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THE ASTRONOMER Electronic Circular No 2983      2014 Feb 25 16.15UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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GAIA
Priv.-Doz. Dr. Stefan Jordan, Heidelberg, Germany has contacted Nick James
to relay the following messages to TA observers regarding the brightness of
Gaia.

Tomorrow, 2014 February 26, at 11:58 UTC, Gaia will change its aspect angle
with respect to the Sun from 42 degrees to zero degrees. This manoeuvre will
take eight minutes. The exact times are:
Slew  SAA42 -> SAA0
starts: UTC  2014/02/26 11:58:52.815
ends:   UTC  2014/02/26 12:06:43.815

We expect that Gaia will be considerably brighter than the current 20-20.5
mag after the move to zero degrees until it will again change its solar
aspect angle to 45 degrees on Feb 27, 09:06 UTC. It is possible that Gaia
will brighten by about 5 magnitudes.

Slew SAA0 -> SAA45
starts: UTC  2014/02/27 09:06:43.478
ends:   UTC  2014/02/27 09:15:11.978

The most interesting phase to take pictures and measure the brightness is
the time of the manoeuvre itself because you could see the brightness
varying on a time scale of minutes. For us data from this time period would
be particularly useful because photometric measurements could tell us how
Gaia’s sunshield reflects sunlight in different directions.

The time of the manoeuvre excludes observers from Europe, because the change
of the aspect angle takes place during daylight at our longitudes.
Nevertheless, observations from the night between Feb 26 and Feb 27 would
also be very interesting.

Gaia’s ephemerides can be obtained at http://gaiainthesky.obspm.fr/fov/ 

This information comes at very short notice but the exact times of the
manoeuvre were not available earlier.

Please send observations to Martin Altmann (maltmann@ari.uni-heidelberg.de)
and me (jordan@ari.uni-heidelberg.de). For TA observers could we also ask
for a copy to be sent to Dr. Mark Kidger, sub-editor of TA Planetary Notes
(mrkidger@hotmail.com)

Guy M Hurst