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Thursday, 22 January 2015

[BAA-ebulletin 00836] 2004 BL86 - An unusually bright close-approaching asteroid

BAA electronic bulletin
On the night of January 26/27, asteroid 2004 BL86 will make a close
pass of the Earth becoming, for a short time, the brightest natural
near-Earth object (NEO) that we know of (other than the Moon) over the
next 12 years. The object will be very favourably placed for
observation, especially for observers based in the UK and Europe.

This potentially hazardous asteroid (PHA) is quite large, some 0.4-1.0
km across, and so will appear as bright as 9th magnitude when it
passes the Earth at the safe distance of 1.2 million kilometres.
Although it orbits the Sun every 1.84 years ranging between 0.90 AU
and 2.11 AU, the forthcoming event marks its closest geocentric
approach for several centuries when it will pass almost 3
lunar-distances away on January 26 at 16:20 UT. This close approach is
especially unusual (for a PHA) in that it will continue to brighten by
more than a factor of 2 after closest approach whilst it moves towards
opposition, reaching the remarkably low phase angle of 1.1 degrees,
and attaining a V magnitude of 9.0 on Tuesday, January 27 between
03:40-05:10 UT, during which time interval its apparent speed will
have slowed to ~2"/sec.

Please note that its visibility as seen from Europe and North America
is very favourable, and so you will not have to wait up until the
early hours to spot it since (seen from the UK) the 9th magnitude
object will rise and become readily visible soon after 19:00 UT. Its
motion should be very obvious as seen through a small telescope (10-cm
aperture or larger instrument) when it heads northwards leaving the
constellation of Hydra and entering Cancer at around 23:10 UT on the

Charts showing the object's track across the sky for the night of
January 26/27 (for UK-based observers) have been prepared by Steve
Harvey, Director of our Computing Section.
For Jan 26.5-27.0, the chart is at:
Likewise for Jan 27.0-27.5, Steve's chart is here:

At its brightest, large binoculars should reveal the interloper as it
slowly migrates across the field of view. Between 05:05-05:45 UT on
the 27th, the asteroid glides past the western (following) edge of the
Beehive star cluster (Messier 44) as seen from southern England.
Parallax will significantly affect its apparent position as seen by
observers elsewhere. So if you wish to obtain exact celestial
coordinates for your location, these can be downloaded from the Minor
Planet & Comet Ephemeris Service:
You will need to enter your latitude and longitude (or observatory
code - in uppercase - at or near your location) using the online form
together with the time (in UT) when you are planning to observe. Using
large telescopes with small fields of view, you might consider
pointing the scope at a point in the sky where the asteroid is due to
pass say 5 or 10 minutes later. You will hen be able to monitor the
object coming into view and traversing your field before disappearing
at the opposite edge of the frame.

Updates as to the nature of this object and links to charts, together
with observations by members, will be posted on the Asteroids and
Remote Planets Section homepage:
Watch out for brightness fluctuations as it spins on its axis: that's
if 2004 BL86 turns out to be rather elongated in shape, or indeed if
it happens to be a binary system. It is also worth observing with
different filters to see whether its colour changes as it spins, or
even spectroscopically to classify its type. Astrometry made from
observatories assigned an IAU code should be reported to the Minor
Planet Center in the usual way. Images and photometry will be collated
by myself as section director - arps [at]

Good luck to all weather-wise.

Richard Miles
Director, Asteroids and Remote Planets Section
British Astronomical Association

2015 January 22
BAA-ebulletin mailing list visit:
(c) 2014 British Astronomical Association

Good Clear Skies
Colin James Watling
Various Voluntary work-Litter Picking for Parish Council (Daytime) and
also a friend of Kessingland Beach (Watchman)
Real Astronomer and head of the Comet section for LYRA (Lowestoft and
Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland
Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
Lyra Main Website:

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