Red sky

Thurs­day (23 Janu­ary) was one of tho­se rare pur­ple days. It real­ly is rare. When this light comes, it seems to hap­pen pre­fer­a­b­ly during the polar night, as it is coming near the end, as was the case on 10 Janu­ary 2018, when the­re was an artic­le about it in Sval­bard­pos­ten.

It pro­ba­b­ly hap­pens less than once a year that the sky turns red in such a magni­fi­cent way. Yes­ter­day was one of tho­se days when you can count yours­elf lucky if you’re in the right place. And even more so if you’re able to spon­ta­neous­ly drop the ham­mer and head out into Advent­da­len with your came­ra, away from the arti­fi­ci­al light.

A few impres­si­ons:

Click on thumb­nail to open an enlar­ged ver­si­on of the spe­ci­fic pho­to.

The colour of the pho­tos real­ly cor­re­sponds to the impres­si­on you got on the spot.

The phy­sics of the red sky

In the Sval­bard­pos­ten artic­le lin­ked abo­ve, Dag A. Lorent­zen, then as now pro­fes­sor of geo­phy­sics at UNIS, explains the phe­no­me­non by the refrac­tion of sun­light in high atmo­sphe­ric lay­ers, at an alti­tu­de of about 20 kilo­me­t­res. Howe­ver, the meteo­ro­lo­gi­cal con­di­ti­ons must be just right: The­se include a very cold atmo­sphe­re in the­se lay­ers of air and the for­ma­ti­on of spe­cial clouds that refract the light in exact­ly the way that pro­du­ces this colou­ring. The­se ‘clouds’ them­sel­ves are not visi­ble; they are weak con­cen­tra­ti­ons of ice crys­tals rather than what is com­mon­ly thought of as clouds. In this case, the parts of the spec­trum from vio­let to green are most­ly lost due to refrac­tion and scat­te­ring, lea­ving the remai­ning wave­lengths (main­ly red) to domi­na­te.

The actu­al cir­cum­s­tances must be so exact that the phe­no­me­non of the ‘red sky’ is so rare. In my opi­ni­on, the colour impres­si­on is more vio­let, but as the vio­let part of the spec­trum of visi­ble sun­light is the first to be lost, the term red is pro­ba­b­ly more appro­pria­te from a phy­si­cal point of view.

Pur­ple haze

The appro­pria­te sound­track is of cour­se ‘Pur­ple Haze’ by Jimi Hen­drix 🙂.

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