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Light pillar
View on Wikipediafrom Wikipedia
A light pillar or ice pillar is an atmospheric optical phenomenon in which a vertical beam of light appears to extend above and/or below a light source. The effect is created by the reflection of light from tiny ice crystals that are suspended in the atmosphere or that compose high-altitude clouds (e.g. cirrostratus or cirrus clouds).[1] If the light comes from the Sun (usually when it is near or even below the horizon), the phenomenon is called a sun pillar or solar pillar. Light pillars can also be caused by the Moon or terrestrial sources, such as streetlights and erupting volcanoes.[2]
Formation
[edit]
Since they are caused by the interaction of light with ice crystals, light pillars belong to the family of halos. The crystals responsible for light pillars usually consist of flat, hexagonal plates, which tend to orient themselves more or less horizontally as they fall through the air. Each flake acts as a tiny mirror which reflects light sources that are appropriately positioned below it (see drawing), and the presence of flakes at a spread of altitudes causes the reflection to be elongated vertically into a column. The larger and more numerous the crystals, the more pronounced this effect becomes. More rarely, column-shaped crystals can cause light pillars as well.[3] In very cold weather, the ice crystals can be suspended near the ground, in which case they are referred to as diamond dust.[4]
Unlike a light beam, a light pillar is not physically located above or below the light source. Its appearance as a vertical line is an optical illusion, resulting from the collective reflection off the ice crystals; but only those that are in the common vertical plane, direct the light rays towards the observer (See drawing). This is similar to viewing a light source on a body of water. Ripples on the surface of the water reflect the light source in many directions, and those that happen to be aimed at the viewer, combine to form a bright line pointing toward the light source.[5]
See also
[edit]References
[edit]- ^ "Colonne lumineuse". World Meteorological Organization. Archived from the original on 23 September 2016.
- ^ "Light Pillar over Volcanic Etna". apod.nasa.gov. NASA. 15 November 2021. Retrieved 2 June 2024.
- ^ "Sun pillars from column crystals". www.atoptics.org.uk. Retrieved 29 September 2025.
- ^ "APOD: 2013 December 18 – Light Pillars over Finland". apod.nasa.gov.
- ^ "Light Pillars". www.atoptics.org.uk. Retrieved 29 September 2025.
External links
[edit]
Wikimedia Commons has media related to Sun pillar.
- Pillars. Atmospheric Optics. Explanations (10 pages) and many images.
- Light Pillars: An Introduction to Sun Pillars and Related Phenomena. The Weather Doctor's Weather Eyes. Another nice explanation, all on one page
- Fabulous frozen frames – Sydney Morning Herald. November 1, 2006
- A Sun Pillar Over North Carolina. NASA Astronomy Picture of the Day, 15 December 2008
Light pillar
View on Grokipediafrom Grokipedia
A light pillar, also known as a sun pillar or ice pillar, is an atmospheric optical phenomenon characterized by a vertical beam of light that appears to extend above and/or below a light source, such as the sun, moon, or artificial lights like streetlamps.[1][2] This striking effect occurs when light reflects off the flat, horizontal surfaces of numerous plate-shaped or pencil-shaped ice crystals suspended in the air, creating the illusion of a pillar without actual emission of light from the crystals themselves.[1][3]
The formation of light pillars relies on specific atmospheric conditions, typically involving cold temperatures below freezing where high-altitude cirrus or cirrostratus clouds contain hexagonal ice crystals that fall slowly with their broad faces oriented nearly horizontal.[2][1] As these crystals gently rock or wobble while descending, they act like tiny mirrors, reflecting light rays in a direction parallel to the ground, which concentrates the reflections into a bright vertical column aligned with the light source.[3][1] Unlike refractive phenomena such as halos or sundogs, light pillars result purely from reflection, producing a colorless beam rather than a spectrum of colors.[2]
Light pillars are most commonly observed during twilight hours at sunrise or sunset when the sun is low on the horizon (below about 10 degrees elevation), enhancing the visibility of the column extending upward or downward for several degrees.[2][1] They can also form around the moon under similar icy conditions or from terrestrial lights in urban areas during very cold, clear nights with diamond dust—fine ice crystals near the ground.[3] Notable examples include widespread sightings in polar regions like Alaska during winter, where prolonged cold fosters abundant ice crystals, and occasional appearances in mid-latitudes during outbreaks of arctic air.[3] These pillars, while beautiful and ephemeral, pose no threat and serve as indicators of upper-atmospheric ice presence.[2]
Overview
Definition
A light pillar is an atmospheric optical phenomenon characterized by a vertical beam of light that appears to extend above and/or below a light source, resulting from the reflection of sunlight, moonlight, or artificial light off tiny ice crystals suspended in the atmosphere.[2][4] This effect belongs to the family of halos and is caused by the interaction of light with flat, plate-like ice crystals that orient horizontally as they fall through the air.[5] The pillar manifests as a luminous column aligned vertically with the light source, creating an illusion of a shaft projecting upward or downward, which can span several degrees in height depending on the distribution of ice crystals.[6] It is frequently misidentified by observers as a searchlight beam or unidentified flying object due to its striking, artificial-like appearance against the sky.[4] Historically, the phenomenon has been referred to as a light shaft or solar pillar, particularly when involving sunlight near the horizon.[4]Visual characteristics
Light pillars manifest as smooth, vertical columns of light that appear to extend upward from a light source, creating the illusion of a beam piercing the sky. These columns are typically white when formed by artificial lights at night but can display colors such as reddish hues during sunset due to the prevailing atmospheric conditions.[7][8] The apparent height of a light pillar can span a few to several degrees in the sky, depending on the distribution and altitude of the ice crystals aloft, while its width varies from narrow and sharply defined to broader and more diffuse. Intensity differences arise from the brightness of the source light, with brighter sources producing more vivid pillars, though the overall appearance remains ethereal and elongated.[7][9][10][8] Contrary to common misconceptions, light pillars are not solid beams of light emanating directly from the source but rather an optical illusion resulting from multiple reflections off ice crystals. They may appear to shimmer subtly if the crystals are drifting through the air, adding a dynamic quality to the otherwise static column. These phenomena are often observed in cold weather conditions where ice crystals are present in the atmosphere.[11][12][13]Physical mechanism
Light reflection process
Light pillars form through the specular reflection of light from the horizontal faces of plate-like hexagonal ice crystals or from the horizontal end faces of short columnar (pencil-shaped) ice crystals suspended or slowly falling in the atmosphere.[14] These thin, disk-shaped crystals, typically 10–50 micrometers thick, align themselves with their broad faces parallel to the ground due to aerodynamic drag as they descend through still air, similar to falling leaves or feathers. This horizontal orientation allows the flat crystal surfaces to function as miniature mirrors, efficiently reflecting incoming light rays without significant diffusion. Crystals that deviate from this orientation by more than a few degrees scatter light in multiple directions, contributing negligibly to the coherent pillar effect.[2][15] The process relies on geometric optics, where light from a low-elevation source, such as the sun near the horizon or urban lights, approaches the crystals at a shallow angle. For an upper pillar, an incident ray strikes the underside of a horizontally oriented crystal and reflects upward according to the law of reflection, with the angle of incidence equaling the angle of reflection relative to the normal of the crystal face. This reflected ray reaches the observer's eye, appearing to originate from a virtual image of the light source positioned higher in the sky. Conversely, rays hitting the upper face of crystals reflect downward, forming a lower extension of the pillar, though this is less common for elevated sources.[2][16] The vertical alignment of the pillar arises because the reflections from numerous crystals at varying altitudes remain parallel to the original light direction, creating a columnar beam that extends both above and below the source. The height and brightness of the pillar depend on the density and depth distribution of the oriented crystals, with deeper layers producing taller structures. Only crystals with precise horizontal alignment contribute to the sharp, elongated appearance, as even slight tilts broaden the reflection into a diffuse glow. These plate crystals can originate from vapor deposition in ice-supersaturated air (such as in cirrus clouds) or from the freezing of supercooled water droplets in mixed-phase clouds under cold atmospheric conditions.[15][17][14]Atmospheric requirements
Light pillars form under cold atmospheric conditions that promote the creation and suspension of ice crystals capable of reflecting light vertically. Air temperatures typically below -10°C, often between -10°C and -20°C for plate crystal formation, and colder (around -30°C or below) in high-altitude cirrus, enable the growth of thin, plate-like ice crystals, which are the primary reflectors for this phenomenon.[18][19] These crystals can develop at various altitudes: near the surface in diamond dust, within low-level stratus clouds or fog (0.1-2 km), or in high-altitude cirrus layers (5-13 km) in stable inversions.[2][10] The surrounding environment must feature clear skies to ensure visibility, with humidity conditions varying by altitude: low humidity near the ground for diamond dust to minimize scattering and ensure crystal stability, or ice-supersaturated air in cirrus layers, with minimal wind to preserve the slow, gentle descent of the plates. This stability allows the crystals to maintain a predominantly horizontal orientation as they fall, aligning their flat faces for effective light reflection.[2][20] For the pillar to appear prominent, the light source—such as the sun or an artificial light—needs to be positioned low relative to the observer, ideally with an elevation angle under 10° above the horizon. This low positioning optimizes the geometry for vertical beams, as the near-horizontal rays interact with the elevated crystals to produce the elongated, shaft-like appearance.[8][3]Occurrence and observation
Environmental conditions
Light pillars are most commonly observed during winter months in mid-to-high latitude regions, particularly between 40° and 60° N and S, where cold, clear nights and low sun angles at sunrise or sunset enhance visibility.[21][22] These conditions align with the seasonal presence of plate-shaped ice crystals suspended in the atmosphere, which reflect light vertically.[5] Geographic hotspots for light pillar sightings include polar and subpolar areas such as Canada, Scandinavia, and Siberia, where persistent subzero temperatures and long winter nights provide ideal setups for the phenomenon.[23][24] In contrast, occurrences are rare in tropical regions due to insufficient cold for ice crystal formation.[25] Favorable weather patterns involve stable high-pressure systems that promote radiational cooling and temperature inversions, trapping ice crystals near the surface in calm, windless air.[26][27] In urban settings, light pillars often arise from streetlights interacting with ice crystals in ice fog or diamond dust during cold winter nights, creating vivid beams amid cityscapes.[6][28]Notable sightings and photography
Light pillars have been observed and documented throughout history, often mistaken for otherworldly or supernatural events.[29] In modern times, light pillars continue to captivate observers and frequently go viral on social media due to their striking appearance. Urban environments also produce impressive displays; for instance, in January 2020 during a cold night near Toronto, Canada, streetlights created vivid pillars visible across the region, photographed by locals and shared extensively online.[30] More recently, in late 2024, residents in Alberta, Canada, captured pillars of light rising from the ground amid arctic air, which went viral for their surreal effect.[31] In February 2025, light pillars were widely observed and photographed across West Michigan during a period of extreme cold and snow flurries.[32] These sightings highlight how light pillars can appear in both remote and populated areas under the right winter conditions.[23] Capturing light pillars through photography requires specific techniques to highlight their vertical beams and subtle colors. Photographers advise using a sturdy tripod to prevent camera shake during long exposures, typically ranging from 1 to 30 seconds, which allows the light reflections to build intensity without overexposing the scene. Wide-angle lenses are ideal for encompassing multiple pillars or the broader sky, while shooting at twilight enhances color gradients from sources like the setting sun or city lights, adding depth to the images. Low ISO settings (around 100-400) and mid-range apertures (f/8 to f/11) help maintain sharpness and contrast in the cold, clear air where these phenomena occur.[33][34]Related phenomena
Comparisons to halos and parhelia
Light pillars differ from the 22° halo in their formation mechanism and appearance, though both are ice crystal optical phenomena. The 22° halo arises from refraction of sunlight through hexagonal columnar ice crystals, where light enters one prismatic face and exits another, deviating by a minimum of 22° to produce a circular ring around the sun or moon.[2] In contrast, light pillars result exclusively from reflection off the horizontal basal faces of plate-shaped ice crystals, generating vertical beams aligned directly with the light source and lacking any angular offset or circular geometry.[5] While the 22° halo requires randomly oriented columnar crystals in high-altitude cirrus clouds for its symmetric arc, light pillars form from gently falling, nearly horizontal plate crystals suspended at various altitudes, such as in high-altitude cirrus clouds or near the ground in diamond dust.[35] Similarly, light pillars can be distinguished from parhelia, commonly known as sun dogs, which are vivid horizontal bright spots positioned approximately 22° to either side of the sun. Parhelia occur via refraction through plate-like hexagonal ice crystals oriented with their flat faces horizontal, where light bends at the minimum deviation angle to create these offset luminous patches, often appearing as part of or enhancing the 22° halo.[2] Light pillars, however, manifest as vertical columns extending above or below the light source due to specular reflection, without lateral displacement or the prismatic color separation seen in parhelia.[5] This vertical alignment stems from the observer's line of sight catching multiple reflections from crystals at varying heights, producing a shaft rather than discrete spots. Despite these differences, light pillars, halos, and parhelia share the fundamental requirement of suspended ice crystals in cold atmospheric conditions, typically below -10°C, to interact with light.[2] Halos and parhelia predominantly involve refraction in columnar or plate crystals for angular deflection, whereas light pillars rely on reflection alone, emphasizing the role of crystal orientation—horizontal for plates in pillars and parhelia, versus varied for halos.[35] These shared ice-based origins highlight their occurrence in similar wintry environments, but the distinct optical processes ensure light pillars appear as linear extensions rather than arcs or spots.[5]Distinctions from other vertical lights
Light pillars are often mistaken for crepuscular rays, which are beams of sunlight streaming through gaps in clouds and appearing to diverge or converge due to perspective, creating a radiating pattern across the sky.[36] In contrast, light pillars form through specular reflection off the flat faces of horizontally oriented plate-shaped ice crystals suspended in the atmosphere, resulting in parallel vertical columns that do not fan out but remain aligned directly above or below the light source.[5] Crepuscular rays arise from scattering by haze or dust in cloud-free corridors, lacking the crystal-mediated reflection that defines light pillars.[37] Unlike direct artificial light beams such as those from searchlights or lasers, which produce coherent, narrow, and precisely directional columns of light originating from a single point and propagating without atmospheric mediation, light pillars are diffuse and result from multiple reflections by ice crystals at various altitudes.[38] Searchlights and lasers maintain their intensity and focus over distance due to low divergence, whereas light pillars exhibit varying brightness with height, fading as fewer crystals are present higher in the atmosphere, and their appearance depends on the distribution of ice crystals rather than the source's beam characteristics.[39] Light pillars differ fundamentally from the aurora borealis, where charged solar particles excite atmospheric gases to produce dynamic, colorful displays such as arcs, curtains, or rays that shift and fluctuate over time. Aurora emissions occur high in the ionosphere from geomagnetic activity, often displaying greens, purples, and reds independent of ground-based light sources, while light pillars are static, vertically oriented reflections mirroring the color and position of a local light source like the sun, moon, or urban lights.[41] Similarly, zodiacal light emerges from sunlight scattering off interplanetary dust particles along the ecliptic plane, forming a broad, faint, triangular glow tilted to the horizon that follows the sun's path and is best seen in dark twilight skies away from local pollution. This diffuse zodiacal emission lacks the sharp verticality and direct tie to terrestrial ice crystals or specific low-altitude light sources that characterize light pillars.[42]References
- https://science.[nasa](/page/NASA).gov/solar-system/skywatching/night-sky-network/nsn-night-lights/