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Friday, January 23, 2015


Seeing the Close Flyby of NEO 2004 BL86 26 - 27 January, 2015

The position of asteroid 2004 BL68 as seen at astronomical twilight on the morning of 27 January 2015 (4:50 am ACDST, one and a half hours after sunset) from Adelaide. Click to embiggenThe position of asteroid 2004 BL68 as seen at astronomical twilight on the morning of 27 January 2015 (4:50 am ACDST, one and a half hours after sunset) from Adelaide. Click to embiggen
Printable black and white horizon chart facing west an hour and a half before sunrise on the 27th showing the location of 2004 BL86 as seen from Adelaide. Similar views will be seen from Southern Hemisphere locations at the equivalent local time. Click to embiggen and printPrintable black and white binocular chart an hour and a half before sunrise on the 27thshowing the location of 2004 BL86. The large circle is approximately the field of view of 10x50 binoculars. The small circle the approximate filed of view of a 25 mm eyepiece with a 114 mm Newtonian telescope. Click to embiggen and print

Near Earth Asteroid  2004 BL68 will  come close to Earth on 16:20 UT 26 January at distance of 0.008 AU (around 3.1 Earth-Moon distances). It is brightest at 04:00 UT on the 27th though. It has an estimated diameter of 680m (a bit over half a kilometer). The asteroid will be a reasonably bright magnitude 9.0 at closest approach, and it comes close to the iconic Beehive cluster when it is still bright.

The flyby of 2004 BL86 will be the closest by any known asteroid of this size until 2027 when asteroid 1999 AN10 goes past Earth. It is also the brightest since 2012 DA14 in 2013.

Unfortunately, from Australia the asteroid is below the horizon at its brightest. We get to see it when it is between magnitudes 10-9.6. The theshold for unaided eye viewing is magnitude 6, so the asteroid is quite dim. Australians can see the asteroid move from Puppis (on the late evening of the 26th, Australia day) through Monocerous and into Hydras.

While the asteroid can be picked up by high end binoculars under dark sky conditions, for most observers small telescopes will be required. My small 114 mm Newtonian with a 25 mm eyepiece allows me to see stars dimmer than magnitude 10.

The printable charts above will also help you find the asteroid. For telescope users, the image will be upside down compared to the charts (so hold the binocular/telescope chart upside down). Remember, when looking for the asteroid allow at least 5 minutes or more (10 is better) for your eyes to adjust and become dark adapted. Here's some hints on dark adaption of your eyes. If using the charts above, cover your torch with red cellophane so as to not destroy your night vision.

When looking for the asteroid in the early morning, we have a good signpost and viewing opportunity. The asteroid comes close to (eastern states) and crosses (western and central states) the relatively bright (magnitude 5.8) open cluster M48 before astronomical twilight. If you find the open cluster then you can camp out on it and watch the asteroid creep towards it.

You can find the cluster fairly easily. If you draw a line between Jupiter and Sirrius (the two brightest objects in the sky at this time), then draw a line perpendicular from procyon (the third brightest object in that part of the sky) to the Jupiter - Sirius line, you should be able to (just see) M48. It will be quite obvious in binoculars or a telescopes finder scope.

With the cluster in view, sweep slowly south around half a field of view at a time. The asteroid may be initially difficult to distinguish as a fairly dim dot, even in a telescope, but it is the only dimmish dot moving slowly and relentlessly towards the cluster.  It may take half an hour to cross the field of view of a wide field eye-piece, but it's motion is fast enough to pick it up.

For central states the asteroid crosses the cluster from around 4:40 to 4:50 am ACDST (3:40-3:50 ACST), for Western Australia the asteroid crosses M48 between roughly 2:10 am - 2:20 am AWST (it is much higher in the sky, so easier to pick up in WA). In the eastern states the asteroid is two cluster widths away from M48 at astronomical twilight (roughly 3:48 am AEST and 4:36 am AEDST).

For those of you familiar with charts and ephemerides, you can generate your own ephemeris using the MPEC ephemeris generator. http://www.minorplanetcenter.net/iau/MPEph/MPEph.html

Use your longitude and latitude for an ephemeris for your location, remember the times are in UT adn it is best to choose and observing interval of around 15 minutes as the asteroid is moving relatively quickly.

Here's some NEO's I've captured in the past.

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Hi Ian,

thanks for the great track-plot of (357439) 2004 BL86.

Can you generate any for my location (Townsville) for this evening?

I would appreciate it as I am struggling to find anything as good as your track plot...


Leigh Franks

Sorry Leigh, I was out Australia Daying and didn't see your post. However my charts will be fine for Townsville, Just use local time (look at 3:30 am instead of 4:50 am)
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