Constraints on Long-Term Variations in the Solar Luminosity

Steve Spangler, PhD

The average temperature of the Earth has risen 1.0 – 1.5 K since the late 19th century. It is generally agreed that much or all of this warming is due to increases in the atmospheric carbon dioxide content caused by fossil fuel burning. However, in the geological record, there are numerous cases of climate warming (and cooling) which obviously were not caused by human activity. One possible explanation for these other events is variation in the luminosity of the Sun. Variations of the order of one to several percent could have significant climatic consequences. One way to constrain or measure such variations is to measure the spread in luminosities of solar-type stars in an open star cluster. Open star clusters are groups of a few hundred to a couple thousand stars that were born at the same time and with the same chemical makeup. A measurement of the dispersion in stellar luminosity must be corrected for effects such as unrecognized binary companions and the effect of measurement error in stellar brightness. I describe progress made in these areas, and discuss the current status of limits on luminosity variations.

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