Asteroid QC8 is about 0.62 mile (one kilometer) wide and will be about 5.4 million miles (8.7 million kilometers) away at its closest approach, or 23 times the distance the moon is from Earth. At 625 to 1,400 feet wide (190 to 430 meters), QG42 is smaller, but it will get considerably closer—making it a more significant event for sky-watchers.

QG42 is roughly the size of a 14-story building and is officially classified as a potentially hazardous asteroid (PHA) by astronomers because of its proximity.

(See asteroid pictures.)

At 1:10 a.m. Eastern Time (ET) on September 14, QG42 will pass our planet only 7.5 times farther than the moon's orbit (about 1.7 million miles, or 2.8 million kilometers).

According to orbital calculations, QG42