Researchers have reconstructed solar activity back to the year 969 using measurements of radioactive carbon in tree rings. Those results help scientists better understand the dynamics of the sun and allow more precise dating of organic materials using the C14 method. What goes on in the sun can only be observed indirectly. Sunspots, for instance, reveal the degree of solar activity—the more sunspots are visible on the surface of the sun, the more active is our central star deep inside. Even though sunspots have been known since antiquity, they have only been documented in detail since the invention of the telescope around 400 years ago. We also now know that the number of spots varies in regular eleven-year cycles and that, there are long-lasting periods of strong and weak solar activity, which is also reflected in the climate on Earth.