Lomography

To you, the bird

Because refraction generally raises the apparent position of objects above their geometric positions,it compresses more than a hemisphere of the real sky into the hemisphere above the astronomical horizon.So the effectof standard refraction is to compress objects seen near the horizon. However, mirages involve rapid changes in refraction with apparent altitude.Some zones of the sky are compressed more than npormal;others are compressed less, or even expanded.This effect is particularly important in the inferior mirage, for it's what makes inferior-mirage flashes thick enough to see with thye naked eye.Unfortunately, the expanded zone is usually only a couple of minutes of arc wide - near the limit of resolution of the unaided eye.But even one minute of arc is about four times the normal width of the the green rim, so it represents an important magnification of this feature, which is the source of the inferior-mirage flash.When seen through a magnifying mirage, the green rim can become big enough to see easily.