Earth's poles feel warmth of the full moon.

Romantic souls who bathe themselves in lunar light run little risk of developing a moonburn. Yet the full moon is strong enough to alter weather on Earth, according to a study of daily temperatures over the last 17 years.

Satellite measurements of air temperature in the lower atmosphere reveal that the polar regions are 0.55#161#C warmer during a full moon than during a new moon, report John A. Shaffer, Randall S. Cerveny, and Robert C. Balling Jr. of Arizona State University in Tempe. The moon has no appreciable effect on tropical temperatures, note the researchers, who describe their work in the Jan. 1 Geophysical Research Letters.

Shaffer and his colleagues say they were surprised by the amount of polar warming because the moon lies closer to the tropics and should influence this region more than the poles. "We're unsure of the exact mechanism that is causing [the warming]," says Shaffer.

Meteorologists have long attempted to draw connections between the moon and weather on Earth. Two years ago, Balling and Cerveny reported that global temperatures appear to follow the lunar phase, with Earth's average temperature rising by a very slight 0.02#161#C at the time of a full moon. When they later sifted satellite data by latitude, the researchers found that polar warming is 25 times the global average at the time of a full moon.

The midlatitudes show an opposite response, growing slightly warmer during the new moon and cooler during the full moon.

Although they cannot yet explain the connection between lunar cycle and polar temperature, Shaffer and his coworkers say that the clear polar air may let in more light from the full moon than other parts of the atmosphere do. They also speculate that tidal forces may generate waves in the atmosphere and shift heat around the globe. Alternatively, the tug of the moon on the atmosphere could compress and heat the air at the poles more during a full moon.

John R. Christy of the University of Alabama, Huntsville, who maintains the data set of satellite measurements, cautions that the effect may be an artifact of the way the satellite measures atmospheric temperatures. If there is some unintended reflection of lunar light off a piece of the spacecraft, the full moon could skew the temperature data, warns Christy, who adds that he sees no evidence of such a problem.

If the moon does warm polar regions significantly, it would present a new puzzle for atmospheric scientists. "The finding would say that the climate system is sensitive in ways that we had not expected it to be," says Christy.

Any explanation of the lunar effect will need to account for why the full moon has an opposite influence on midlatitudes and on polar regions. The Arizona State researchers are also examining satellite measurements of the stratosphere to see if temperatures in this region respond in sync with those in the lower atmosphere.

Some scientists question whether polar temperatures truly swing up and down with the lunar cycle. Thomas R. Karl of the National Climatic Data Center in Asheville, N.C., says he would like to see the finding verified by studies of ground-based temperature measurements.