Florence
Key facts
- What it is
- Near-Earth asteroid with two moons (Amor group)
- Size
- About 4.5 km across
- Discovered
- 1981, by Schelte Bus
- Spacecraft
- Not yet visited
- Orbit group
- Amor
- Average distance from the Sun
- 1.77 au (about 260 million km)
- Time to go round the Sun
- 2.4 years
- Closest and farthest from the Sun
- 1.02 to 2.52 au
- Tilt of its orbit
- 22.1°
- Closest its orbit comes to Earth's
- 6,600,000 km (17 times the Moon's distance)
- Spins once every
- 2.4 hours
An au (astronomical unit) is Earth's average distance from the Sun, about 150 million km. Orbit figures are from open tracking data, figures last updated 1 Nov 2026.
Florence is one of the largest near-Earth asteroids, about 4.5 kilometres across. Schelte Bus discovered it on 2 March 1981 at the Siding Spring Observatory in Australia, and it was named after Florence Nightingale, the founder of modern nursing.
On 1 September 2017 Florence passed about 7 million kilometres from Earth, roughly 18 times the distance to the Moon. It was the closest approach by an asteroid of that size since organised searches for near-Earth asteroids began, and the closest Florence itself will come until after the year 2500. The pass was completely safe, and it gave astronomers an excellent opportunity to study it.
Radar telescopes bounced signals off Florence and made images of it. They showed a rounded body with a ridge around its equator, and a surprise: two small moons, each a few hundred metres across. Only a handful of near-Earth asteroids are known to have two moons, and Florence is the largest of them.
During the 2017 pass Florence also became bright enough for amateur astronomers with small telescopes to watch it creep across the stars over several nights.
Florence is classed as an Amor asteroid, approaching Earth's orbit from outside. Because it is large and its orbit comes fairly close to Earth's path, it is classed as a potentially hazardous asteroid. That label sounds alarming, but it is simply a way of listing objects that deserve continued tracking. Florence's orbit is very well known, and it poses no risk.
Coming close to Earth
Its next passes within about 30 million km of Earth, worked out from its orbit. Each one is a safe miss.
| Date | Distance | In Moon distances |
|---|---|---|
| 2 Sept 2057 | 7,500,000 km | 19 |
| 11 Sept 2097 | 23,000,000 km | 61 |
| 27 Aug 2130 | 13,000,000 km | 34 |
| 28 Aug 2170 | 12,000,000 km | 30 |