DUNEDIN — Mike Weight was strolling the beach at Honeymoon Island about noon Wednesday when he saw something weird.

A black line appeared against the bright blue sky, shooting down from a cloud into the gulf.

"At first I thought it was an optical illusion because it was like a dark piece of sky with a light sky background," Weight said. "You could see through it."

Maybe it's a waterspout, he thought. That theory faded quickly. This was no funnel cloud.

Confused, the 73-year-old Clearwater resident pulled out his phone and took a couple of pictures.

He emailed them to the Times, attached with a note.

"Any idea what this was?"

Mike Clay, chief meteorologist at Bay News 9, didn't know what the black line was either. He shared the photos with several other weather experts.

One meteorologist came back with a theory: It could be the shadow of a contrail, the stream of condensed water vapor left by a rocket or plane. The contrail could have been concealed by clouds, Clay said.

For such a shadow to appear, conditions need to be just right, with the sun and contrail in precise spots.

But that's just a theory. Clay said no one he spoke with is entirely sure what Weight saw.

"I think we're all just guessing," he said.

What do you think? Have you seen a similar black line in the sky? Do you have any pictures?

Tell us more in the comments section below this post, or email reporter Zachary T. Sampson at zsampson@tampabay.com.

And here are some repsonses from social media:

Aliens. RT @TB_Times It's a funnel cloud! It's a shadow! No it's ... wait; what is it? http://t.co/2gNCh1naFE pic.twitter.com/dnK5PIr2os

@TB_Times looks like a cloud kite!

@TB_Times Sharknado!!