The Solar Corona: Arthur B. C. Walker

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The Solar Corona Arthur B. C. Walker prepared
by Ruth Howes Marquette University with
support from the Wisconsin Space Grant Consortium
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Why Study the Sun? The Sun is a very typical
main sequence star that is close to us. The
Sun influences climate on Earth, Radiation from
the Sun released during violent solar events
can pose a hazard to both people and
electronics in space as well as disrupt radio
communications.
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The photosphere is the visible surface of the
Sun. The Suns atmosphere lies above the
photosphere and has 2 layers. The chromosphere
lies just above the photosphere thickness
10,000 km temperature rises from 4500K at
the photosphere to 50,000K The
corona lies above the chromosphere. thickness
greater than 1,000,000 km and variable
temperature 1-3 million K in variable
pattern density 10-12 of photosphere so not
much heat and little radiation. Visible
only during solar eclipse.
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Layers of the Sun downloaded from
http//imagine.gsfc.nasa.gov/docs/science/know_l1
/sun.html
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Studying the Corona Emission in short wavelength
UV and X-ray regions Bright photosphere swamps
dim corona coronograph produces artificial
eclipse Atmosphere blocks short wavelength
UV Conventional lenses cannot focus UV or X-ray
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The solar corona as seen during a total eclipse
downloaded from http//imagine.gsfc.nasa.gov/docs
/science/mysteries_l1/corona.html
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The Corona in Ultraviolet Light showing a coronal
hole over the pole and several flares Image
downloaded from http//solarscience.msfc.nasa.gov/
index.html
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Image from NASA and downloaded from
http//en.wikipedia.org/wiki/ImageAtmospheric_tra
nsmittance_infrared.gif
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Arthur Bertram Cuthbert Walker Discovered
science as a child. Attended Bronx High School
of Science Received bachelors degree from Case
Institute of Technology Ph.D. in photomeson
production from the University of
Illinois Served at the Air Force Weapons
Laboratory and discovered space-based
instruments In 1965, joined Space Physics
Laboratory of Aerospace Corporation Recruited
to Stanford University in 1974 as a professor
of applied physics and worked there for 31 years
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Arthur B. C. Walker image from http//news-servi
ce.stanford.edu/news/2005/may18/memlwalk-051805.ht
ml
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• Walkers development of ultraviolet telescopes
• Special materials developed that were created
  with
• very uniform planes of atoms that behaved
  like
• atomic planes
• Materials made of different substances can be
  tailored
• to reflect different wavelengths by
  varying the
• spacing between planes.
• A parabolic mirror coated with such a material
  will focus
• normally incident ultraviolet or x-rays
  to form an image.
• 4) Satellites carried several telescopes tuned to
  different
• wavelengths

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When d is equal to ?/2, the waves will interfere
constructively. That wavelength of radiation
will reflect.
EMR of Wavelength ? incident as a parallel
wavefront perpendicular to the atomic planes.
Atomic plane spaced d apart
Materials with tailored layers of atoms can
maintain d needed To reflect ultraviolet and
x-ray wavelengths.
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(No Transcript)
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Getting ready to launch the Multi-Spectral
Solar Telescope Array Image downloaded
from http//solarscience.msfc.nasa.gov/MSSTA.shtml
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Solar image taken by the Multi-Spectral Solar
Telescope Array in the UV corresponding to a
temperature of 2 million K http//solarscience.msf
c.nasa.gov/MSSTA.shtml
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• Three Big Questions about the Sun
• (Marshall Space Flight Center)
• How does the corona get heated and maintain its
  heat?
• How can we predict when solar flares and the
  coronal mass
• ejections that accompany them will occur?
• 3. How can we predict the behavior of the sunspot
  cycle?
• Seeking answers is the STEREO Project that uses
  some
• of the technology Walker developed.

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One of the STEREO satellites under construction.
Image from http//stereo.jhuapl.edu/
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The Solar Terrestrial Relations Observatory
(STEREO) STEREO consists of two satellites which
will be placed into solar orbit. One
satellite will orbit 45o ahead of Earth. The
other will orbit 45o behind the
Earth. Instruments on the two satellites can
form 3-dimensional images of the Sun. Each
satellite will carry a suite of four
instruments. The missions goal is to understand
and predict the behavior of the Sun,
its magnetic field and its atmosphere
as it goes through a sunspot cycle.
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Coronal loops in image by MSSTA downloaded
from http//solarscience.msfc.nasa.gov/images/eit0
20.jpg
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Sun Earth Connection Coronal and Heliospheric
Investigation (SECCHI) Five telescopes
that use Walkers technique will image the
solar atmosphere and its features in three
dimensions.
In-situ Measurements of Particles and CME
transients (IMPACT) Will examine
the energies and behaviors of electrons and
ions emitted during a flare or CME and form
images based on these particles as well as
watch their interaction with the
interplanetary medium.
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The Plasma SupraThermal Ion Composition
Investigation
(PLASTIC) Study the distribution of different
types of ion from hydrogen to iron and
how their distribution changes during
CMEs and flares
STERO/WAVES Radio telescopes will monitor the
interaction of the material ejected from the Sun
with the interplanetary medium.
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MSSTA image of a solar flare Image from
http//solarscience.msfc.nasa.gov/images/flare.jpg

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Walkers work set the stage for STEREO. He also
mentored 13 Ph.D. students including the first
U.S. woman astronaut, Sally Ride. He constantly
fought for more admission of more minorities
and women to graduate programs in physics and
astronomy. He formed a group of African
American faculty at Stanford that supported
young faculty including political
scientist Condoleezza Rice.