A huge asteroid will safely fly by Earth today (March 3), and you can watch it live online.
The Virtual Telescope Project is planning to stream live telescope views of the asteroid 138971 (2001 CB21) during its approach. The space rock is technically classified as "potentially hazardous", but there's no need to worry. The asteroid will pass by at the equivalent of nearly 13 times the average Earth-moon distance (3 million miles, or 4.9 million kilometers), according to the Center for Near-Earth Object Studies (CNEOS) managed by NASA's Jet Propulsion Laboratory.
Asteroid 2001 CB21 measures between 1,800 feet (560 meters) and 0.7 miles (1.2 kilometers) in diameter, according to CNEOS. That's about as big as Chicago's Navy Pier.
The Virtual Telescope Project's event starts at 10 p.m. EST (0300 GMT Thursday, March 4). Typically the project uses a telescope based near Rome, run by founder Gianluca Masi. "The potentially hazardous asteroid (138971) 2001 CB21 will have a relatively close and obviously safe flyby with our planet," Masi said in a statement. "The Virtual Telescope Project will show it to you live, online: join us from the comfort of your home!"
If you're looking for a telescope or binoculars to spot asteroids like this one, check out our guide for the best binoculars deals and the best telescope deals available now. Our best cameras for astrophotography and best lenses for astrophotography can also help you pick the best imaging gear.
NASA keeps its eyes peeled for asteroids using a network of partner telescopes as well as space observations, coordinated through the Planetary Defense Coordination Office. The agency has found no imminent threats yet, but it continues the search to be proactive.
The agency also tests out asteroid defense technologies (not that we need them yet) such as one that will arrive at an asteroid moon very shortly. In late September or early October 2022, the 1,210-pound (550 kilograms) DART spacecraft will slam into a small asteroid named Dimorphos, changing this space rock's orbit around its larger companion, Didymos.
Overall we know of around 750,000 asteroids, but the vast majority don't come anywhere near Earth. Scientists have identified more than 27,000 near-Earth asteroids, with new ones spotted constantly.
Potentially hazardous asteroids are classified as those space rocks over a certain brightness (implying a certain size, although the correlation isn't perfect) that come within 4.65 million miles (7.48 million km) of Earth. (The distance is one-twentieth of the average distance between Earth and the sun.)