the
term
planet
is
ancient
with
ties
to
history
astrology
science
mythology
and
religion
several
planets
in
the
solar
system
can
be
seen
with
the
naked
eye
these
were
regarded
by
many
early
cultures
as
divine
or
as
emissaries
of
deities
as
scientific
knowledge
advanced
human
perception
of
the
planets
changed
incorporating
a
number
of
disparate
objects
in
2006
the
international
astronomical
union
iau
officially
adopted
a
resolution
defining
planets
within
the
solar
system
this
definition
is
controversial
because
it
excludes
many
objects
of
planetary
mass
based
on
where
or
what
they
orbit

although
eight
of
the
planetary
bodies
discovered
before
1950
remain
"planets"
under
the
modern
definition
some
celestial
bodies
such
as
ceres
pallas
juno
and
vesta
each
an
object
in
the
solar
asteroid
belt
and
pluto
the
first
trans-neptunian
object
discovered
that
were
once
considered
planets
by
the
scientific
community
are
no
longer
viewed
as
such

the
planets
were
thought
by
ptolemy
to
orbit
earth
in
deferent
and
epicycle
motions
although
the
idea
that
the
planets
orbited
the
sun
had
been
suggested
many
times
it
was
not
until
the
17th
century
that
this
view
was
supported
by
evidence
from
the
first
telescopic
astronomical
observations
performed
by
galileo
galilei

at
about
the
same
time
by
careful
analysis
of
pre-telescopic
observation
data
collected
by
tycho
brahe
johannes
kepler
found
the
planets'
orbits
were
not
circular
but
elliptical
as
observational
tools
improved
astronomers
saw
that
like
earth
the
planets
rotated
around
tilted
axes
and
some
shared
such
features
as
ice
caps
and
seasons
since
the
dawn
of
the
space
age
close
observation
by
space
probes
has
found
that
earth
and
the
other
planets
share
characteristics
such
as
volcanism
hurricanes
tectonics
and
even
hydrology

planets
are
generally
divided
into
two
main
types
large
low-density
giant
planets
and
smaller
rocky
terrestrials
under
iau
definitions
there
are
eight
planets
in
the
solar
system
in
order
of
increasing
distance
from
the
sun
they
are
the
four
terrestrials
mercury
venus
earth
and
mars
then
the
four
giant
planets
jupiter
saturn
uranus
and
neptune
six
of
the
planets
are
orbited
by
one
or
more
natural
satellites
