Was this an astronomical phenomenon observed in 1689? In a Swedish church record from 1689 a phenomenon in the sky is described. With my very limited understanding it could be a meteorological or an astronomical phenomenon, so here I ask if it could have have an astronomical phenomenon, and what it was in that case.
The place
The observations were made from the village of Fagerhult in Kalmar län in Sweden, at 57°08′55″N 15°39′52″E, in the sky to the North-East.
The time
This was 18 December 1689 (according to the Gregorian calendar – actual date given in the document is Julian 8 December).
It was &quot;around 4 in the afternoon, around sunset&quot;. (I think that sunset actually was at about 3:15 PM local time.)
Description
It is described as an elongated cross with the long arm being about 6 times as long as the short arm. I think it means to say that the long arm was vertical, but I'm not sure about that. The cross was shining clearly on the sky, a burning light in the north-east for about an hour. It was almost a clear sky and where the cross was there were no clouds at all.
The account is accompanied by this illustration. It doesn't have the same proportions as I understand the text to say. Maybe the image is better than the text.


(Undoubtely this led to religious ponderings, and that was presumably why this was recorded, but there is actually nothing of that in the note – just this description.)
Was there anything special happening in the sky then that could have to do with this?
This is a really interesting question!  One thing to note is that since it appeared in the northeast at sunset, it is nowhere near the sun - in fact, it is pretty much in the opposite direction as the setting sun.  In the winter in the north, the sun would set in the southwest.  And regarding your comment about the text describing the event as &quot;around sunset&quot; when it would have been 45 minutes later, I think that's not surprising - at northern latitudes in the winter, around the winter solstice, the path of the sun is at a very oblique angle to the horizon, so twilight lasts quite a long time.  So it could easily feel like &quot;sunset&quot; for an hour or more.  Though the sun set at 3:15 PM as you note, at 4:00 PM the sun would still only be 5.3 degrees below the horizon, so civil twilight had not yet ended. Plus, no one in those days was wearing a wristwatch, so a given observer's estimate of time of a particular event may have been less precise than we would be accustomed to now.
So, my best guess is that this might have been related to anticrepuscular rays.  Pros and cons for this hypothesis:
Pros:

Appears at the right time of day, in the right location (opposite the setting sun).
Would give a vertical ray.
Doesn't need clouds in the direction that the image is seen.  (But see my comment below about the crossbar.)

Cons:

Most of the cases I can find pictured have multiple rays, which isn't what is described here.
There is no obvious explanation for the horizontal part of the cross.
I'm not sure if this would persist without obvious changes for as long as described.

Another thought I had, which looks very similar in appearance, but is in completely the wrong direction, is a sun pillar, combined with a stratus cloud, like this (from here):

The appearance is striking, but (a) it would have to be in the sunset direction, and (b) there would have to be clouds.  So it doesn't seem to quite work.
I also thought of the moon, and whether that could give something similar, e.g. if it was just below the horizon.  But that doesn't quite work, either.  I did some calculations, and the moon was 38% full that day (waxing crescent, one day short of first quarter).  At 4:00 PM (assuming that the location is UTC+1 hour), the moon would have been 23 degrees above the horizon, at an azimuth of 161 degrees, i.e. low in the south-southeast.  So that doesn't seem like it would contribute much to something in the northeast.
So clearly I don't have a definitive answer, but maybe something here will be helpful or give others some ideas.