By Dr David Whitehouse
BBC News Online science editor
Reduced solar activity in the 17th Century may be the reason for the perfect sound of Stradivarius violins.
"The Messiah": The Sun's output may have been key to its qualities
Scientists from Columbia and Tennessee universities in the US say the Sun's declining output at that time resulted in colder winters and cooler summers.
This produced slower tree growth which in turn led to denser wood with superior acoustical properties - circumstances not repeated since.
Today, musicians and collectors will pay many thousands for a Stradivarius.
There is still considerable debate about why the violins made by Antonio Stradivari sound superior to modern-day violins.
Born in 1644, he established his workshop in Cremona, Italy, and remained there until his death in 1737.
During his lifetime, it is estimated he made 1,100 instruments - violins, guitars, violas, and cellos - of which about 600 survive today.
Stradivari is responsible for crafting the most celebrated violin in the world: "The Messiah" in 1716. But what makes these instruments so prized?
The popular belief is that the Cremonese artisans of the late 17th to 18th Centuries had a "secret ingredient" (or undocumented technique) that gave the instruments their famed sound.
Candidates include the use of a special varnish, chemical treatment of the wood, "cooking" or drying the wood, wood seasoning, and the use of very old wood from historic structures.
But two US scientists think the answer can be found in the Sun.
Stradivari was born one year after the start of the so-called Maunder Minimum - a period between 1645 and 1715 when our star went through a decline in activity and output.
During this period, sunspots were rarely seen on the Sun, and the 11-year solar cycle that is so prominent today was closed down.
The Maunder Minimum coincides with what climatologists call the "Little Ice Age", a period of very cold weather in western Europe.
Estimates of the cooling during this time range from 0.5 to 2 deg Celsius.
Evidence for the cold spell is found in tree-ring records from high-elevation forests in the Alps. There was a long period of reduced growth rates, and when trees grow slowly their wood is denser.
Writing in the journal Dendrochronologia Lloyd Burckle, of Columbia University, and Henri Grissino-Mayer, of the University of Tennessee, say that the long winters and cool summers of the period produced wood that gave the unique, rich sound of the Cremonese instruments.
They point out that violin makers have always known that the selection of the wood makes all the difference to the sound of the instrument. Maple is preferred for the back, ribs, and neck, while spruce is preferred for the top.
Stradivari and other eminent Italian violin makers of the 17th and early 18th Century who worked in Cremona probably used the nearby forests of the southern Italian Alps as their source of spruce wood.
It seems that the trees growing during the lifetime of Stradivari experienced a unique set of environmental conditions that has not occurred since.