An important result from existing computer models is that, whatever physical mechanism is operating to modulate the energy output of the Sun, its effects will be evident in certain global parameters, such as the size of the Sun (diameter), its shape, and the solar luminosity.
If the solar diameter is linked to changes in the internal structure of the Sun, then historical records could be used to provide information on past variations of the solar luminosity. The historical changes of the solar diameter reported to date have a minimum-to-maximum variation of about 2 arc seconds (1 arc second 726 kilometers 451 miles; the solar diameter is 1920 arc seconds), and a period of about one century.
On longer time scales of 10,000 years or more, a rather complete record of solar activity is contained within carbon-14 and beryllium-10 isotope deposits on the Earth (tree rings and ice cores). After the terrestrial effects are removed from these records, a clear correlation is observed with the 11-year sunspot cycle. On longer time scales, there are characteristic periods of about 80, 150, 200 and 500 years (and longer). If these isotope records truly reflect past solar magnetic activity, and their magnitudes can be interrelated over the period of overlapping measurements, then a substantial record of past solar irradiance change could, in principle, be constructed.
Approved by Peter Fox
Last revised: Wed May 17 11:28:21 MDT 2000