The Aurora Borealis in "Polaris"

Well do I remember the night of the great Aurora, when over the swamp played the shocking corruscations of the demon light. After the beam came clouds, and then I slept.

And it was under a horned waning moon that I saw the city for the first time.
_____

The third sentence mentions a "horned waning moon", which precisely matches data for late on the 7th of March, 1918. Of course this is a typical situation each and every lunar cycle. However, that evening was a night of low moonlight.

The "horned moon" can be coraborated in two sources, one calculated (briancasey.org), and one contemporary (Armour's Almanac 1917 for 1918). You will see (click to expand images below) that in Boston, the last quarter Moonwas 5 March 1918 at 5:44 AM. New Moon was 12 March 1918 at 2:52 AM.

However, why is 7 March such an interesting date? It was the date of a spectacular aurora borealis that dazzled New England and shorted out telegraphs. The product of solar flares, the energy is tremendous as it interacts with Earth's magnetic field. This one was a "hum-dinger". Between about 9:45 PM and 11:00 PM on 7 March 1918 the electric wires sizzled. The NYT article is below. Conveniently, Popular Astronomy received a Massachusetts report on the visual giving as close as what Lovecraft would have seen from his window or outside if he ventured into the cold (note snow on ground).

There is a slight complication, as that on 5 April 1918 another Aurora was seen of less intensity. That report is also listed below.

A star map from Popular Astronomy for March 1918 is included with green sketching (by Chripy) for the aurora (above). Polaris is marked in red. It runs right through Charles' Wain (wagon), also known as ursa major and the big dipper. Polaris is part of the "little dipper". One supposes that while Lovecraft was writing Polaris, he recalled the aurora and impulsively mentioned it.

To date, Chripy has not seen a definitive dating of Polaris. However, Darrell Schweitzer in Discovering H.P. Lovecraft (p. 75) states that "'Polaris' seems to have been based on a dream Lovecraft had in Spring of 1918, which is related in some detail in letter 34...". (i.e. to Maurice Moe, 15 May 1918, "...several nights ago ..." HPL had a dream about a city.] S. T. Joshi and David E. Schultz in An H.P. Lovecraft Encyclopedia mentions that it was written in late Spring or early Summer 1918 using the letter as a terminus date. This is repeated in The Dreams in the Witch House and Other Weird Stories (2004).

Whether seeing the aurora in March, or even in April, stimulated the subsequent dream in May, Lovecraft clearly had this event in mind and forced the connection to the star Polaris.