WASHINGTON, Sept. 7 (UPI) -- Two small asteroids will pass by the Earth Wednesday at distances closer than the moon, U.S. astronomers say.

The two asteroids, only recently discovered by astronomers, will not be visible to the naked eye as they cross the Earth's orbit, SPACE.com reported.

While other asteroids have made close Earth passes, it is unusual to have two coming so close at the same time.

The smaller of the two, 2010 RF12, will have the closer pass at about 49,000 miles, while a larger asteroid, 2010 RX30, will pass first at a distance of about 154,000 miles.

The average distance between Earth and the moon is about 238,600 miles.

Asteroid 2010 RF12 is estimated at 19 feet to 42 feet wide, while the larger 2010 RX30 is estimated at 33 feet to 72 feet, a Jet Propulsion Laboratory asteroid database says.

Using a network of telescopes on the ground and in space, NASA routinely tracks asteroids and comets that may approach near the Earth.

The space agency's Near-Earth Object Observations program is responsible for finding potentially dangerous asteroids and studying their orbits to determine if they pose a risk of hitting the Earth, SPACE.com said.