[BAA-ebulletin 00574] Asteroid 2011 GP59 makes a close approach

[BAA electronic bulletins service]

This object was discovered on the night of April 8/9 by the Observatorio 
Astronomico de Mallorca (OAM) using a 0.45-m f/2.8 reflector at their La 
Sagra facilities (J75) in Andalusia, Spain (see 
http://www.minorplanets.org/OLS/ ).  The observers involved were S. Sanchez, 
J. Nomen, R. Stoss, M. Hurtado, J. A. Jaume and W. K. Y. Yeung.

2011 GP59 is due to make its closest approach to the Earth on April 15 at 
19h UT at 1.39 lunar-distances but will be brightest at an average magnitude 
of 13.2 around 00h UT on the night of April 14/15 when it will be very 
favourably placed in the sky for observers worldwide.  This is the best NEO 
close approach these past few years and is bright enough to be observed 
visually in large (>0.2-m aperture) telescopes when on the night of Thursday 
14th it will appear as a faint slow-moving star.

Observers should be aware however that the object, which is approximately 60 
metres in diameter, appears to be rotating very quickly, once every 7.35 
minutes in fact.  It is also quite oblong in shape such that its rotation 
makes it look distinctly bright then faint every 4 minutes or so. David 
Briggs observing with the Hampshire Astronomy Group's 0.4-m instrument on 
the evening of April 11 commented, "This is probably the fastest rotator 
I've seen so far in that it completely disappears from view every 3 to 4 
images".

Brian Skiff of Lowell Observatory has completed a lightcurve analysis which 
can be found at:
ftp://ftp.lowell.edu/pub/bas/astlc/2011_GP59.png
Close inspection of Brian's results show that the object is almost certainly 
rotating around more than one axis, i.e. it is tumbling.

Weather for UK observers is likely to deteriorate over the coming days and 
so it might be best to observe tonight (Tuesday) around midnight or later 
when clear skies are forecast for much of England.  Unfortunately it will 
only be 16th magnitude at that time and so will be too faint to be picked up 
visually.  Positions can be found using the Minor Planet Center's ephemeris 
service at:
http://minorplanetcenter.net/iau/MPEph/MPEph.html

Clear skies,

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

rmiles at baa.u-net.com