<s>
Optical	B-Algorithm
depth	I-Algorithm
in	O
astrophysics	O
refers	O
to	O
a	O
specific	O
level	O
of	O
transparency	O
.	O
</s>
<s>
Optical	B-Algorithm
depth	I-Algorithm
and	O
actual	O
depth	O
,	O
and	O
respectively	O
,	O
can	O
vary	O
widely	O
depending	O
on	O
the	O
absorptivity	O
of	O
the	O
astrophysical	O
environment	O
.	O
</s>
<s>
Optical	B-Algorithm
depth	I-Algorithm
is	O
a	O
measure	O
of	O
the	O
extinction	O
coefficient	O
or	O
absorptivity	O
up	O
to	O
a	O
specific	O
'	O
depth	O
 '	O
of	O
a	O
star	O
's	O
makeup	O
.	O
</s>
<s>
From	O
the	O
definition	O
,	O
it	O
is	O
also	O
clear	O
that	O
large	O
optical	B-Algorithm
depths	I-Algorithm
correspond	O
to	O
higher	O
rate	O
of	O
obscuration	O
.	O
</s>
<s>
Optical	B-Algorithm
depth	I-Algorithm
can	O
therefore	O
be	O
thought	O
of	O
as	O
the	O
opacity	O
of	O
a	O
medium	O
.	O
</s>
<s>
where	O
is	O
the	O
effective	O
temperature	O
at	O
that	O
depth	O
and	O
is	O
the	O
optical	B-Algorithm
depth	I-Algorithm
.	O
</s>
<s>
This	O
illustrates	O
not	O
only	O
that	O
the	O
observable	O
temperature	O
and	O
actual	O
temperature	O
at	O
a	O
certain	O
physical	O
depth	O
of	O
a	O
star	O
vary	O
,	O
but	O
that	O
the	O
optical	B-Algorithm
depth	I-Algorithm
plays	O
a	O
crucial	O
role	O
in	O
understanding	O
the	O
stellar	O
structure	O
.	O
</s>
