A 200-foot-wide asteroid will fly past the Earth this Halloween as a rare Blue Moon appears in the sky.

The space rock, dubbed 2020 UX3, is estimated to measure between 88 and 196 feet in diameter, data from NASA's Center for Near Earth Studies (CNEOS) shows.

This observation, as the unmanned space rock reaches its closest approach to Earth in the next 100 years, is rare: it stands out in the lunar calendar by only a single night.

"In the 4,500-year history of the moon's four-color face, we have only seen two Blue Moons, and this one must be the most exceptional one of all," senior author Chris Warwick of NEOScout, a collaboration of American universities that numbers student scientists and educators for educational outreach, said in a statement. "It's a rare and special event to be able to observe this event." [8 Surprising Lunar Facts]

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The helium-rich and energetic asteroid originated from the Oort Cloud, a super-sized area in the outer reaches of the solar system containing thousands of asteroids, says CNEOS Voyager project manager Steve Kouwenhoven. This leads researchers to believe helium-rich asteroids like 2020 UX3 will fly close to Earth several times each century, usually in October, the rarest month among all the lunar cycles.

So far, the 2020 UX3 has only been observed for just four days, and eight such stars are known to be behind the 6th magnitude star-formation center. The asteroid is also visible to the unaided eye in binoculars, a thought unlikely, according to Warwick.

Given these desirable characteristics, it's notable that we have only observed this unique event a mere six times before.

2017 vs 1992 Blue Moons

No date has been set for 2020's passing by Earth, but scientists have been busy observing the asteroid in several movements over the weeks since XASO realized it could be a Blue Moon on Oct. 15. The asteroid was first spotted on Oct. 19, so the hunt for snow comet nursery began.

"Initially we were not "after" 2020; we were "around" it," Independent Alabama realized team member Trohlyre Simoes. "After three nights, we actually had to 'research'" the object. [Amazing Photos of the Blue Moon]

It only became clear to Simoes & Iracyrdydowni that the moon remained just 36 hours apart over the previous three nights
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