Author:Trevor Merrell
Course:EEE 460
Date:Spring 2002
Source: NASA/ Marshall Space Flight Center/ Science Directorate/ Solar Physics
                                                     The Discovery of Solar Flares

                                                                   
Trevor Merrell


The sun has existed since long before man began to walk on earth.  Yet there are still many secrets to be discovered and understood by mankind concerning this celestial body.  However, we know more of the sun now than was understood 400 years ago.  The sun has always been an integral part of man's existence.  With the introduction of satellites, deep space probes, and manned spacecraft, it is more important than ever to understand the effects of the sun.  One of the aspects of the sun being intensely observed, measured and studied presently is the solar flare.  Even though they may always have existed, solar flares weren't discovered until the late 19th century.

The unaided eye has always been able to see the sun but it wasn't until the telescope was invented that the sun was seen "close up".  Before this event in 1610 the effects of solar flares were observed unknown to those who witnessed them.  One example occurred in A.D. 34.  Solar flares are a direct cause of a phenomenon known in the Northern Hemisphere as aurora borealis, or "northern lights."  In A.D. 34 Tiberius Caesar mistook the glow of the northern lights on the horizon for a fire in the coastal town of Ostia.  He ordered Roman soldiers to march to the town and they found no fire. [1]

The first visual observations of solar flares themselves occurred during studies of sunspots.  Sunspots were first systematically observed by Galileo, Christopher Scheiner, and Johann Fabricius around 1610. [2] This was actually contrary to current belief.  Western religions said the Sun had no "blemishes" and Galileo "was forced to recant his observations and was placed under house arrest." [3]

Interest in sunspots did not grow until more than 200 years later.  Heinrich Schwabe of Germany was an amateur astronomer.  Over a 17 year period he would scan the sun and record it's spots.  This is when he discovered a pattern in the variations.  His findings were published in 1850 and scientists all over the world became interested in the "11-year sunspot cycle." [3]  Two of these scientists were Richard C. Carrington and Richard Hodgson. [5]

Richard Christopher Carrington was greatly influenced by Schwabe's discovery and began an intense study of the sunspots.  He even  published some of his own findings in a collection "Observation of the Spots of the Sun" in 1863. [3] On September 1, 1859 two men independently made a surprising and miraculous discover.  Carrington and Hodgson were both observing the sunspots when they became the first eye witnesses of a solar flare.  In his own words, Richard Carrington describes his observation:

...
within the area of the great north group, two patches of intensely bright and white light broke out...My first impression was that by some chance a ray of light had penetrated a hole in the screen attached to the object glass, for the brilliancy was fully equal to that of direct sun-light; but by at once interrupting the current observation, and causing the image to move...Very shortly afterwards the last trace was gone. In this lapse of five minutes, the two patches of light traversed a space of about 35,000 miles. [4]

Hodgson recorded a similar experience to that of Carrington.  Both men had seen a rare solar flare visible in white light.  Approximately 17 hours later, a magnetic storm took place and the aurora was seen as far south as Cuba.  Carrington linked the two together but cautiously stated, "one swallow does not make a summer." [3]  Perhaps he did not yet understand the importance of his discovery and the effect of solar flares here on earth.

In July of 1892, George Ellery Hale observed two large flares followed by big magnetic storms nearly a day later.  After World War II scientists began to monitor cosmic radiation using Geiger counters and other instruments. [2]  Scientists have continued to study the affects of the sun and solar flares on mankind.  The study has intensified as we continue to put more satellites into space and as we have the technology to understand the sun.

For more information on how Solar Flares effect spacecraft click here



References

1. Kiger, Patrick J. Solar Havoc - A History,
http://tlc.discovery.com/tlcpages/sunstorms/sunstorms_main.html
2. Stern, David P., Peredo, Mauricio. The Sun - History, Feb. 2000,
http://www-istp.gsfc.nasa.gov/Education/whsun.html
3. Charbonneau, Paul. General Solar Information, Mar. 2000,
http://www.hao.ucar.edu/public/education/general/general.html
4. Carrington, Richard C. "Description of a Singular Appearance seen in the sun on September 1, 1859." Monthly Notices of the Royal Astronomical Society, vol. 20, 13-15, 1860.
5. What is a Solar Flare?
http://hesperia.gsfc.nasa.gov/sftheory/