Two asteroids—one very large and one particularly close—will pass close to Earth within 42 hours from Thursday night, according to scientists. Neither will pose any threat, but since one of them was only discovered last week and the other is among the largest ever to pass our planet, they’re a stark reminder of the dangers near-Earth objects pose to the planet.

Fittingly, the asteroids will coincide with the ninth Asteroid Day, an annual festival that includes livestreamed lectures on YouTube that highlight the importance and impact of space on Earth.

2011 UL21: What To Know

When at its closest at 4:16 p.m. EDT (20:16 UTC) on June 27, the asteroid 2011 UL21 will be one of the largest to have recently passed near Earth. Discovered 13 years ago, 2011 UL21 (also known as 415029) is between 1 and 2.4 miles (1.7 and 3.9 kilometers) in diameter. That’s about the size of Mount Everest.

It will fly by Earth on June 27 within 4.1 million miles (6.6 million kilometers) of Earth’s surface at its closest, which is about 17 times the distance to the moon. For an asteroid this big, that’s very close.

Asteroid 2011 UL21 is larger than 99% of near-Earth asteroids. According to the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory, 2011 UL21’s close pass will put it among the top 10 largest asteroids to have passed within 4.6 million miles (7.5 million kilometers) from the Earth in the last 124 years.

The Virtual Telescope Project will livestream on YouTube real-time images of 2011 UL21 through a large telescope. The livestream will begin on June 27 at 4 p.m. EDT (20:00 UTC).

2024 MK: What To Know

Only discovered on June 16, asteroid 2024 MK is between 400-800 feet (120-260 meters) in diameter. That’s about the size of the Eiffel Tower, which is particularly large for an NEO. It will fly by Earth on June 29 within just 180,000 miles (290,000 kilometers) of Earth’s surface at its closest, which will occur at 9:50 a.m. EDT (13:50 UTC), according to NASA. That’s about 75% of the distance between Earth and the moon.

Being so close and so relatively large, 2024 MK will be visible on June 29 to small telescopes. The European Space Agency is making available its NEO toolkit to help backyard astronomers observe it through a small telescope, while The Virtual Telescope Project will livestream on YouTube real-time images of 2024 MK through a large telescope. The livestream will begin on June 29 at 5 p.m. EDT (21:00 UTC).

Asteroid 2024 MK will be one of the brightest objects of its kind seen in recent history, according to Gianluca at the Virtual Telescope Project.

Origin Of ‘Asteroid Day’

The date of the annual Asteroid Day commemorates the Tunguska Event of June 30, 1908, when about 830 square miles (2,100 square kilometers) of Russia’s Siberian forest were flattened, presumably by an asteroid strike. Astronomers have since calculated that Earth was then passing through the Taurid swarm, the remnants of a comet, probably from Comet 2P/Encke, which scientists think may be responsible for some once-per-1,000-years catastrophic events on Earth. The Taurid swarm could also be responsible for a 1,000-year freeze from 11,000 BC and the Tagish Lake meteorite, which fell on Yukon Territory in Canada in January 2000.

Wishing you clear skies and wide eyes.

Pick up my books Stargazing in 2024, A Stargazing Program For Beginners and When Is The Next Eclipse?

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