A Bottlinger's Ring is a type of halo that is elliptical, instead of circular as the 22° halo or the 46° halo. Because it is so small however, it is usually seen around the Subsun. Sometimes they occur around the Sun, but the Sun makes it very hard to see. Because of this, they are only seen on airplanes. Bottlinger's rings are not well understood yet.
Formation
The Bottlinger's ring is formed by pyramidial crystals. Because of the unique shape of the crystal, it cause it to be elliptical. It is suggested that the crystals have faces angled at low angles. They are also suggested to be very flat, but more research needs to be done for the exact process. The halo is also much more uncommon than ones above the horizon because it requires precisely orientated crystals.