Venus
(planet)
Venus
is
the
second
planet
from
the
Sun,
named
after
the
Roman
goddess
Venus.
It
is
a
terrestrial
planet,
very
similar
in
size
and
bulk
composition
to
Earth;
it
is
sometimes
called
Earth's
"sister
planet"
as
a
result
of
this
similarity.
Sometimes
(inaccurately)
referred
to
as
the
"morning
star"
or
the
"evening
star",
it
is
by
far
the
brightest
"star"
in
the
sky.
Because
Venus
is
closer
to
the
Sun
than
Earth
is,
it
is
always
in
roughly
the
same
direction
as
the
Sun,
so
can
only
be
seen
just
before
sunrise
or
just
after
sunset.
Physical
characteristics
Atmosphere
Venus
has
an
atmosphere
consisting
mainly
of
carbon
dioxide
and
a
small
amount
of
nitrogen,
with
a
pressure
at
the
surface
about
90
times
that
of
Earth
(a
pressure
equivalent
to
a
depth
of
1
kilometer
under
Earth's
ocean).
This
enormous
CO2-rich
atmosphere
results
in
a
strong
greenhouse
effect
that
raises
the
surface
temperature
approximately
400°C
above
what
it
would
be
otherwise,
causing
temperatures
at
the
surface
to
reach
500°C.
This
makes
Venus's
surface
hotter
than
Mercury's,
despite
being
nearly
twice
as
distant
from
the
Sun
and
only
receiving
75%
the
solar
irradiance
(2660
W/m2).
Due
to
the
thermal
inertia
and
convection
of
its
dense
atmosphere,
the
temperature
does
not
vary
significantly
between
the
night
and
day
sides
of
Venus
despite
its
extremely
slow
rotation
(less
than
one
rotation
per
Venusian
year).
Winds
in
the
upper
atmosphere
circle
the
planet
in
only
4
days,
helping
to
distribute
the
heat.
There
are
strong
350-kilometer-per-hour
winds
at
the
cloud
tops
but
winds
at
the
surface
are
very
slow,
no
more
than
a
few
kilometers
per
hour.
However,
due
to
the
high
density
of
the
atmosphere
at
Venus's
surface,
even
such
slow
winds
exert
a
significant
amount
of
force
against
obstructions.
The
clouds
are
composed
of
sulfur
dioxide
and
sulphuric
acid
droplets
and
cover
the
planet
completely,
obscuring
any
surface
details.
The
temperature
at
the
tops
of
these
clouds
is
approximately
-45°C.
The
official
mean
surface
temperature
of
Venus,
as
given
by
NASA,
is
464°C.
The
minimal
value
of
the
temperature,
listed
in
the
table,
refers
to
cloud
tops
-
on
surface
the
temperature
is
never
below
400°C.
Surface
features
Venus
has
slow
retrograde
rotation,
meaning
it
rotates
from
east
to
west
instead
of
west
to
east
as
all
other
known
planets
in
the
solar
system
do.
It
is
not
known
for
sure
why
Venus
is
different
in
this
manner,
although
it
may
be
the
result
of
a
collision
with
a
very
large
asteroid
at
some
time
in
the
distant
past.
In
addition
to
this
unusual
retrograde
rotation,
the
periods
of
Venus's
rotation
and
of
its
orbit
are
synchronized
in
such
a
way
that
it
always
presents
the
same
face
toward
Earth
when
the
two
planets
are
at
their
closest
approach
(5.001
Venusian
days
between
each
inferior
conjunction).
This
may
be
the
result
of
tidal
locking,
with
tidal
forces
affecting
Venus's
rotation
whenever
the
planets
get
close
enough
together,
or
it
may
simply
be
a
coincidence.
Venus
has
two
major
continent-like
highlands
on
its
surface,
rising
over
vast
plains.
The
northern
highland
is
named
Ishtar
Terra
and
has
Venus's
highest
mountains,
named
the
Maxwell
Montes
after
James
Clerk
Maxwell,
which
surround
the
plateau
Lakshmi
Planum.
Ishtar
Terra
is
about
the
size
of
Australia.
In
the
southern
hemisphere
is
the
larger
Aphrodite
Terra,
about
the
size
of
South
America.
Between
these
highlands
are
a
number
of
broad
depressions,
including
Atalanta
Planitia,
Guinevere
Planitia,
and
Lavinia
Planitia.
With
only
the
exception
of
Maxwell
Montes,
all
surface
features
on
Venus
are
named
after
real
or
mythological
females.
Due
to
Venus's
thick
atmosphere,
which
causes
meteors
to
decelerate
as
they
fall
toward
the
surface,
no
impact
crater
smaller
than
about
3.2
km
in
diameter
can
form.
Nearly
90%
of
Venus's
surface
appears
to
consist
of
recently-solidified
basalt
lava,
with
very
few
meteor
craters.
This
suggests
that
Venus
underwent
a
major
resurfacing
event
recently.
The
interior
of
Venus
is
probably
very
similar
to
that
of
Earth:
an
iron
core
about
3000
km
in
radius,
with
a
molten
rocky
mantle
making
up
the
majority
of
the
planet.
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