In the opposite direction of the sun a bright spot appeared in an unusual bright circle (see Rainbows and Glories). A separation of colours was not recognizable. The event lasted for approximately 30 min. Intensity and clear visibility varied during that time interval. All images were taken with a polarisation filter. Antihelion3.jpg and Antihelion5.jpg show different parts of the horizontal arch where also a small parhelion with colour separation occurred.

It was hard to find similar pictures in the literature. In the book "From the rainbow to polar lights" (K. Schlegel, Spektrum Publishers, 1995) a similar picture can be found. It is described there as follows: "The very rare antihelion belongs to the phenomena of reflection halos. It is embedded in a horizontal circle around the horizon which is located at the level of the sun. […] The antihelion is very likely caused by an angular reflection at a quadruplet crystal. It appears as a swelling of the horizontal circle." Quadruplet crystals look like a cross ("X"). If a light beam hits the top left leg of the "X", it will be reflected at 90 ° and then hits the lower left leg of the X-crystal.

Here a second 90 ° reflection takes place, this time to the left in direction of the incident beam. In the end a reverse or 180 ° reflection of the incident beam occurs.

Therefore the antihelion has to be located directly in opposite direction to the real sun at the sky. This was the case for the image mentioned above. The sun has to be already (or still) low enough otherwise if the sun is raised to high the opposite point is below the horizon. This optical phenomenon is quite rare, because a sufficient concentration of X-like crystals is rarely formed. These quadruplet crystals sediment with perpendicular alignment to the X-plane. Therefore enough "reflection surfaces" are aligned such that plenty of light beams can be reflected. So the intensity of the reflex will be high enough to be well visible. However not all of these "mirrors" are perfectly aligned so that the antihelion might have a larger angular extension than the sun itself. (If all "mirrors" were perfectly parallel, the sun and its picture would have the same angular extension at the sky.)

In the book "Rainbows, Halos and Glories" (R. Greenler, Cambridge, University Press, 1980) the phenomenon is described differently as "Anthelic Arc" (or "Wegener and Hastings Arc"). According to this explanation hexagonal column-like crystals play an essential role in the generation of an antihelion. According to this the phenomenon should occur more often.

Antihelion1.jpg to Antihelion8.jpg: S. Borrmann, Brezzo di Bedero, Lago Maggiore Region, Northern Italy, 22 August 2004, 4:23 p.m. to 4:27 p.m.

Camera Parameters

Olympus E-1 SLR with 14-200 mm objectives. Exposure and selectivity choice (100 ASA) was performed by the program automation. Colour range (sRGB) and resolution (2560 x 1920 Pixel x 24 colours) was the same for all images.