BAA request for info about an unusual flare in Cassiopeia

[Rick]

Quoting from the latest BAA e-mail circular:

The Association has received a report from a Mr C.E.R. Brook of Plymouth of an unusual flare in Cassiopeia.  Mr Brook observed a bright object, several times as bright as the planet Venus, which flared up in the constellation of Cassiopeia in the position of, or near to, the star Alpha Cassiopeiae at 22 hrs 32 mins UT on 26 June 2002.  Mr Brook apparently had the object in view for about a minute, before it faded rapidly from view, and it showed no sign of movement while visible. It was already bright when Mr Brook first spotted the object.

[Mike]

Hmmm.. Interesting. Sounds like a possible naked eye nova or super.

[Whitters]

Anyone able to check Geo-stationary satellites, It may be just in the right position to generate a flare.

[Rick]

I'd expect Cass is a bit far off the equatorial plane for a geostationary satellite, but it could have been a flare from one of those satellites in a long elliptical orbit like the one Chandra is in....

That said, I'd have expected the BAA to have investigated that possibility before putting out its alert...

[Whitters]

The BAA have an answer

FLARE IN CASSIOPEIA IDENTIFIED

Further to the report in BAA electronic circular No. 00052, from Mr Clive
Brook in Plymouth, of a bright object, several times as bright as the planet
Venus, which flared up in the constellation of Cassiopeia, close to the star
Alpha Cassiopeiae, this was almost certainly an Iridium flare.

Firm identification was initially complicated by the fact that the time and
date of the observation were given as 22:32 UT on 2002 June 26.  In fact,
although the original report was submitted shortly after midnight on June
26, it refers to an event which took place at 22:32 UT on June 25.

A clever piece of detective work by Russell Eberst identified this error,
and
he showed that the flare was caused by the satellite Iridium 61.  It flared
to
mag. -6.3 (about 8 times brighter than Venus) at 22:31:43 UT on 2002 June
25.  The mid-point of the flare was at RA/Dec. 01h 10m, +56, only a few
degrees to the south-east of Alpha Cassiopeiae.

Iridium satellites are slow-moving, hence the notion reported in BAA
e-circular No. 00052 that the flare was stationary. Another eyewitness in
the Plymouth area confirmed that the object was moving slowly.

Calculations by Russell Eberst show that in the 16 seconds centred on the
flare, the satellite moved from 01h 22m, +56 to 00h 57m, +56, passing very
close to Alpha Cassiopeiae at this time.

Further calculations by Nick James using the IRIDFLAR program by Rob Matson
show that the magnitude of Iridium 61 was greater than mag. 2 for about 35
seconds at the time of the Plymouth sighting.

NOTE:

The Iridium satellites are a 'constellation' of fairly small
telecommunications satellites, in six orbital planes, circling the Earth at
an altitude of around 780 km. Each satellite has three main antennas, which
are flat, highly reflective surfaces, that can reflect the Sun's rays to an
observer on the ground when the geometry is just right. Given a knowledge of
the attitude (orientation) of the satellite antennas, together with the
orbital position of the satellite relative to the Sun and to the position of
an observer on the ground, it is possible to calculate the angle between the
direction from the satellite to the observer and the line of a perfect
reflection of the Sun. This so-called 'mirror angle' determines the
magnitude of the flare.

ACKNOWLEDGEMENTS:

The undersigned would particularly like to thank Clive Brook for reporting
his observation of the flare, and Russell Eberst and Nick James for help
with the positive identification of the event.  Thanks are also due to the
very large number of people who contributed to the discussion of this
sighting, and who made many helpful comments and suggestions, together with
those who were prompted to report other sightings made at various times.

Dr John Mason, British Astronomical Association,