I don’t get to see the parhelic circle very often. It is usually faint—albeit unmistakable—even on the few occasions it appears. The best recent show was over a year ago when the sky displayed not only a parhelic circle, but also a 22° halo, parhelia (sundogs), and (amazingly) a paranthelion.
The parhelic circle is a white line around the sky (or portion of it) at the height of the Sun. It sometimes is seen in cirrus when the ice crystals assume simple shapes (such as hexagonal plates) with vertical sides. Those sides drag a mirror image of the Sun around the sky.
As the circle is at the same angular elevation as the Sun, it is not difficult to find. On a day with cirrus, lift your arm and point at the Sun. Now, holding your arm at that angle, turn slowly so as to draw a line around the sky with your finger. Where the line intersects the cirrus, look to see if there is a parhelic circle.
Dorothy Fraser’s picture of the parhelic circle is used with permission.