The Pennsylvania State Memorial is silhouetted against the waning light of the sunset on June 16 in Gettysburg. ( Harrison Jones via Twitter )

First things first — it’s not aliens. But it definitely looks like the shadow of a mother ship landing somewhere over Pennsylvania.

The photo above was captured by Harrison Jones from the Pennsylvania State Memorial on Saturday evening. The sunset is a deep orange, and the sky would be almost entirely red had it not been for the strange shadow stretched from the horizon.

It was seen farther south, too. Another reader sent this photo from Westminster, Md., around the same time.

Sunset on June 16 from Westminster, Md. (Erin Bender Thomas)

The explanation is simply perspective. There was a very tall cloud — probably a cumulonimbus — that was building right along the horizon as the sun was setting. Instead of the cloud casting a shadow toward Earth, like it would had the sun been overhead, it was casting the shadow upward.

Clouds are just giant floating blobs in the atmosphere. They have a top and bottom and two sides. Like boxes or spheres, you can create shadows by shining a light at them — and where the shadow lands depends on which way the light is pointing.