The Spörer Minimum is a hypothesized 90-year span of low solar activity, from about 1460 until 1550, which was identified and named by John A. Eddy in a landmark 1976 paper published in ''

Science Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...

'' titled '' "The Maunder Minimum"''.Eddy, J. A., "The Maunder Minimum", ''Science'' 18 June 1976: Vol. 192. no. 4245, pp. 1189–1202PDF Copy
It occurred before

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 ...

s had been directly observed and was discovered instead by analysis of the proportion of

carbon-14 Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...

tree ring Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...

s, which is strongly correlated with solar activity. It is named for the German astronomer

Gustav Spörer Friederich Wilhelm Gustav Spörer (23 October 1822 – 7 July 1895) was a German astronomer. He is noted for his studies of sunspots and sunspot cycles. In this regard he is often mentioned together with Edward Maunder. Spörer was the first ...

. The Spörer Minimum (1420 to 1570), named after the German astronomer Gustav Spörer.

History of solar activity

Solar variation 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 surfac ...

can be quantified using sunspot counts, but this measure is only reliable for periods after records of sunspot observations were routinely made by western astronomers. For periods before sunspot records, solar activity can be found from

proxy Proxy may refer to: * Proxy or agent (law), a substitute authorized to act for another entity or a document which authorizes the agent so to act * Proxy (climate), a measured variable used to infer the value of a variable of interest in climate re ...

methods, most notably the production of radioisotopes in the Earth's atmosphere from interaction with

cosmic rays Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

, which are modulated by the solar activity. The carbon-14 method used by Spörer to identify the minimum makes use of the fact that high solar activity is correlated with low production of carbon-14 in the atmosphere. Wilfried Schröder published a table of observed

aurora borealis An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of br ...

during the Spörer Minimum which showed that the solar cycle was active. Miyahara ''et al.'' likewise found the 11-year solar cycle was still prominently detected in the carbon-14 record even during the minimum. The amplitude of the 11-year cycle seems to have been modulated only from 1455 to 1510. Jiang and Xu look at sunspot records and aurora sightings from China during the period and suggest that a minimum from 1450 to 1560 is specious. They suggest dates for the sunspot minimum of 1400 to 1510.Yaotiao Jiang and Zhentao Xu, "On the Spörer Minimum", ''Astrophysics and Space Science,'' Jan. 1986, ''Vol. 118'', 1-2, pp 159-162
Abstract and link
(accessed 12 July 2015)

Possible correlation with climate

Like the subsequent Maunder Minimum, the Spörer Minimum coincided with a time when Earth's

climate Climate is the long-term weather pattern in an area, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorologic ...

was colder than average. This correlation has generated hypotheses that low solar activity produces cooler than average global temperatures, although Jiang and Xu point out that while the period 1430-1520 (starting slightly before the Spörer minimum) was indeed colder than average in China, the period 1520-1620 (the second half of the minimum) was warmer than average. A specific mechanism by which solar activity results in

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

has not been established, One theory is modification of the Arctic Oscillation/North Atlantic Oscillation due to a change in solar output.

References

{{DEFAULTSORT:Sporer Minimum 15th century 16th century History of climate variability and change