The ball lightening of April 17, 1939


Ball lightening is a very rare phenomenon which to this date is hardly understood. It may therefore be of interest to call attention to a description of the phenomenon given by the Danish astonomer Carl Luplau Janssen which he published in the popular magazine Urania, November 1943, page 24-27. Luplau Janssen had studied astronomy at the University of Copenhagen and from 1919 to his death i 1966 he owned the Urania Observatory in Frederiksberg, a suburb of Copenhagen. He was a well-known public figure who gave talks on astronomy, wrote many popular books and demonstrated celestial objects for high school classes and the public in general. Between 1943 and 1965 he, almost solehandely, published the astronomy magazine Urania (of which he himself wrote the major part). He was a trained observer, so his account, which I have translated below, can be relied upon.


The ball lightening of April 17, 1939.

   Ball lightening is a rather rare event, and although we possess a few hundred more or less accurate accounts from many countries of this oddity of nature, we do not know very much about its nature and origin. On April 17, 1939, the author of these lines had the opportunity to observe a typical ball lightening at close range. The description of this meeting given below is the first one in print made be the observer himself.

Movement of the ball lightening

Plan of the first floor of the Urania Observatory. Upper left: Observatory with refractor and position of Mr. Luplau Janssen (A). Upper right: Library with radio and stove. Lower right: Kitchen with position of Mrs. Aase Luplau Jansen (B). Lower left: Sleeping room with telephone (!). Center: Passage with staircases to lower level. Dottet line: Path of ball lightening.

   The ball lightening appeared at the Urania Observatory, which is located on Dronning Olgas Vej 25 [Queen Olga's Road], Frederiksberg. The altitude is about 10 meters above sea level. The distance to the sea is about 3 km, maybe a little more. The sketch above shows the location of the rooms on the first floor, where the drama took place, if such a dramatic term may be used. The large square room at left is the observatory which is covered with a zink-clad [cylindrical] dome. The height of the top of the dome from the floor is about 6 meters and the room measures about 5 meters on each side. In the middle of the room is the mounting which carries the telescope, the length of which is 4.20 meters. In the dome there is a slit one meter wide; it is composed of two sets of shutters, one pair in the side wall and another in the roof. These shutters are opened for observations. To the left of the observatory room lies the library and to the north the sleeping room. From these rooms doors lead out to a short passage running east-west. At the west end of the passage there is a door leading to the kitchen. The sketch also indicates the positions of telephone, radio receiver, the sole stove of this level as well as the position of the two observers. Now the following happened.

   Mrs. Luplau Janssen was busy in the kitchen, the writer was located in the observatory where the shutters were open, pointing towards the southwest. The telescope was in a horizontal position, pointing east-west. All doors were open. Light was lit in the passage and in the kitchen, the radio was playing, but the stove, which had been thoroughly cleaned the same morning, was not in use. Another remark must be made. The shutters in the roof are opened from the floor of the observatory with two iron rods which are connected to two levers, one for each shutter. Part of the weight of the shutters is balanced by two iron cylinders, hanging from the ends of said levers. When the shutters are open, the two iron rods hang freely down the room about 3/4 of a meter from the vertical frame of the shutters.

Door covered by the ball lightening

Door from the observatory into the passage.
During the passing by of the ball ligthening, Luplau Janssen was standing at the position of the chair.
[The lettering on the door warns: "Mind the step!"]

   The sky was partly overcast, but not typically thunderous. The writer was busy lacquering a chair and had moments ago opened the roof shutters to take advantage of the dwindling daylight. Before this neither lightening had ben seen nor thunder been heard, nobody had been thinking about a storm being imminent, the more so because it was early in the year so the season for thunder was not in. Everything was calm and quiet, the time was now about 19,45.

   The writer had just finished his lacquering work, having put aside the pait brush and standing admiring his finished work, when all of a sudden a loud, crackling sound was heard, evidently comming from above. The writer turned his head, looked up to the shutters and saw long sparks shooting out from the counterweights on the levers of the shutters. This went on for about 3 seconds, when suddenly a floating glowing ball appeared in the middle of the opening approximately 1 meter above the horizontally placed telescope tube. It moved with a moderate speed downwards towards the door to the corridor. Immediatly the writer started counting seconds. It took the fireball about 6 seconds to cover the 8 meter long path through the observatory, so the speed must have been about 1 1/3 meters per second. The fireball now passed the writer at a distance of about 1 meter moving about 1 meter above the floor and passed out the door into the corridor. When it passed the door it was noticed that the sphere just covered a warning painted on the door: »Mind the step!». It just covered this text and must therefore have had a diameter of about ½ meter. It was egg-shaped with the pointed end trailing. The color in front was reddish and on the back bluewhite. From the kitchen Mrs. Luplau Janssen saw the ball lightening approach and turn off into the library. The writer followed into the passage, where nothing could be seen. At the same moment two roaring cracks were heard from above. This ended the phenomenon. It turned out that telephone and radio as well as all ellectrical installations in the house were completely intact. The only thing which resulted was that both the stove's doors had been forced open and large quantities of ash and soot had been dispersed over the library. Clear melting marks were found just above the feeding door of the stove. It is evident that the ball lightening from entering the house through the roof opening has followed the draught and ended its path at the tip of the chimney, from the stove first following a horizontal, then a vertical piece of chimney pipe.

   These observations can be supplemented with the following ones: Several neighbours saw two fireballs rising from my chimney and as rockets burst high into the air. Several others have seen the ball on its path down to the observatory, which rules out the possibility that the ball lightening should have formed in the roof opening, which was my first impression. Apparently the ball lightening followed the air current. The fact that the color was red in front, suggests that it was an effect propagating through the air, which was heated gradually when the effect passed by. The phenomenon left no smell and was not accompanied by any sounds whatsoever, apart from the initial cracking sound and the effectful finishing bang.

   Immediatly after the appearance of the ball lightening, a short, but strong thunderstorm broke out and the rain came pouring down. In all the exitement the open roof shutters were forgotten, so that more water than desired entered the observatory. Result: a large job mopping up. I saw it as my duty to notify the Meteorological Office under whose domain this phenomenon belonged. As a result, it came to the attention of the press and got on the radio news.

   This ends the account of the impressive evening at the Urania Observatory on April 17, 1939.

C. Luplau Janssen.



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Opdateret den 18.08.2006