A SUNNY DAY
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
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.
Return to index.
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.