A tesseral harmonic is a spherical harmonicof the form. These harmonics are so named
because the curves on which they vanish are parallels of latitude and meridians, which divide the surface of a sphere into quadrangles
whose angles are right angles (Whittaker and Watson 1990, p. 392).
Resolving
into factors linear in , multiplied by when is odd, then replacing by allows the tesseral harmonics to be expressed as products
of factors linear in ,
,
and
multiplied by one of 1, , , , , , , and (Whittaker and Watson 1990, p. 536).
. These harmonics are so named
because the curves on which they vanish are 
parallels of latitude and 
meridians, which divide the surface of a sphere into quadrangles
whose angles are right angles (Whittaker and Watson 1990, p. 392).
into factors linear in 
, multiplied by 
when 
is odd, then replacing 
by 
allows the tesseral harmonics to be expressed as products
of factors linear in 
,
,
and 
multiplied by one of 1, 
, 
, 
, 
, 
, 
, and 
(Whittaker and Watson 1990, p. 536).
