Also thank you for answering

To be honest I thought it was the sun and the dev just forgot to/hasn't fixed it yet lmao.

This UFO has been in the game for ages now, always flying sideways. Since in 1.7.6, when the telescope was added, Blago pulled off a prank and put his discord profile picture on the UFO, just to annoy his discord server mods more, as they already were swarmed with people asking about that 'weird light in the sky'.