asteroid florence
© NASA / JPL-Caltech
Asteroid Florence will pass by Earth on Sept. 1, 2017, at a distance of 4.4 million miles (7 million kilometers).

A large rock will fly past Earth on Sept. 1, 2017, at a distance of 4.4 million miles (7 million kilometers). Asteroid 3122Florence, named after modern nursing founder Florence Nightingale, is the largest object to make a close-encounter since NASA began tracking near-Earth objects (NEO) in the 1990s.

"While many known asteroids have passed by closer to Earth than Florence will on Sept. 1, all of those were estimated to be smaller," said Paul Chodas, manager of NASA's Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory in Pasadena, California.

Florence is estimated to be about 2.7 miles (4.4 kilometers) in diameter. Were an asteroid of that size to strike Earth, it would have worldwide effects. However, this particular rock is not expected to present a risk of collision with the planet anytime soon as its next close approach will not be until after the year 2500.

The Sept. 1, 2017, approach will allow scientists to study the asteroid with radar from the surface of the Earth. Amateur astronomers might also be able to get a peek at Florence, which will have an apparent magnitude of 8.5 and move through the constellations Piscis Austrinus, Capricorn, Aquarius, and Delphinus.

3122 Florence was discovered in 1981 by astronomer Schelte Bus from the Siding Spring Observatory in Australia. It has an orbital period of about 2.4 years with its distance from the Sun ranging from 1.0 to 2.5 astronomical units (one AU is the average Earth-Sun distance: 93 million miles or 150 million kilometers).

Asteroids pass close to Earth all the time. Earlier this year, a 10-foot (3-meter) wide NEO known as 2017 EA passed by at an altitude of just 9,000 miles (14,500 kilometers), well within the band of geostationary satellites at 22,300 miles (35,900 kilometers). It was detected just six hours before its closest approach.