The Sun

1
The Sun

• Chromosphere, Corona, and Solar Wind

2
The Chromosphere

• The chromosphere (chroma the Greek word meaning
  color) is the second of the 3 regions of the
  suns atmosphere. Its temperature and location
  are intermediate between those of the photosphere
  and the corona.
• The pink region seen just before totality in a
  solar eclipse is the chromosphere.
• Its temperature ranges from 10,000 K to more than
  1,000,000 K.
• Prominences, seen in this picture, are clouds of
  gas that extend from the chromosphere into the
  corona.
• The pink color is mainly due to the Balmer lines
  in the hydrogen spectrum. Since we see the hot
  chromosphere against virtually empty space, this
  emission is just what is predicted by Kirchoffs
  rules.

3
Spicules

• Columns of gas from the chromosphere that rise
  into the corona.
• Up to 1,000 km in diameter and 10,000 km high.
• Cooler than the surrounding corona.
• Typically rise for about 5 minutes at 25 km/s.
• Quickly fade away.
• Form on the boundaries of supergranules.

Spicule activity on the Limb of the Sun
http//www.bbso.njit.edu
4
The Solar Corona

• Seen during a total solar eclipse or by use of a
  coronagraph.
• Includes iron, nickel, and calcium ionized up to
  15 times.
• This implies that its temperature is more than a
  million Kelvins.
• Temperature varies from 50,000 K (just above the
  chromosphere) to 3,500,000 K (in the outer
  corona).

Eclipse image from http//science.msfc.nasa.gov/
5
X-Ray Picture of the Sun

• Coronal holes are dark regions where the
  temperature and density are relatively low.
• The bright regions have relatively high densities
  and temperatures, so they emit more x-radiation
  than the coronal holes.

Coronal Holes
6
The Solar Wind

• The solar wind is a flow of particles awayfrom
  the Sun.
• They pass Earth at speeds from 400 to 500 km/s.
• This wind sometimes gusts up to 1000 km/s.
• Leaves Sun at highest speeds from coronal holes.
• Stretches magnetic field lines away from the Sun.
• When particles arrive at Earth, they are funneled
  toward the north and south poles by Earths
  magnetic field. When they hit the atmosphere,
  they cause it to glow. This produces the aurora
  borealis and the aurora australis (northern and
  southern lights).

7
Coronal Loops Magnetic Heating the of the Solar
Corona
Coronal loop arch-shaped region where plasma is
trapped by the suns magnetic field.
Click inside this box to watch a coronal loop
animation. Click outside of it to skip the video
or move on.
http//vestige.lmsal.com/TRACE/
This animation produced at Lockheed uses TRACE
(Transition Region and Coronal Explorer) images.
Near the end of the animation, a simple
theoretical model replaces the TRACE images.
Notice especially that the base of the loop is
the brightest part. This shows that heat is
generated primarily where plasma leaves the
photosphere and where it later reenters it. Most
of this heat ends up in the corona, where the
temperature can be as high as 3.5 million
Kelvins. There may be other mechanisms that
transfer heat to the corona, such as microflares
with temperatures up to 5,000,000 K. All of them
involve the interaction of solar matter with
magnetic fields.