You've probably seen more than your fair share of stories about UFO sightings. An astronaut on the ISS just has to catch footage of a fireball shooting across Earth's skies, and conspiracy theorists have a field day. Whether it's clouds that look like spaceships or rogue meteors, the internet loves a good alien conspiracy.

But former NASA engineer James Oberg has taken it upon himself to trawl through all the sightings and stories out there and politely debunk them, using science. 

The conclusion? Most of your "insane UFO sightings" are little more than 'space dandruff', or your brain misunderstanding of what space travel actually looks like, says Oberg. 

As Cara Giaimo from Atlas Obscura reports, after working at NASA mission control in the late '90s, Oberg went on to become a space journalist and historian. It wasn't until a few years ago that he started to take UFO sightings seriously.

His goal isn't to simply crap all over true believers - he calls that "stomping on dormice" - instead he's interested in teasing out exactly what's going on in these images and videos, and trying to figure out why people are reacting so strongly to them.

His hypothesis? Our human senses are so used to focussing on relatively slow-moving objects, as well as certain light and atmosphere conditions, that when things change, our brains get confused. 

"Our sensory system is functioning absolutely perfectly for Earth conditions," Oberg told Giaimo. "But we're still a local civilisation. Moving beyond our neighbourhood has been visually confusing."

Some of the most common sighting he has to debunk are to do with NASA astronauts reportedly seeing UFOS and being forced to keep silent, which Oberg says is a result of us watching too much sci-fi and not really understanding what space really looks like.

"I've had enough experience with real spaceflight to realise that what's being seen in many videos is nothing beyond the 'norm' from fully mundane phenomena occurring in unearthly settings," Oberg writes over on his site.

Here are some of the more common reports you might have seen on the interwebs, and Oberg's explanation of what's really going on:

UFO sightings at the International Space Station

The real story? Space dandruff, which are things that have shed off space vehicles during flight, like ice flakes, paint chips, or fragments of insulation. They're different to space junk, because they don't pose a real threat to spacecraft, Oberg explains on his site.

These flecks of dandruff are pretty common, but the reason they look so weird to us is that we're not used to the way these objects look when they fall while the space station is travelling through space.

It's the same reason why people see so many UFOs in the footage filmed by the cameras attached to NASA's old space shuttle missions.

In these videos, people usually freak out because the spots seem to dance in and out of view, or suddenly appear and disappear. Which is pretty creepy if you're sitting at your computer on Earth, but isn't that weird if you're on a space shuttle travelling 28,000 km/h (17,500 mph) - nothing's going to stay in your frame of vision very long.

And if the spacecraft is in the right position in relation to the Sun, it can also cast its shadow onto these objects to make them disappear and reappear, which is known as 'twilight shadowing'.

That weird Californian flare across the night sky

At the end of 2015, people in southern California freaked out when they saw a bright white light shoot across the night sky. 

But, as was cleared up pretty soon after the incident, it was actually the result of a planned, unarmed missile test by the US Navy. That strange looking trail of light was the plume of particles blasted out by the rocket thruster.

So why did it look so creepy to everyone else? Because here on Earth, we're used to seeing thin vapour trails left by planes, or billowing smoke plumes. But most of us have rarely (if ever) seen anything so big and sharp as this. 

"There were thousands of people who were absolutely processing their visual stimuli correctly if [the plume] was a mile away or 10 miles away [16 km]," Oberg told Atlas Obscura. "But it was 300 miles [482 km] away, up in space and sunlit, which never occurred to them, because this is not something within the normal range of human experience."

All of this isn't to say we should give up on sharing our UFO sightings, or assuming that everything is 'normal'.

"It's good to keep scanning space video for possible anomalies and reporting them quickly," Oberg told The Huffington Post back in 2013.

"The reason is, there is always a real chance that it could be a genuine anomaly, either a spacecraft malfunction or other threat, expected or unexpected. In the past, missions have failed because a clue that should have been seen out the window was overlooked."

Head over to Atlas Obscura to read the full interview, and more debunkings, with Oberg.