Definition of Parallax
Par´al`lax
n.
1.
The
apparent
displacement
,
or
difference
of
position
,
of
an
object
,
as
seen
from
two
different
stations
,
or
points
of
view
.
2.
(Astron.)
The
apparent
difference
in
position
of
a
body
(
as
the
sun
,
or
a
star
)
as
seen
from
some
point
on
the
earth
'
s
surface
,
and
as
seen
from
some
other
conventional
point
,
as
the
earth
'
s
center
or
the
sun
.
3.
(Astron.)
The
annual
parallax
.
See
annual
parallax
,
below
.
Annual parallax
the
greatest
value
of
the
heliocentric
parallax
,
or
the
greatest
annual
apparent
change
of
place
of
a
body
as
seen
from
the
earth
and
sun
;
it
is
equivalent
to
the
parallax
of
an
astronomical
object
which
would
be
observed
by
taking
observations
of
the
object
at
two
different
points
one
astronomical
unit
(
the
distance
of
the
Earth
from
the
sun
)
apart
,
if
the
line
joining
the
two
observing
points
is
perpendicular
to
the
direction
to
the
observed
object
;
as
,
the
annual parallax
of
a
fixed
star
.
The
distance
of
an
astronomical
object
from
the
Earth
is
inversely
proportional
to
the
annual parallax
.
A
star
which
has
an
annual
parallax
of
one
second
of
an
arc
is
considered
to
be
one
parsec
(
3
.
26
light
years
)
distant
from
the
earth
;
a
star
with
an
annual
parallax
of
one-hundredth
second
of
an
arc
is
326
light
years
distant
.
See
parsec
in
the
vocabulary
,
and
stellar
parallax
,
below
.
Binocular parallax
the
apparent
difference
in
position
of
an
object
as
seen
separately
by
one
eye
,
and
then
by
the
other
,
the
head
remaining
unmoved
.
Diurnal parallax
the
parallax
of
a
body
with
reference
to
the
earth
'
s
center
.
This
is
the
kind
of
parallax
that
is
generally
understood
when
the
term
is
used
without
qualification
.
Heliocentric parallax
the
parallax
of
a
body
with
reference
to
the
sun
,
or
the
angle
subtended
at
the
body
by
lines
drawn
from
it
to
the
earth
and
sun
;
as
,
the
heliocentric parallax
of
a
planet
.
Horizontal parallax
the
geocentric
parallx
of
a
heavenly
body
when
in
the
horizon
,
or
the
angle
subtended
at
the
body
by
the
earth
'
s
radius
.
Optical parallax
the
apparent
displacement
in
position
undergone
by
an
object
when
viewed
by
either
eye
singly
.
Parallax of the cross wires
of
an
optical
instrument
),
their
apparent
displacement
when
the
eye
changes
its
position
,
caused
by
their
not
being
exactly
in
the
focus
of
the
object
glass
.
- Brande & C.
Stellar parallax
the
annual
parallax
of
a
fixed
star
.
Related Words
annual
parallax
,
diurnal
parallax
,
geocentric
parallax
,
heliocentric
parallax
,
optical
phenomenon
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