Yoel and the red moon

As a brief followup to a previous post, what is peshat in Yoel? I am not considering the Zohar here -- I have still not seen it inside, but would still guess a moon, rather than Mars, was intended. But in the pasuk in Yoel, what is the moon that looks like blood?

In Yoel 3, the continuation of the famous pasuk we cite in the Hagaddah:

ג וְנָתַתִּי, מוֹפְתִים, בַּשָּׁמַיִם, וּבָאָרֶץ: דָּם וָאֵשׁ, וְתִימְרוֹת עָשָׁן.	3 And I will shew wonders in the heavens and in the earth, blood, and fire, and pillars of smoke.
ד הַשֶּׁמֶשׁ יֵהָפֵךְ לְחֹשֶׁךְ, וְהַיָּרֵחַ לְדָם--לִפְנֵי, בּוֹא יוֹם יְהוָה, הַגָּדוֹל, וְהַנּוֹרָא.	4 The sun shall be turned into darkness, and the moon into blood, before the great and terrible day of the LORD come.

About a Zohar passage, in a comment on a previous post, Joe in Australia noted:

a "blood moon" would be a lunar eclipse, when the moon is shadowed by the earth and is lit only by light refracted through the earth's atmosphere. It really does look copper-red.

and also that

Solar and lunar eclipses are linked - if the conditions are right for a solar eclipse, there is a good chance that they will be right for a lunar eclipse exactly half a month later. I haven't looked at Yoel 3 inside but a naive reading is certainly consistent with solar and lunar eclipses.

Here is a good explanation of why eclipses happen at particular times. If there is a solar (lunar) eclipse while the moon is traveling towards a node, then the moon will be near the opposite node half a month later and there will be a subsequent lunar (solar) eclipse at that time.

That solar and lunar eclipses are linked is useful considering the linkage in the pasuk,


On this pasuk, Rashi is not so helpful. He merely comments about the sun:

shall turn to darkness: to embarrass those who prostrate themselves to the sun.

But we have Ibn Ezra, who writes:

ג, ד]
השמש -
יספר קדרות שיהיה לשמש בהתחברה עם הירח והירח יקדר ויהיה אדום, זה יהיה בהיותו רחוק מראש התלי וזנבו קרוב משש מעלות, ולעולם הם אותות על מלחמות, והיה לאות כי ימותו עמים רבים.

Thus, it is discussing the darkening of the sun, as it joins {?} with the moon, and the moon darkens and becomes red. This is when it is less than six degrees distant from the head of the dragon or its tail {thanks to Joe in Australia, and Milhouse, in the comment section; see there}. And they are always signs about wars, and it is a sign that many nations will perish.

Obviously, I am way out of my element when it comes to astronomy, as should be clear from my translation above. Anyway, Radak writes what is pictured to the left, and he speaks about degrees of darkness, and how at a certain not-entirely dark stage it is red.