Asteroid Florence will safely pass by on September 1, 2017, coming about 4.4 million miles (7 million kilometers) from Earth. That’s about the distance from the Earth to the Moon 18 times over.
Measurements from NASA’s Spitzer Telescope show that Florence is one of the largest near-Earth asteroids, measuring about 2.7 miles (4.4 kilometers) in size. And it is the largest asteroid to pass by Earth since NASA began characterizing and tracking near-Earth asteroids.
The asteroid is coming close enough to Earth for ground-based radar observations. The radar images are currently planned to be taken with NASA’s Goldstone Solar System Radar and the National Science Foundation’s Arecibo Observatory. These images, which will see down to scales of 30 feet (10 meters), could give us more details about the asteroid, including another size measurement and some surface detail.
Amateur astronomers who want to spot Florence (named for Florence Nightingale) in a small telescope can see it at about 9th magnitude now through early September.