Solar Activity and You!

The Sun, our nearest star, provides us with warmth and light. Until Galileo invented the telescope, it was once thought to be a perfect orb, free of blemishes, eternal and changeless. Sunspots are the most well known hints that the Sun's surface is constantly changing. Larger than the Earth, and with 10,000 times more intensity than the Earth's magnetic field, these are the breeding grounds for some of the most violent storms in the solar system! The number of sunspots comes in cycles lasting from 6 to 11 years; the Sunspot Cycle. With modern technology and space satellites, this solar activity cycle can now be detected in the ebb and flow of other phenomena on the Sun and on the Earth. Among the most enigmatic storms are the solar flares can erupt near sunspots. In a matter of 20 minutes, magnetic fields can heat gases to tens of thousands of degrees and release more energy than a thousand atomic bombs. Some of this gas can be hurled out from the Sun at millions of miles per hour in what are called coronal mass ejections. Both solar flares and coronal mass ejections can be very disruptive to human activity on earth and in space.

The Solar Wind

The outer atmosphere of the Sun, the corona, is familiar to many people who have watched total eclipses of the sun. But extending billions of miles further out into space is the solar wind. Like invisible roadways spanning the solar system, the magnetic field from the Sun spirals out from the solar surface. Matter ejected from the Sun flows radially outwards from the solar surface. From the time a solar storm is seen on the Sun, it can take 2-3 days for the gas to travel to the orbit of the Earth, and if the Earth happens to be in the wrong place at the wrong time, it will be hit by a million-mile wall of high temperature plasma and magnetic fields.

The Earth's Magnetic Field

Anyone can tell you that a compass points 'north' because the Earth has a magnetic field, but until the advent of the Space Age, no one really understood what this field really looked like or was capable of doing. Since Gilbert proposed in the 17th century that the Earth was a giant magnet, scientists have wondered just how this field is shaped, and how it has changed with time. The geomagnetic field which gives us our familiar compass bearings, also extends thousands of kilometers out into space in a region called the magnetosphere. On the Sun-side, it forms a protective boundary called the bow shock. Stretching millions of miles in the opposite direction behind the Earth is the magnetotail. The solar wind blows upon the magnetosphere and gives it a wind-swept shape, but when
solar storms and solar wind streams reach the Earth, the magnetosphere reacts violently. On the side nearest the impact, the magnetosphere compresses like a balloon, leaving communications satellites exposed. On the opposite side, it is stretched out, past the orbit of the Moon, or Mars and even Jupiter! The geomagnetic field is remarkably stiff, and so most of the solar wind is deflected or just slips by without notice. But some of the matter leaks in and takes up residence in donut-shaped clouds of trapped particles, or can penetrate to the atmosphere to produce the Northern Lights.

The Northern Lights

For thousands of years, humans have been treated to spectacle of glowing clouds above the northern horizon at night. Reports of these mysterious 'northern lights' abound in the oral histories of northern peoples. On rare occasions, even ancient Greek and Chinese texts mention them. It wasn't until 1896 that the Norweigan physicist Kristian Birkeland deduced that flows of electrons from the Sun were channeled into the polar regions by the geomagnetic field, and upon colliding with the outer atmosphere, would stimulate oxygen and nitrogen atoms to cast their ghostly and inspiring curtains of light.

The Aurora Borealis (near the north pole), and the Aurora Australis (near the south pole) as they are more formally called, are seen most often in a band located at a latitude of 65 degrees, and about 10 - 15 degrees wide in latitude. From space, the auroral zone looks like a ghostly, glowing donut of light hovering over the north and south poles. This auroral oval can easily be seen in satellite images, and its brightness and size changes with the level of solar activity. Aurora come in many shapes and colors depending on what is happening to the geomagnetic field and the flows of charged particles and plasmas trapped in this field. Magnetic sub-storms happen when the geomagnetic field is suddenly changed because of small changes in the magnetic polarity

of the solar wind as it passes the Earth. Typically, magnetic sub-storm aurora, also called auroral sub-storms, last only a few hours. They begin in the evening as arcs of colored light which slowly change into rayed-arcs and the familiar folded ribbons or bands. Expanding over the whole sky, the folded bands are colorful, with green rays and red lower borders which change from minute to minute and move rapidly across the sky like some phantasmagoric serpent. After an hour, the auroral shapes become more diffuse and less distinct. Geomagnetic storms are more severe than magnetic sub-storms and are caused by major changes in the direction and density of the solar wind as it reaches the Earth. It is these events that are the most remembered historically as 'Great Aurora' or as the most disruptive to radio communications. The entire geomagnetic storm can last for many days as the particles and fields around the Earth continue to readjust themselves to the passing and ebbing solar wind.

They begin with an ejection of mass by the Sun, and the impact of this plasma on the magnetosphere. Fast-moving coronal mass ejections produce shock waves in the solar wind, and this compression intensifies the density of particles impacting the magnetosphere. As the solar wind shock passes across the magnetosphere and magnetotail, magnetic fields re-orient and reconnect, releasing enormous amounts of energy and accelerating trapped particles to high speeds. These charged particles then travel down the geomagnetic field in huge currents, which cause bright and long lasting auroral displays.

Human Activities

Solar storms and the geomagnetic storms they produce in the Earth's environment, have been known for decades to be responsible for many harmful effects upon human technology on the ground and in space. Solar storms and their geomagnetic effects are known to do far more than just paint the sky with pretty colors!

The multi-billion dollar 'Global Positioning System' consists of a constellation of over a dozen navigation satellites orbiting within the Van Allen radiation belts. These satellites let humans find their position anywhere on Earth using a hand-held receiver no bigger than a pocket calculator. During solar storms, these positions are quite a bit less accurate than under calm conditions, which impacts the navigation of ships at sea and jets in the air.

Geomagnetic storms have disabled multi-million dollar communication and navigation satellites such as Anik-A, Molynia, Marecs-A and have been implicated in many electrical problems experienced by other satellites. Solar storms were responsible for Skylab burning up in the atmosphere, and for altering the orbits of other satellites and even the Space Shuttle itself. A storm on March 13, 1989 knocked out the Quebec-Hydro power system, plunging 6 million people into darkness for 9 hours.

Geomagnetic storms cause the magnetic field near the Earth's surface to change rapidly in just a matters of minutes or hours. These changes cause electrical currents to flow in long power transmission lines, telephone wires, and even in pipelines which makes the pipes corrode. On June 5, 1991 a natural gas pipeline in Russia was weakened by corrosion and began to leak its deadly, flammable cargo. A passenger train loaded with 1,200 people ignited the liquified gas and caused an explosion equal to 10,000 tons of TNT. Over 500 people were killed, and 700 more were badly injured.

Would You Believe...

Auroras can never get closer to the ground than about 60 kilometers

A sunspot has a temperature of nearly 4000 C, and would be brighter than the Full Moon if placed in the night sky.

Sunspots are often several times larger than the entire earth

The Sun rotates once every 25 days at the equator, but take up to 36 days to rotate once around at the poles.

The corona of the Sun is over 5 million degrees hotter than the surface of the Sun

The total power produced by an auroral event can exceed 1 million megawatts and produce voltages over 100,000 volts in the upper atmosphere.

Aurora are produced where the atmosphere has the same density as the vacuum inside a light bulb

Some aurora occur at altitudes of over 1000 kilometers above the Earth's surface.

The Earth's magnetic north pole is actually a magnetic south pole because the north end of a bar magnet is attracted to it.

The north and south magnetic poles are not on exactly opposite sides of the Earth.

Lightning storms can eject particles into space at nearly the speed of light which are seen as 'sprites' on the top side of a thundercloud.

A single lightning storm can be heard on the other side of the earth because some of its energy travels along local magnetic field lines which connect pairs of points on the surface of the Earth which can be thousands of kilometers apart.

Return to the: Workbook table of contents page.