Strange Portals

A common theme in science fiction is that of the portal through space, time, alternate dimensions, or all three. These strange doorways open up into realms unknown, providing a passage to the outer fringes of our reality and our understanding. Yet, by some accounts these openings through space and time are not merely the domain of science fiction, but actually do exist. One place where such outlandish portals seem to materialise quite often is up in the sky, we can find all manner of reports and even photographic evidence of what appears to be something straight out of a science fiction story.
 
Among the types of portals said to have opened up in the sky are those that seem to be undeniably linked to the UFO phenomenon, with these mysterious craft apparently utilising these doorways for their own purposes. What is your take on this?