Asteroid Florence will fly by Earth on 1 September at a safe distance of seven million km or "18 Earth-Moon" distances. Florence is about 4.4km wide and is known to be one of the largest near-Earth asteroids according to Nasa. Near-Earth objects are heavenly bodies that enter the Earth's neighbourhood influenced by the gravity of nearby planets.

Paul Chodas, manager of Nasa's Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory in Pasadena, California, stressed the significance of this event when he said, "Florence is the largest asteroid to pass by our planet this close since the Nasa program to detect and track near-Earth asteroids began."

There have been closer fly-bys of asteroids before, but this event is important, said Chodas, because of the size of the asteroid. Other asteroid that have passed even closer to Earth earlier were all estimated to be smaller, he said.

Scientists will make use of this opportunity to study Florence up close. It will be an excellent target for radar observations from the ground, according to Nasa. Observations are being planned from Nasa's Goldstone Solar System Radar in California and at the National Science Foundation's Arecibo Observatory in Puerto Rico.

Through the observations made, it will be possible to get a more accurate picture of Florence as well as detailed images of surface features that are as small as 10m across.

The 1 September fly-by will be the closest Florence has ever come to Earth since it was first spotted in 1980 and it will not get this close again until about 2500. Using deep space radar, scientists will also be able to get a more accurate picture of the size and variations of Florence's orbit as well as its surface roughness, rotation and other vital information, according to a report by Nasa.

Florence can be viewed from Earth for a few days late in August and early September, says Nasa, brightening to its ninth magnitude — magnitude being the measure of brightness of a celestial object as seen from Earth; the lower the number the brighter the object. As it reaches ninth magnitude, it will be visible passing by constellations Piscis Austrinus, Capricornus, Aquarius and Delphinus even with small telescopes, according to Nasa.

While Florence will fly by at a safe distance from Earth, not all asteroids fly clear of our planet's path and scientists have set up several ways to protect our planet from colliding with them. Recently, Nasa unveiled plans to prevent asteroids large enough to cause damage from reaching Earth. The Dart programme involves firing a spacecraft the size of a refrigerator at a speed nine times that of a bullet to directly collide with asteroids to deflect them from its path towards Earth.

There is also a planetary defence network in place that is constantly monitoring and running simulations of events that involve "potential impactors", but even then it is not always possible to be prepared for a fly-by of large asteroids.

Nasa recently offered jobs to people willing to be planetary protection officers.