Asteroid 2004 BL86 Buzzes Earth

2004BL86A small asteroid flies past Earth tonight and grows bright enough to spot with a small telescope. The little rock, which is about 300 meters across, was discovered about ten years ago and has the designation 2004 BL86. At its closest approach, the asteroid will pass within 1.2 million km, about three times the Earth-Moon distance. It’s the largest such asteroid to come this close to Earth until 2027.

The brightness of 2004 BL86 will peak between 1h and 6h Universal Time on January 27th as the little rock passes through the constellation Cancer. It will reach about magnitude 9.2, easy to see in a 3-inch or larger telescope. The timing and position favors observers in North and South America, Europe, and Africa.

Solar-system astronomers will be out in force observing this asteroid to get a better idea of composition, size, shape, and surface features. Radar images from NASA’s Goldstone radio telescope will examine the asteroid with a resolution of just 4 meters, so some good images should be available over the next few days.

In a broadcast this morning at, a NASA scientist presented on his cell phone a short video showing radar images of the asteroid taken just last night showing surface detail on the asteroid as well as a small moon (see below):

If you’re a hands-on stargazer, and you want to see the asteroid for yourself, it will pass across a fine star field that includes the famous Beehive Cluster, Messier 44, in Cancer. The asteroid will appear to move at a rapid clip, about 2.5° per hour or about 2.5 arc-seconds per second. That’s enough to see easily from moment to moment as you look through a telescope. The map below from will help you prepare to see it. They also have a good black and white map at this link suitable for printing and bringing along with your telescope.


Asteroid 2004 BL86 passes the Beehive Cluster, M44. The faintest stars in this chart are magnitude 9.2. The dashed circle is 1½° across. Tick marks along the path are given in Universal Time. Credit: