Solar cycle 15 was the fifteenth
solar cycle
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfa ...
since 1755, when extensive recording of solar
sunspot
Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sun ...
activity began.
The solar cycle lasted 10.1 years, beginning in July 1913 and ending in August 1923. The maximum
smoothed sunspot number
The Wolf number (also known as the relative sunspot number or Zürich number) is a quantity that measures the number of sunspots and groups of sunspots present on the surface of the Sun.
History
Astronomers have been observing the Sun recordi ...
observed during the solar cycle was 175.7 (August 1917), and the starting minimum was 2.5.
[SIDC Monthly Smoothed Sunspot Number.]
During the minimum transit from solar cycle 15 to 16, there were a total of 534 days with no sunspots.
[Spotless Days.]
[Solaemon's Spotless Days Page.]
History
Geomagnetic storms in March 1918, August 1919, October 1919, and March 1920 affected telegraph lines, while a solar flare on 13 May 1921 also affected rail signal and switching equipment, in what was known as the "New York Railroad Storm."
1921
A
May 1921 geomagnetic storm, major geomagnetic storm during 13–15 May 1921 caused damage in communication systems and aurora displays in much of the eastern United States.
In
Sweden
Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
, the event caused major disruptions to the telephone exchange in
Karlstad
Karlstad (, ) is the 20th-largest city in Sweden, the seat of Karlstad Municipality, the capital of Värmland County, and the largest city in the province Värmland in Sweden. The city proper had 65,856 inhabitants in 2020 with 95,167 inhabitants ...
and in the early morning of May 15, the building burned down.
Witnesses described the telephone cables going into the building as glowing.
See also
*
List of solar cycles Solar cycles are nearly periodic 11-year changes in the Sun's activity that are based on the number of sunspots present on the Sun's surface. The first solar cycle conventionally is said to start in 1755 when Rudolf Wolf began extensive reporting o ...
References
Solar cycles
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