Some asteroids can 'sneak up' on us thanks to a quirk of the Earth's rotation that makes them seem like they are barely moving — making them hard to detect.

This is the warning of NASA-funded experts who investigated how telescopes nearly missed a 328-feet-wide asteroid that came within 43,500 miles of Earth back in 2019.

In fact, the experts said, up to half of asteroids approaching Earth from a danger zone east of 'opposition' likely undergo periods of such apparent slow motion.

An asteroid is said to be at opposition when its position in the night sky places it along a line that intersects both the Earth and the sun.

Some asteroids can 'sneak up' on us thanks to a quirk of the Earth's rotation that makes them seem like they are barely moving — making them hard to detect (stock image).

Pictured: Some asteroids approaching Earth from the east of opposition (the yellow line) appear at practically the exact same point in the sky as they get closer.

This is because as the asteroid would appear to move eastward across the night sky, such motion is counteracted by the Earth's rotation — meaning it is seen from the exact same angle from the Earth even as it gets closer (represented by the series of parallel, dashed orange lines).

'Near-Earth Objects that approach from a direction east of opposition — most notably 0–2 hours [0–30°] east of opposition — are prone to periods of slow motion during their approach,' the researchers explained in their paper.

'The induced topocentric motion coming from Earth's rotation cancels the natural eastward motion in the sky, making the object appear to be almost stationary, This makes discovery difficult. !

Had the apparent slow motion phenomena not been in play with asteroid 2019 OK, the researchers said, the near-Earth object would likely have been detected up to four weeks before it made its closest approach to our planet.

If any of this meteoroid makes it to Earth, it is called a meteorite