blood moon' ick I've done it) is coincident with the Jewish Passover - not a surprising event, as Passover is always when the moon is full after the spring equinox. It happens that the Passover that was celebrated the evening before the day Jesus was executed was followed by a lunar eclipse, and the Bible makes mention of 'the moon being turned to blood.' Simple and straightforward, but then some people start going off on their own weird supposes and imagining that Jesus' second coming will occur on another lunar eclipse, as if a lunar eclipse after the spring equinox was the only time it is possible for him to visit. So you get lots of internet chatter, the media notices what is trending on twitter and does a half-baked story.

Lunar eclipse will occur in other months too, but without this association, people don't seem to care as much.

  • $\begingroup$ "All lunar eclipses will turn the moon red like that." - incorrect. I'll post a more detailed answer below. $\endgroup$ Apr 17, 2014 at 17:19
  • $\begingroup$ Well, I can tweak it some also. $\endgroup$
    – Jeremy
    Apr 17, 2014 at 20:04

The redness of the moon is due to Earth's atmosphere refraction of Sun rays and pollution - dust particles etc. The intensity of the colouring will depend on the path the moon takes through the Earth's corona. If it goes right through the middle then we will see a darker moon, while if it travels close to the edges then the influence of refraction and pollution will be greater and thus a redder moon.


One other aspect: if you are seeing the lunar eclipse too close to sunrise or sunset, with the sky still relatively bright, you can lose the Moon's color. Atmospheric light scattering effectively cloaks the reflected light returning from the Moon (after the atmosphere had refracted the light onto the eclipsed Moon).

But atmospheric scattering is not all bad. In small amounts it can actually give an enhanced contrast. The N9vember 2022 total lunar eclipse came a few hours before sunrise in Chicago, and the view in that city (perhaps aduded by atmospheric scattering of the city lights) looked like this:

enter image description here


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