the
au
was
originally
defined
as
the
length
of
the
semi
major
axis
of
the
earth
s
elliptical
orbit
around
the
sun
in
the
international
astronomical
union
revised
the
definition
of
the
au
for
greater
precision
defining
it
as
that
length
for
which
the
gaussian
gravitational
constant
k
takes
the
value
when
the
units
of
measurement
are
the
astronomical
units
of
length
mass
and
time
an
equivalent
definition
is
the
radius
of
an
unperturbed
circular
newtonian
orbit
about
the
sun
of
a
particle
having
infinitesimal
mass
moving
with
an
angular
frequency
of
radians
per
day
or
that
length
for
which
the
heliocentric
gravitational
constant
the
product
gm
is
equal
to
au
d
it
is
approximately
equal
to
the
mean
earth
sun
distance

the
au
was
originally
defined
as
the
length
of
the
semi
major
axis
of
the
earth
s
elliptical
orbit
around
the
sun
in
the
international
astronomical
union
revised
the
definition
of
the
au
for
greater
precision
defining
it
as
that
length
for
which
the
gaussian
gravitational
constant
k
takes
the
value
when
the
units
of
measurement
are
the
astronomical
units
of
length
mass
and
time
an
equivalent
definition
is
the
radius
of
an
unperturbed
circular
newtonian
orbit
about
the
sun
of
a
particle
having
infinitesimal
mass
moving
with
an
angular
frequency
of
radians
per
day
or
that
length
for
which
the
heliocentric
gravitational
constant
the
product
gm
is
equal
to
au
d
it
is
approximately
equal
to
the
mean
earth
sun
distance