Sun Moon Planet and Artificial light pillars
Near sunset when the sun is low. Or minutes or even an hour afterwards depending on where you are and the season. Above the sunís position an apparent column of light shining upwards. reaching up to half to even to the whole width of an outstretched hand at armís length. I enjoy them most after sunset. Then as twilight thickens they they creep slowly northwards. Always keeping themselves over where the sun sinks ever deeper beneath the horizon.
See that in reverse before and after dawn. See them with a bright moon. See many at once over bright lights.
Pillars, and yet not pillars.
Pillars they are certainly not. Well, perhaps in the mind's eye but never in any real physical sense. Not at all are they beams of upward or downwards light. You could fly around and chase them in the skies but would never find thos fictional light beacons.
Only seen in the freezing weather of northern parts - or the frozen lands of the south? Not so. Search and you will see them anywhere on the planet. But it must be confessed that the finest are during subzero temperatures. Then their ice crystal authors come to ground level as diamond dust that sparkles and pricks the skin.
They are a type of ice halo. Flattish plate shaped crystals make most - but not all - of them.
The crystals float in high cirrus and altostratus clouds or as diamond dust near the ground. Downwards motion relative to local air currents aligns them horizontal. A myth is that the crystals are falling from the clouds. They rarely do that, they only drift in the cloud and that can be upwards as well.
The best and tallest pillars come from large, imperfect and wobbly plates. Their large roughly horizontal faces act as tiny mirrors and reflect the sun to us - they glint. Millions of glints appear as a pillar shape. Yet there is no pillar for the crystals can be at a whole variety of distances and heights.
We see a few very tool and straight pillars reaching up 22į to a bright upper tangent arc. Upper tangent arcs are made by columnar crystals floating with their long axes horizontal. Could these unusual pillars be made by the same crystals. It seems counterintuitive - where are the near horizontal mirrors?
The answers came from the early pioneering ray tracing research of Robert Greenler and colleagues. Column crystals can rotate about a vertical axis plus a second horizontal axis passing along the column. The combination of the two rotational freedoms results in the crystalís long side faces being close to horizontal than at any other angle! Near horizontal wobbly mirrors again.
Any light can make a pillar. A bright moon in a dark sky is the easiest to see. Venus has pillars.
Moving back to Earth, we still have a predilection for unshielded lights, wasting energy, dazzling, trespassing on neighbours and dimming the stars. In cold weather when there is low or ground level diamond dust they also make wonderful pillars. Put the lamp nearby and its rays are no longer parallel and we have divergent light pillars that have a strange solidity and sometimes strange shapes.