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NEWS
February
``black drop'' phenomenon
observed during planetary tran­
couldhave thesameexplana­
similar effect
Saturn, say MEBailey, DStewart
andMStronge. Recent transits Mercury Nov­
ember 1999) Venus
(8 June 2004)
to new interest origin
explanation
of famous ``black
drop'' phenomenon (e.g. Schaefer
2001, Schneider, Pasachoff and
Golub 2004, Sheehan Westfall
2004, references therein).
appears effect
is
optical phenomenon produced
convolution instrumental
point­spread function, including
``seeing'', edge
a planetary
a sharply cut­
limb­darkened background
source illumination. There may
minor contribution
diffraction
of around
edge occulting
Observations
of phenomenon
Green and
1)
are difficult obtain under
controlled conditions owing
infrequency planetary transits
front relatively
short duration. Here, atten­
tion
a similar drop
Saturn.
principle, shadow
planet falls either
ring system
or
on
the Cassini division
eight times every Saturnian orbital
period.
in
groups
of four around
times widest opening.
from Earth, optical circumstances
sharp, dark shadow lying almost
tangent
a sharply cut­off back­
ground source) essentially
same those
in classical black
drop. Recent high­quality amateur
images Saturn show
black extension
in both cases
(figures
In fact, drawings photo­
graphs Saturn show phenom­
enon, which black
often attributed atmospheric
seeing
to some
of optical illu­
anomaly. Alexander (1962)
provides many illustrations
of
effect, earliest example being
drawing William Herschel
1780. Similarly, (1886) shows
effect
in
his
I (drawn
in
summer Trouvelot), not­
(p282--283) planet's
black shadow presents
a number
anomalous features that some
extent
be optical illusion.
Flammarion (1900) that
observations display interest­
`black drop' appearance...''.
We propose that cause
of
effect
in Saturn
is same
as
classical drop case
transit
of Venus. Furthermore,
because viewing geometry varies
much slowly
in
Saturn, future observational studies
of ``Saturnian black drop''
additional insight wider
drop phenomenon.
M Armagh Observatory;
art, Astronomical Association;
M
Stronge, Antrim Astronomical Society.
authors
A Christou,
K
McConnell TMoseley
ful comments suggestions. This
supported
by
the Northern Ireland
Department
of Culture, Arts Leisure.
References Alexander AFO'D ThePlanet Saturn:
AHistory
of Observation, Theoryand Discov­
ery (Faber andFaber, London).
RS1886TheStory Heavens
(Cassell &Co.,London).
FlammarionC1900MNRAS60441--442 andplate GreenCandCookJ 1771 Philosophical
Transactions Society 61397--421.
SchaeferBE2001
J
32
325--336. SheehanWandWestfallJ2004TheTransits
of Venus (Prometheus,Amherst,NewYork).
SchneiderG,PasachoffJMandGolubL 249--256.
Extending the black drop to Saturn
Images transit Venus
1769 byCharlesGreenand James
Cook, showing classical ``black
drop'' phenomenon (RASarchive).
2: ImageofSaturnbyDavid Stewart January2004)
showing black planet's shadow
touches edgeof system.
3: ImageofSaturn MarkandNigelStronge
December2002) showing black effect
planet's shadow just touches Cassini division.
Ball notes the planet's
shadow presents anomalous
features may
optical illusion
Human space­
flight review
convening
a commis­
report case
space, reports SueBowler.
Following decision
provide seedcorn money
Aurora project, RAS formed
a commission
to evidence
the scientific
for humans
in
the astronomical
geophysics perspective. Frank
chair commission,
will produce report
before decision
ticipation Aurora.
Aftab Khan,
on behalf the
British Geophysical Association,
wants feedback forthcom­
Review
of Geophysics Educa­
wants
it
discussionmeeting April.
promoting
awareness geophysics
in schools
colleges, teaching, learn­
career development geo­
physicsts, Geophysical
Association association
of
Geological Society
London)
is carrying
a Review
Geophysics Education and
plans
to report summer
2005. Notices Review
already appeared October
issues A&G Geoscientist.
wide
of issues
covered need
widest possible consultation,
Association hosting
an
meeting Geological Society
from
2 Friday
discuss preliminary findings
and recommendations Review.
Review guide future
on geophysics education
UK, Association invites anyone
with interest
in subject
attend.
It particularly important
representation students universities
undergraduate post­
graduate courses; school science
teachers; employers from
mining, engineering, water other
industries; commerce; relevant
research establishments; pub­
sector. 3.30--4 p.m.
discussion will
be followed
reception would
helpful attendees inform
Education Secretary, Chris­
Thomas, University Liverpool,
tine@liverpool.ac.uk advance.
BGA seeks help plan geophysics education