Hi Rebecca.

It depends what you mean by long! If you mean long, as in long time, then the answer would be many hours, but I don't think people keep track of that.

What we do try to keep track of is the flare that produces the most energy. It is a little hard to do because the brightest flares are too bright for our instruments to observe correctly! There was one which was especially bright on November of 2003. A large flare releases something like 10 million times the energy in a big volcanic explosion.

Here is the list of the brightest flares we have observed since we started measuring them from space:

http://www.spaceweather.c...lares/topflares.html

"X" flares are the brightes tkind and the higher the number after the X the brighter the flare.

Here is some stories related to the Nov. 4, 2003 flare:

http://sohowww.nascom.nas...hotshots/2003_11_04/

http://science.nasa.gov/s.../2003/12nov_haywire/

Some stars other than our Sun produce even brighter flares. See this story:

http://www.nasa.gov/cente.../pipsqueak_star.html

Hi Rebecca,

The first flare to be seen with a telescope, was in 1859. Richard Carrington and Richard Hodgson independently observed a "white-light" flare on September 1, 1859. This flare is now referred to as a "super-flare", but it dimmed very quickly in white light. You might find it interesting to read Carrington's description of this event: http://articles.adsabs.ha...20//0000013.000.html

Sun-Earth Day 2009 also has an interesting discussion of flares:

http://sunearthday.gsfc.n...tellarexplosions.php