By Jim Kaler

Though it provides almost all our energy, however indirectly, we don't pay much attention to the Sun. And we shouldn't, as unfiltered sunlight is dangerous to look at. Gaseous throughout, nearly 100 million miles away, almost a million miles across, 330,000 times Earth's mass, made almost entirely of hydrogen and helium, it radiates 400 trillion trillion watts into space. At the solar center, the temperature hits 16 million Celsius, the density a dozen times that of lead, more than enough to run a nuclear engine within the deep solar core that produces the solar energy, as it has since the Sun's birth 4.6 billion years ago. The energy is eventually released from the 5600 Celsius surface as a soft yellow-white light. Only a small bit of high-energy ultraviolet light, which causes sunburns, gets through the Earth's protective atmosphere.

The Sun rotates in just under a month, but slower at the poles than at the equator. The surface also roils with up and down convection. The two motions combine to generate intense magnetic loops. Where the loops enter and exit the surface they block the upward gaseous flow and chill localized patches into dark sunspots. Ephemeral, the spots last for mere days to a month, the largest easily capable of swallowing the Earth. This magnetic energy is transferred to the solar "corona," a thin surrounding gas heated to two million Celsius. The corona is so faint that it's visible only when the bright solar surface is covered by the Moon during a total solar eclipse. The corona is the seat of the solar wind, a high-speed flow of atomic particles that pervades the Solar System and that stops only when it rams into the interstellar gases three times farther out than Pluto.

The huge magnetic loops can connect with one another, which causes their collapse. Where magnetically trapped particles hit the solar surface, they produce powerful solar flares. The disappearance of magnetic support also releases blobs of coronal gas. Travelling for a couple days, if the blobs hit the Earth, they disrupt our protective magnetic field (generated in the Earth's fluid iron core), which allows energetic atomic particles to be dumped into the upper atmosphere. The result is a grand display of northern lights that can reach well into temperate latitudes, making the sky to seem to be on fire. The electrical energy can also play havoc with orbiting satellites and power distribution systems. In 1987 a coronal mass ejection shut down the power grid in Quebec. "Space weather" has become so important that we have sentinel satellites to monitor it. Solar magnetic activity with all its aspects comes and goes on an 11-year cycle. Similar cycles have been detected on stars like ours. As the solar wind spreads outward it drags the solar magnetic field with it, which gradually slows the Sun down, diminishing the solar magnetic energy. So enjoy them now, as over the next few billion years the northern lights will cease to be.

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Copyright © James B. Kaler, all rights reserved. These contents are the property of the author and may not be reproduced in whole or in part without the author's consent except in fair use for educational purposes. First published in the April-June 2015 Clark-Lindsey Village Voice.