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Wednesday, 2 November 2011

Fwd: [BAA-ebulletin 00625] Close-approach of asteroid 2005 YU55

BAA electronic bulletin
This is an announcements only list - please do not reply to the list address.
Seen from the UK on the evening of Tuesday, November 8/9, a 400-metre size
asteroid 2005 YU55 will pass within 0.85 lunar-distances of us travelling at
a speed of 13.7 km/s relative to the Earth.  This encounter will be the
closest known for an asteroid of this size between the years, 1976 and 2028.
So in this respect, it is a once in a 52-year opportunity to witness this
particular skirmish.

It should first become visible from the UK and Europe on Tuesday evening,
low in the west mainly in Aquila, passing 22 degrees south-west of Comet
Garradd (C/2009 P1).  It should prove fascinating to follow as it
approaches.  Seen from southern England (Dorset), it may be first detectable
using a CCD camera and large telescope at about 18:00UT some 23 degrees
altitude in the south-west direction at about magnitude 15 moving at 5
"/sec. It will brighten by about a factor of 10 over the next 4 hours so
that by 22:00UT it will be 12th magnitude and moving at around 8 "/sec, i.e.
crossing the sky at a rate of 1 Moon-diameter every 3.6 minutes.  Even
exposures of a few seconds will show the asteroid as a trail and only
telescope mounts set up to track moving objects will be able to register it
as a point source. It will attain 11th magnitude at closest approach (Nov 8
at 23:28UT) at an altitude of just 6 degrees (as seen from Dorset) and
thereafter will set below the western horizon.  With a very high apparent
speed (reaching almost 9 "/sec), the object will be visible through large
telescopes (25cm or greater) looking like a moving point of light crossing
the field of view in a minute or two. Quite an observing challenge!

2005 YU55 will be much better placed for observers and easier to see on the
evening of November 9/10 when at about 18:00UT it will be 12th magnitude and
moving at <1 "/sec in the east close (12 degrees away) to the nearly full
Moon.  Martin Mobberley has kindly generated a finder chart showing the
general position of the asteroid for the nights of Nov 9/10, 10/11 and
11/12.  The chart can be found at:

If you are planning to observe then you will need to generate an ephemeris
for a geographical location within a few hundred kilometres of your
observing site.  You may find the Minor Planet Center website convenient to
use for this purpose, located at:
Be sure to enter an observatory code in the relevant box: "J95" would be a
good one to use by anyone in southern England. You will have to pick a short
'ephemeris interval' say 5 minutes so that you can point your telescope at a
convenient spot which the asteroid will reach some minutes after the
telescope has been trained on a suitable R..A. and Dec. Enter "2005 YU55" in
the large box and an ephemeris start date using the following format, "2011
11 09 1800".

The object was last observed in 2010 April when the Arecibo radio telescope
was used to generate a radar image of the near-spherical object, and which
was shown to be very dark and a slow rotator turning just once every 18
hours or so.  See for example:

Although a potentially hazardous object, we do know that this is the closest
approach the object will make to the Earth during the next 100 years.

All observations welcome. Good luck with the weather,

Richard Miles
Director, Asteroids and Remote Planets Section

(This bulletin has also been bcc'd to section members - apologies if you
receive 2 copies)
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(c) 2011 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)
Information -- More Info -- And More Info

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