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Soundings: Connection between the Earth and the Sun

The sun is a nuclear fusion furnace. Within the heart of the sun, simple nuclei – nuclei of hydrogen atoms – bond together to make heavier ones: helium nuclei. Making heavier nuclei releases energy.

For nuclei to fuse – to bond – they’ve got to get exceedingly close. But hydrogen nuclei carry a positive electrical charge, and repel each other like mad (only opposites attract).

Nuclei can be forced into close proximity by smashing them together so hard – so fast – that they get close and bond before their mutual repulsion can make them fly apart.



To make nuclei fly that fast, you’ve got to get them hot.

The center of the sun is 28 million degrees Fahrenheit. The pressure is such that hydrogen is squeezed 14 times denser than lead. So hot, and so dense, nuclei fly fast enough, and collide often enough, to fuse. Energy, released as gamma rays, makes its way slowly toward the surface.




A bit over a hundred thousand miles out from the center of the sun (a quarter of the way from the center to the surface), the temperature drops to 14 million degrees or so. Density drops, too.

Temperature and density can no longer keep the fusion reaction going – the starfire dies out, but the energy keeps moving.

Continuing out toward the surface, the sun’s temperature continues to drop: From a gamma-hot 14 million degrees, it drops to a white-hot 9,600 degrees at the surface.

The light from the white-hot surface of the sun, and from the higher and hotter solar atmosphere, bathes the solar system in every color of the electromagnetic spectrum, from radio to infrared to visible to ultraviolet to X-rays.

But for our atmosphere, this radiation would make life on Earth’s surface impossible. X-rays, absorbed by atoms in the uppermost air, shatter those atoms into ions and electrons (creating Earth’s ionosphere, the electromagnetic mirror that bounces distant AM radio signals around at night, absorbing them by day).

Ultraviolet penetrates deeper, until it’s absorbed by molecules of ordinary di-atomic oxygen in the stratosphere. These molecules are shattered into individual oxygen atoms (which combine with di-atomic oxygen to form tri-atomic oxygen – ozone – which absorbs yet more ultraviolet.

Hotter than fire, few of the ions at the sun’s surface carry electrons. The sun is a soup of electrically-charged atomic fragments, mostly protons (hydrogen nuclei) and electrons: a plasma.

Were they standing still, protons and electrons wouldn’t do much more than attract or repel one another. But when they’re in motion, charged particles generate magnetic fields (a radio transmitter creates radio waves by shuttling electrons to and fro).

Were they standing still, protons and electrons wouldn’t respond to magnetic fields. But when they’re in motion, charged particles are pushed and pulled by such fields, this way and that (the beam of electrons that paints the picture on a TV screen is steered by magnetic fields).

Currents – “rivers” – of plasma in the sun flow in many directions, creating a complex web of magnetic fields … magnetic fields that, in turn, steer the plasma currents this way and that. Jets and arches of plasma shoot upward and fall back. Millions of tons of plasma explode off the sun and plow through the solar system, engulfing the planets in charged particles … and in the magnetic fields they carry with them.

The sun is magnetically variable, on a roughly 11-year cycle. It’s coming out of a minimum. As the sun’s magnetic activity increases over the next few years, Earth will be hit by electromagnetic events that can potentially take down power grids; knock out spacecraft; and affect our climate.

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Alan Stahler trained as a biologist and is an amateur astronomer. He teaches private enrichment classes for students of all ages. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).


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