Galactic Winter

I wonder if anyone has considered the possibility that drastic climatic changes on Earth ["Abrupt Climate Change," by Richard B. Alley] have been and will be influenced by something far beyond. Could it be that as our solar system orbits our galaxy's center, it, along with our planet, might travel through one of the many clouds of particles and debris, dimming the sun enough to cause a sudden ice age? Conversely, the climate would warm when we emerged from the cloud.

Robert F. Wilson Kingman, Ariz.

BALANCING ACT: A dramatic shift in Earth's climate may occur suddenly and unpredictably.

ALLEY REPLIES: A big meteorite like the one that killed the dinosaurs would have a great effect for some years, and it remains possible that the extraterrestrial environment weakly affects climate over many timescales, but the weight of evidence points to most of our climate variability as homegrown.

Many scientists share Wilson's interest in possible extraterrestrial causes of climate changes. One approach looks at variations over time in the rate at which meteorites or other objects have reached Earth. Some suggest that data show time variations in extraterrestrial flux correlated with climate changes over tens of thousands to hundreds of millions of years, but I believe most researchers consider these results tenuous at best.

A weak role for the sun remains possible for some changes over thousands of years and shorter. A strong variation in Earth's magnetic field allowed more cosmic rays to reach its surface around 40,000 years ago, as documented by the odd isotopes they produced, but the climate was largely or entirely unaffected by the event, so cosmic rays do not seem especially important.

CEREBRAL HARMONY Norman M. Weinberger's article, "Music and the Brain," brought to mind Pythagoras of Samos, who was the first to explore music mathematically and experimentally. Specifically, he discovered that the most harmonious musical intervals are created by the simple numerical ratios of the first four integers that derive, respectively, from the relations of string length: the eighth, the fifth, the fourth.

Constantine J. Vamvacas

Athens, Greece

ERRATA In "Music and the Brain," by Norman M. Weinberger, research showing that infants prefer consonance to dissonance should have been attributed to Laurel Trainor of Mc-Master University, instead of Sandra Trehub of the University of Toronto. Also, the ratio for a minor second (for instance, C-sharp to C), used in studies of dissonance, was incorrectly stated as 9:8, which refers to a major second (for example, D to C). Depending on the particular type of scale used, the ratio is closer to 19:18, for example, 17:16.

In "What's In a Name?" by Christine Soares [Insights], it was incorrectly stated that members of the Chordate phylum must have a backbone. Members must have a notochord at some time during their development.

In "Computing at the Speed of Light," by W. Wayt Gibbs, the element phosphorus was incorrectly identified as phosphate.

50, 100 & 150 Years Ago

Renewable Energy

Renewable Energy

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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