Dr. Craig DeForest
NASA/Goddard Space Flight Center

Thursday, June 17, 1999
IfA Auditorium 3:30, Refreshments 3:15

Title

"SOLAR POLAR PLUMES:  A Key to Coronal Mysteries"

Abstract

What heats the solar corona?  What accelerates the solar wind?  These
questions -- two of the three prime scientific challenges of the SOHO
spacecraft -- have puzzled solar and stellar physicists since the
discoveries, nearly 70 and 50 years ago, that the Sun's corona is a
thousand times hotter than its surface and that the solar system is filled
with a tenuous but very rapidly moving "wind" of particles flying from the
surface of the Sun into interplanetary space.

Polar plumes appear in coronagraphs and during eclipses as luminous rays
emanating from the poles of the Sun.  They last for days or weeks, fading
in and out without fanfare and extending at least 10 times the Sun's
diameter into interplanetary space.  Because they are the most quiescent,
simple structures in the solar corona, they give us our best portrait of
the "background" processes that heat the corona as a whole.  Yet even these
"simple" structures pose intriguing puzzles that, as yet, defy complete
understanding.

I will describe recent developments in our understanding of these enigmatic
structures, presenting some of the spectacular data from SOHO and from
other spacecraft and showing how they bear on these two most basic puzzles
of solar/stellar coronal physics.