See Florence, One Of The Largest Near-Earth Asteroids, Zip By Earth

The first images taken of the asteroid 3122 Florence with the NASA’s Goldstone radar dish. The smallest details are about 246 feet (75 meters) across. Credit: NASA/JPL-Caltech

We have a wonderful opportunity in the coming week to see 3122 Florence, a 2.7-mile-wide (4 km) asteroid, safely pass about 4.4 million miles (7 million km) from Earth. The fun begins tonight through early next week. Normally, these guys are tiny and faint and require a lot of skill and an 8-inch or larger scope to track. 3122 Florence is different. It’s much larger than the usual Earth-approacher and will come close enough to be visible in even a small telescope. How cool is that?

Florence is a rocky asteroid with an orbit that causes it to pass relatively near Earth on occasion, earning it the designation of PHA or potentially hazardous asteroids. We needn’t worry just yet. No impact is in the cards yet. It’s estimated that 93% of the big PHAs, those measuring 1 km or more, have been discovered.  Credit: NASA/JPL-Caltech

Some of you may even see it in binoculars. For the next few nights, Florence will shine at magnitude 8.7, an easy catch in a 3-inch telescope if you know just where to look. The asteroid will also be moving along fairly quickly, so you’ll know if you have the right “star” if in 2-3 minutes, you see it move in relation to the background stars. Florence will stay in view as it fades to around magnitude 10 in a week. While it will be moving more slowly then, the small-town-sized asteroid will still be a cinch in a 4-inch or larger scope.

Italian astronomer Gianluca Masi captured this view of 3122 Florence on August 28th (dot in center). Like nearly all asteroids viewed in a telescope, it looks like a star. The trail at left is from AMC-14, a geostationary communications satellite. Florence comes closest to Earth around 7 a.m. CDT (12:00h UT) September 1st. Credit: Gianluca Masi

Discovered in 1981, this is the closest Florence, named for Florence Nightingale, the founder of modern nursing, has come to Earth since 1890. It won’t have a closer approach until after the year 2500. This rare opportunity means that NASA’s Goldstone radar dish and the big Arecibo radio dish will be focused on the asteroid before, during and after the flyby. By bouncing radio waves off the surface of Florence and measuring what it reflects back to the antenna, astronomers should able to resolve features as small as 30 feet (10 meters) on its surface,  determine its precise spin rate and better define its orbit. We already have one set of images from Goldstone and I’ll post more as soon as they’re available.

This map shows Florence’s track in the coming week as it zips from Aquarius into the Northern Cross. Its position is shown for 10 p.m. Central Daylight Time each night. Created with Chris Marriott’s SkyMap

Tonight (August 30th), Florence will lie near the 4th magnitude star Nu Aquarii above the “lazy triangle” Capricornus the Sea-Goat in the southern sky. But it quickly picks up speed in the coming nights, heading north-northwest past the nose of the little dolphin constellation, Delphinus and then into Cygnus the Swan (a.k.a. Northern Cross). Although the moon is getting brighter as it waxes toward gibbous phase, Florence moves north and out of its way.

Use this detailed map to track the asteroid through September 1st. Stars are shown to magnitude 9.5 and positions marked every 6 hours in UT. Created with Chris Marriott’s SkyMap
Use this detailed map to track the asteroid through September 3rd UT. Stars are shown to magnitude 9.5 and positions marked every 6 hours. Created with Chris Marriott’s SkyMap
Use this detailed map to track the asteroid through September 4th UT. Stars are shown to magnitude 9.5 and positions marked every 6 hours. Created with Chris Marriott’s SkyMap

You can start your asteroid hunt around 9:30 p.m. local time. A word about the maps I’ve provided. The vertical strip map shows the asteroid’s position at 10 p.m. CDT on each date, but the detailed maps show its location every 6 hours in Universal Time or UT. To convert UT to Eastern Daylight, subtract 4 hours; 5 hours for CDT; 6 hours for MDT and 7 hours for PDT. For example, 0h UT August 31st = 7 p.m. CDT August 30. Or September 1st at 6h UT = 1 a.m. CDT September 1st.

To find the asteroid, print out the appropriate map, then interpolate between the marked positions for the time you plan to observe it. Set up your telescope with a low-power eyepiece and use the map to star-hop to the asteroid’s position. The detailed maps show stars to magnitude 9.5.

If it’s cloudy all week or you don’t have a scope, Gianluca Masi will be live-streaming the speedy visitor starting at 2:30 p.m. CDT (19:30h UT) on Aug. 31 on his Virtual Telescope Project site. Happy hunting!