Artist view of an asteroid passing Earth. Credit: ESA/P.Carril

Big Asteroid 2004 BL86 Buzzes Earth on January 26: How to See it in Your Telescope

Article Updated: 26 Apr , 2016
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A lot of asteroids pass near Earth every year. Many are the size of a house, make close flybys and zoom out of the headlines. 2004 BL86 is a bit different. On Monday evening January 26th, it will become the largest asteroid to pass closest to Earth until 2027 when 1999 AN10 will approach within one lunar distance.

Big is good. 2004 BL86 checks in at 2,230 feet (680-m) wide or nearly half a mile. Add up its significant size and relatively close approach – 745,000 miles (1.2 million km) – and something wonderful happens. This newsy space rock is expected to reach magnitude +9.0, bright enough to see in a 3-inch telescope or even large binoculars.

This graphic depicts the passage of asteroid 2004 BL86, which will come no closer than about three times the distance from Earth to the moon on Jan. 26, 2015. Due to its orbit around the sun, the asteroid is currently only visible by astronomers with large telescopes who are located in the southern hemisphere. But by Jan. 26, the space rock's changing position will make it visible to those in the northern hemisphere. Click to see an animation. Credit: NASA/JPL-Caltech

This graphic depicts the passage of asteroid 2004 BL86, which will safely pass by the Earth on January 26th. Closest approach occurs around 10 a.m (CST) that day. The asteroid is currently only visible by astronomers with large telescopes who are located in the southern hemisphere. But by Jan. 26, the space rock’s changing position will make it visible to those in the northern hemisphere. Click to see an animation. Credit: NASA/JPL-Caltech

This is a rare opportunity then to see an Earth-approaching asteroid so easily. All you need is a good map as 2004 BL86 will be zipping along at two arc seconds per second or two degrees (four Moon diameters) per hour. That means you’ll see it move in real time like a slow satellite inching its way across the sky. Cool!

As you can see from its name, 2004 BL86 was discovered 11 years ago in 2004 by the Lincoln Near-Earth Asteroid Research (LINEAR), an MIT Lincoln Laboratory program to track near-Earth objects  funded by the U.S. Air Force and NASA. As of September 15, 2011, the search has swept up 2,423 new asteroids and 279 new comets.

Map showing the hourly progress of 2004 BL86 Monday evening January 26th as it treks across Cancer the Crab not far from Jupiter. Stars are shown to magnitude +9. The number at the tick marks show the time (CST) each hour starting at 6 p.m., then 7 p.m., 8 p.m. and so on. Click for a larger version. Created with Chris Marriott's SkyMap program

Map showing the hourly progress of 2004 BL86 Monday evening January 26th as it treks across Cancer the Crab not far from Jupiter. Stars are shown to magnitude +9. Numbers at the tick marks show the time (CST) each hour starting at 6 p.m., then 7 p.m., 8 p.m. and so on. Click for a larger version. Created with Chris Marriott’s SkyMap program

All asteroids with well-known orbits receive a number. The first asteroid, 1 Ceres, was discovered in 1801. The 4,150th asteroid, 4150 Starr and named for the Beatles’ Ringo Starr, was found in 1984. 2004 BL86 will likely be the highest-numbered asteroid any of us will ever see. How does 357,439 sound to you?

Some observers prefer a black on white map for tracking asteroids and deep sky objects. Click to view a larger version. Created with Chris Marriott's SkyMap program

Some observers prefer a black on white map for tracking asteroids and deep sky objects. Click to view a larger version. Created with Chris Marriott’s SkyMap program

Observers in the Americas, Europe and Africa will have the best seats for viewing the asteroid, which will shine brightest between 7 p.m. and midnight CST from a comfortably high perch in Cancer the Crab not far from Jupiter. The half-moon will also be out but over in the western sky, so shouldn’t get in the way of seeing our speedy celeb.

Not only will 2004 BL86 pass near a few fairly bright stars but the Beehive Cluster (M44) will temporarily gain a new member between 11 p.m. and midnight as the asteroid buzzes across the well-known star cluster.

“Monday, January 26 will be the closest asteroid 2004 BL86 will get to Earth for at least the next 200 years,” said Don Yeomans, who’s retiring as manager of NASA’s Near Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, California, after 16 years in the position.

More detailed map showing the hourly position of the asteroid through central Cancer. Stars plotted to magnitude +9.5. Created with Chris Marriott's SkyMap software

More detailed map showing the hourly position of the asteroid through central Cancer. Stars plotted to magnitude +9.5. Click to get a larger version. Created with Chris Marriott’s SkyMap software

To learn more about the space rock and acquire close-ups of its surface, NASA’s Deep Space Network antenna at Goldstone, California, and the Arecibo Observatory in Puerto Rico will attempt to ping the asteroid with microwaves to create radar-generated images of the asteroid during the days surrounding its closest approach to Earth.

“When we get our radar data back the day after the flyby, we will have the first detailed images,” said radar astronomer Lance Benner of JPL, principal investigator for the Goldstone radar observations of the asteroid. “At present, we know almost nothing about the asteroid, so there are bound to be surprises.”

NASA's Deep Space Network will be watching during 2004 BL86's flyby Monday Jan. 26. Credit: NASA

NASA’s Deep Space Network will be watching during 2004 BL86’s flyby Monday Jan. 26. Credit: NASA

While 2004 BL86 will be brightest Monday night, that’s not the only time amateur astronomers might see it. It comes into view for southern hemisphere observers around magnitude +13 on Jan. 24 and leaves the scene at a similar brightness high in the northeastern sky in the northern hemisphere on the 29th. If you use a star-charting program like Starry Night, Guide, MegaStar and others, you can get updated orbital element packages HERE.  Just select your program and download the Observable Unusual Minor Planets file. Open it in your software and create maps for the entire apparition.

One last observing tip before you go your own way. Close asteroids will sometimes be a little bit off a particular track depending on your location. Not much but enough that I recommend you scan not just the single spot where you expect to see it but also nearby in the field of view. If you see a “star” on the move – that’s it.

As always, Dr. Gianluca Masi, Italian astrophysicist, will share his live coverage of the event beginning at 1:30 p.m. (19:30 UT) Jan. 26th.

Let us know if you see our not-so-little cosmic friend. Good luck!

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6 Responses

  1. Teamonger says:

    Greetings Bob, nice article. I notice your finder maps differ somewhat from the one in S&T February issue. Your path looks slightly to the west, and your times are behind by about 15 minutes. S&T map has the asteroid passing the center of the Beehive about 05:15 UT, while your map would have it more like 05:30. Are these differences due to the variant earth locations used to draw up the maps?

    • Bob King says:

      Teamonger,
      Possibly. Either that or the orbital elements are slightly different. I used the latest. That’s also the reason I added the caveat in the article about keeping an eye around the spot rather than staring at just one spot.

      • Teamonger says:

        Thanks Bob. What I found interesting in your path are the near encounters with brightish stars along the way: HIP 42010, HIP 42187, and HIP 42673 in the Beehive. The S&T map has the path further away from those. I’ve noted the times, curious to see how close they actually get. Even wonder if an occultation is possible…

      • Bob King says:

        Teamonger,
        Looks like our weather might just be clear enough Monday night. I’m eager for a look. Most of these fast-movers are faint. Amazing how bright this one is for a change.

      • Teamonger says:

        I was clouded out, durn it. Hope to try again tonight for the fainter version in Ursa Major.

      • Bob King says:

        Me too Teamonger! But if you have an 8-inch scope you can track it through the 29th when it’s still just mag. 13.

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