For whatever reason, I had in mind that the common verb used to describe a rainbow's "state" is bent, as in "a rainbow bent over the landscape".
However, I just Googled "rainbow bent over", and there are really a small amount of results. Googling "rainbow * over" didn't help me understand what's the common verb, as well.
What's the common verb to describe a rainbow? perhaps it's "arch? maybe "stretch"? something else?
I don't think there's a 'common' verb in use for that purpose. 'Bent' is certainly an accurate description and gets the idea across. However, there are some reasons you might not use 'bent'. There is a subtle connotation to the word 'bent' that suggests the thing you're talking about was once straight and might be straight again. It's a term more suited to a solid object than the shape of something as big, beautiful and ephemeral as a rainbow.
The term that comes to mind for me is 'arched'. That word has a more structural, graceful and poetic connotation and better describes the majestic, inspiring sight of a rainbow in the sky. I think most people would think of using 'arched' before they thought of 'bent' or any other description.
Arch sounds best to me, though there’s nothing unidiomatic about bend. Both are used in this Washington Post article in captions:
Rainbow arched across the sky in Gainesville, Va., on Tuesday evening, with a Washington Nationals hat in the foreground.
A rainbow bends over the Capitol on Tuesday evening.
