Very true. Good point.

I posted this comment several years ago and just found it again. I’m now laughing at my own highly opinionated response, though I still like the idea that the mysterious subject of this poem is not necessarily a hummingbird. Dickinson, characteristically, left the subject unnamed, so I think that in tribute to her, we shouldn’t really make hard and fast “for all time” interpretations of the subject. We become less imaginative when we’re too rigidly determined to solve the mystery.

This seems unlikely to me, since “evanescence” means to disappear quickly, a characteristic not normally associated with a rising sun.

> on certain mornings the sun rises with a brief flash of green,

This flash is much more commonly associated with the setting sun (as illustrated recently in the film, “Pirates of the Caribbean – At World’s End”).
Also, “Resonance” usually means a deep richness, not a brief flash.

> the ball of the sun appears to contain a revolving wheel as it begins to
> emerge above the horizon

I can find no reference to anyone describing this phenomenon on the internet.

> And all the flowers, do indeed, turn their heads to follow its passage

Only a few types of flowers (sunflowers, buttercups) follow the sun.

> And, this bright chariot, could indeed, deliver the mail from Tunis

But not in “an easy morning’s ride” (unless you live within 4 hours of Tunis).

Perhaps your poetry professor was pulling your leg, or was just pushing too hard to find a deeper meaning than was there. This poem is pretty universally accepted to be about a hummingbird. Also, it describes a hummingbird.