Florence Flyby

By Chuck McPartlin

Early Friday morning, at 05:06:09 PDT for Santa Barbara, a large Potentially Hazardous Asteroid (PHA) named after Florence Nightingale will make a fairly close approach to the Earth.

3122 Florence is estimated to be about 2.7 miles in diameter, based on its reflectivity and assumed surface composition. It is the fourth largest PHA known, with only 53319 1999 JM8 (4.3 miles), 4183 Cuno (3.5 miles), and 3200 Phaethon (3.2 miles) being larger. By comparison, the Chicxulub asteroid that the dinosaurs failed to deflect was estimated to have been about 6 miles in diameter.

Florence’s closest approach will be to a distance of about 4.4 million miles, or a little over 18 times the distance to the Moon. This will be its closest approach since 1890, and in won’t come closer until after 2500. NASA will take advantage of this approach to do detailed studies of Florence with both optical telescopes and radar, so expect some cool images in the next few days.

I took a look at Florence Wednesday, since it was bright enough to be detectable with small telescopes, and even with binoculars from a dark site. I was dealing with moonlight and the Noleta light dome, so the sky background was milky, but Florence was bright enough to stand out. Here’s an animation of its apparent motion for a few minutes at around 11 PM.

You can also see my periodic tracking error, and the hot pixels in the camera, which don’t move with the scene. The occasional fuzzouts and brightenings are caused by our atmospheric turbulence – what your eye sees as twinkling. The animation is made from snapshots of the camera’s video stream every 30 seconds, and the camera was integrating for 8.5 seconds. The telescope was a 5-inch, f/6.3 refractor.