For a low-sun rainbow, its distance to the antisolar point
is about 1[degrees] smaller at its top than at its sides (Fraser 1983; Haufimann 2015).
Depending on whether it is day or night, either the antisolar point
or the Sun respectively will be beneath the horizon; at sunset or sunrise, both will be on the horizon.
By day the center of the rainbow is the antisolar point
, the point exactly opposite the Sun and therefore marked by the shadow of your head.
Your shadow marks the antisolar point
, the direction directly opposite the Sun.
This snapshot of a glory, multicolored rings of light around the antisolar point
(directly opposite the Sun), was captured last October 27th from the summit of Mauna Kea in Hawaii.
Does the Moon ever pass far enough north or south of the antisolar point
to appear out-of-round in binoculars, or even to the naked eye?
From April through early September each year the antisolar point
is too low in the sky for the gegenschein to be seen well from midnorthern latitudes.
So it is the antisolar point
, the point directly opposite the Sun in our sky, at the time of the March equinox (on March 20th this year).
Since a rainbow encircles the antisolar point
(the shadow of your head) at a radius of 42 [degrees], the Moon seen through a rainbow must always be gibbous, three days from full.
It helps if you know to look for the secondary's red band 51 [degrees] from the antisolar point
, the point marked by the shadow of your head.
The antisolar point
directly opposite the Sun is the center that every rainbow arcs around.
As with a rainbow, the shadow of your head marks the antisolar point
and the bow's center.