It's a bird… it's a plane… it's a blue meteor? Fireball? Piece of a comet?

Whatever it was, it lit up the night sky for millions of people early Sunday morning in Spain and Portugal. Social media users took stunning pictures and videos for all to revel in the natural science phenomenon.

The spectacular sight crossed the night sky at 12:46 a.m., according to CCTV footage released by the mayor's office in Cádiz. 

The European Space Agency (ESA) Operations says the "blue meteor" everyone is referring to was actually "a small piece of a comet" that flew over the European countries at the speed of 45 kilometers a second, which is equivalent to almost 28 miles. 

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It burned up over the Atlantic Ocean at an altitude of 60 kilometers, or more than 37 miles above the surface. 

"The likelihood of any meteorites being found is very low," ESA Operations tweeted after the agency's Planetary Defence Office analyzed the size and trajectory of the object. 

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National Aeronautics and Space Administration explains the color was likely due to magnesium, and that "meteor color depends on whether the metal atom emissions or the air plasma emissions dominate." 

"Short-period comets, also known as periodic comets, originate from a disk-shaped band of icy objects known as the Kuiper Belt beyond Neptune's orbit, with gravitational interactions with the outer planets dragging these bodies inward, where they become active comets," Space.com states. 

Many on social media referred to what they witnessed as a "once in a lifetime sight," according to news.com.au, with at least one joking, "That’s no meteor, that’s Optimus Prime."

Fox News' Mitch Picasso contributed to this report.