the earliest blue sky yet

Today I got going down a Rabbinical rabbit hole.

When was the first time someone called the sky blue? I've made the search a minor hobby for years now. I mean an unambiguous claim that *this* color (which we can somehow know is what we'd call blue) is the color of the sky. 

For years, the earliest thing I could find was a heraldic text from the 1350s. But then a double breakthrough happened, when a friend turned me on to a trail that led to the Jewish scholar Maimonides, who, writing in the late 1100s, discusses a recipe for making ceremonial colored cloth (that blue that we still associate with Judaism) — and then to an earlier scholar, Rashi, who wrote in the late 1000s. 

But today. Today! I actually dug in to Rashi, in his note for Numbers 15:41, where he says "the colour תכלת resembles the sky when it darkens at eventide." We know he means blue because we can follow the recipe for the dye and it gives us blue.

And then there's a reference to the Tractatus Menachot, which indeed refers to some ceremonial cloth strings as "sky-blue." 

Wow! The Menachot was written sometime between AD 450 and 550. That takes us back half a millennium.*

* that is, if I can track down the Hebrew text. So far I've only seen a translation, and those are notoriously tricky for things like color. But it may very well be! Wow.

Of course this doesn't change the overall fact that it was well after 1000 that the idea of the sky being blue became commonplace. All evidence points to the fact that people just didn't think of the sky — air, space, light — as something that could be pigmented the way plants and animals and earth are pigmented.

In my search, some years ago, I pointed out to a linguist that, although a blue sky never appears in the Bible's 31,000 verses, Jesus said the sky could be red ("When it is evening, ye say, It will be fair weather: for the sky is red. And in the morning, It will be foul weather to day: for the sky is red and lowering. O ye hypocrites, ye can discern the face of the sky; but can ye not discern the signs of the times?"). My linguist friend looked it up. The Greek word wasn't "red" (kokkinēn), which you'd use for colored things. It was more like "fiery" (pyrrazei: think "pyro").

Once again, we're faced with the idea that it took a long time before people thought of the sky as a thing that you could describe with the color-names you'd use for paint. 

But then a tiny crack. There's an obscure, behind-closed-doors reference to the sky being blue that shows up in the 5th or 6th century, then sits dormant for another 500 years, before there's another mention, just as obscure — tellingly, among Jewish scholars, who are [1] likely to go into numbing detail about things like the composition of fringes on cloth, [2] part of a tradition that uniquely employs blue as a ceremonial color, and [3] in some ways shut off from the larger discourse of the West. 

Then a couple of hundred years later, in the 1350s, it shows up in Bartolo di Sassoferrato's De Insigniis et Armis, where he says that blue "represents the sky" in heraldry. From there, the idea of the sky as something blue spreads. You begin to see it more in paintings. Before 1400, it's hard to find a blue sky in art. Crazy, right? But there it is.

We consider it so obvious that it's a cliche of obviousness. Ask a question with an obvious yes answer, and you may get the sarcastic response "Is the sky blue?!" Obama once said that if he said the sky is blue, his opponents would say it isn't. On and on, you find the blueness of the sky to be the very emblem of Something Everyone Knows. 

And yet we didn't know it until just yesterday.