T
o the unaided eye, Venus is one of
the most beautiful sights in the
sky, outshining every celestial object
except the Sun and the Moon with a
pure white light. However, for telescopic
observers the dazzling face of Venus is
usually a disappointing sight compared
with the richly detailed globes of Mars
and Jupiter. An unbroken canopy of
clouds overlaid by a thick layer of haze
conceals the surface of Venus from pry-
ing eyes. It is not unusual for experi-
enced observers working with powerful
instruments under excellent conditions
to fi nd the planet utterly devoid of
markings of any kind. When markings
are visible, they are almost invariably
diffuse, dusky shadings of low contrast.
It’s a small wonder that three centu-
ries of attempts by visual observers
to discern patterns in the clouds and
determine the planet’s rotation period
all failed miserably.
On rare occasions, however, very
distinct brilliant spots have appearedon Venus. These mysterious, short-lived
features were dubbed “star-spots” by the
British historian of astronomy Richard
Baum (1930–2017), a skilled planetary
observer who directed the Terrestrial
Planets Section of the British Astro-
nomical Association for two decades.
Baum scoured the observational record
and found several credible and intrigu-
ing accounts.
On April 17, 1873, the British
amateur Roger Langdon reported “two
exceedingly bright
spots on the cres-
cent — one close
to the terminator
towards the eastern
horn, and the otherVENUS:^
ESA^ VENUSEXPRES
S;.INSET:^ PAUL^ MAXSON;DRAWING:^ T.^ H
.^ F
OU
LKES,^ COURT
ESY^ OF^ THEB.A.A.52 SEPTEMBER 2019 • SKY & TELESCOPE
in the centre of the crescent. These
spots appeared like two drops of dew...
glistening in such a manner as to cause
the surrounding parts of the bright
crescent to appear dull by contrast.”
February 3, 1884: Belgian astronomer
Charles Émile Stuyvaert saw a very lumi-
nous spot close to the limb of Venus near
the southern cusp of the crescent. He
compared its appearance to one of Jupi-
ter’s Galilean satellites in transit shortly
after entering the disc of the planet.uThe European Space Agency Venus Ex-
press probe recorded a bright feature through
its UV fi lter on July 18, 2009 (main image). The
next day amateur Paul Maxson imaged the
spot with a 10-inch refl ector (inset).uIn February 1897,
Reverend T. H. Foulkes
detected a bright
“hump” (A) and a white
spot (B) while observ-
ing Venus from the
island of Malta.SEPTEMBER 2019 OBSERVING
Exploring the Solar System by Thomas A. DobbinsThe
Mysterious
“Star-Spots”
of Venus
Could these bright patches
be related to volcanism? Spot