Glory (optical phenomenon)

Glories arise due to wave interference of light internally refracted within small droplets.

Appearance and observation

Depending on circumstances (such as the uniformity of droplet size in the clouds), one or more of the glory's rings can be visible. The rings are rarely complete, being interrupted by the shadow of the viewer. The angular size of the inner and brightest ring is much smaller than that of a rainbow, about 5° to 20°, depending on the size of the droplets. In the right conditions, a glory and a rainbow can occur simultaneously.

"Glories can be seen on mountains and hillsides, from aircraft and in sea fog and even indoors."

Like a rainbow, outdoor glories are centred on the antisolar (or, in case of the moon, antilunar) point, which coincides with the shadow of the observer's head. Because this point is diametrically opposite to the sun's (or moon's) position in the sky, it usually lies below the observer's horizon except at sun (or moon) rise and set. Outdoor glories are commonly observed from aircraft. In the latter case, if the plane is flying sufficiently low for its shadow to be visible on the clouds, the glory always surrounds it. This is sometimes called The Glory of the Pilot.

In 2024 astronomers suggested that the existence of glory might explain certain observations of the exoplanet WASP-76b. If this interpretation could be confirmed, it would become the first extrasolar glory-like phenomenon to be discovered.

Brocken spectre

When viewed from a mountain or tall building, glories are often seen in association with a "Brocken spectre": the apparently enormously magnified shadow of an observer, cast (when the sun is low) on clouds below the mountain or tall building on which the viewer is standing. The name derives from the Brocken, the tallest peak of the Harz mountain range in Germany. Because the peak is above the cloud level and the area is frequently misty, conditions conducive to casting a shadow on a cloud layer are common. Giant shadows that seemed to move by themselves due to movement of the cloud layer (this movement is another part of the definition of the Brocken spectre), and that were surrounded by glories, may have contributed to the reputation the Harz mountains hold as a refuge for witches and evil spirits. In Goethe's Faust, the Brocken is called the Blocksberg and is the site of the Witches' Sabbath on Walpurgis Night.

Ulloa's halo

Before the first reports of the phenomenon in Europe, two members of the French Geodesic Mission to the Equator, Antonio de Ulloa and Pierre Bouguer, reported that while walking near the summit of the Pambamarca mountain, in the Ecuadorian Andes, they saw their shadows projected on a lower-lying cloud, with a circular "halo or glory" around the shadow of the observer's head. Ulloa noted that

The most surprising thing was that, of the six or seven people that were present, each one saw the phenomenon only around the shadow of his own head, and saw nothing around other people’s heads.

This was then called "Ulloa's halo" or "Bouguer's halo". Ulloa reported that the glories were surrounded by a larger ring of white light, which would today be called a fog bow. On other occasions, he observed arches of white light formed by reflected moonlight, whose explanation is unknown but which may have been related to ice-crystal halos.