1. Astronomy notes for Phys/Geog 182
Week 5 – Earth, sky, Sun, and Moon
Week 6 – Motion in the Solar System
Week 6/7 – How stars (& the Sun) work
Week 7 – The cosmos in the large
We will use a combination of simulations and worksheets
Topics align with teaching standards

2. The recommended textbook is “Astronomy”, by A. Fraknoi, D
The recommended textbook is “Astronomy”, by A. Fraknoi, D. Morrison, and S.C. Wolff Available free online at openstax.org

3. Openstax Astronomy Week 6 readings: For Monday class:
Read sections 3.1 – pp
For Wednesday:
Read section pp
Study Ch pp
For Friday:
Read Ch. 18 (skim) pp
Look at key terms and chapter summaries, but skip the
calculations in the boxed sections.

4. The Sun The closest star

5. Vital Statistics of the Sun
Diameter is about 109 Earth diameters.
Mass is about 333,000 times Earth’s mass.
Surface temperature is about 5800 K (or 5500oC).
Rotation period is about 25 days at the equator and 35 days at the poles (differential rotation). The core rotates once each week (this is new information!).
Average density is about 1.4 times that of water.
All the Sun’s energy is produced by fusion in a dense core that is at about 15.5 million Kelvin (or Celsius).
The energy travels outward through various zones.

6. Solar Prominence – photo by SOHO spacecraft
from the
Astronomy
Picture of
the Day site
link

7. SOHO (before launch, at ESA facility) (without solar panels)
Other spacecraft
looking at the Sun:
STEREO (2 of these)
SDO
and others

8. Solar and Heliospheric Observatory (SOHO) (link) is in orbit around the sun near the L1 point

9. The closest star - The Sun

10. The Sun is a layered structure

11. The atmosphere of the Sun
The outer layers are
all parts of the Sun’s
atmosphere:
Corona
Transition zone
Chromosphere
The Photosphere is the
“surface” of the Sun; it
emits the light that we see.
The Convection and Radiation Zones are named for
how energy is transported in the interior of the Sun.

12. Solar Granulation in the photosphere can be seen in movies taken by the SOHO cameras
This granulation shows
that convection is
occurring under the
surface of the Sun. On
average these granules
are about the size of a
large state like Texas
(up to 1000 miles across).

13. Above the granular photosphere is the chromosphere.

14. Next are the transition zone and the Solar Corona

15. The Solar Corona is most obvious during a total solar eclipse.

16. Coronal Hole, seen in X-ray images by Yohkoh. (link)

17. Solar Atmospheric Temperature
So much energy is flowing
through this region and
the density is so low that
the temperature of these
regions is very high.
All of this energy causes
gas to “boil” off into space,
or causes gas to be
“pushed” off the surface
of the Sun. This gas is
called the Solar Wind.

18. Solar Spectrum in the visible region

19. Solar Spectrum
This absorption spectra
tells us what elements
are in the Sun’s
chromosphere and most
likely in the rest of the
Sun, except in the core.
Likewise, spectra of stars
tells us about their contents.

21. The “active Sun” refers to times when there are lots of sunspots and the surface of the Sun is very active in other ways.
Many Prominences, Flares,
and Coronal Mass Ejections
can be seen.
Also during this time the corona becomes larger and more irregularly shaped

22. Solar Prominences are huge outbursts of hot gases that blow out into space, then often the gas cools and falls back into the Sun.

23. are loops of hot gas that rise from the surface of the sun. They are
Solar Prominences
Solar Prominences
are loops of hot gas that
rise from the surface
of the sun. They are
shaped by the magnetic
fields of the Sun.
SOHO website:
For Mar. 28, 2014, there is a movie of 8 CMEs in five days:

24. Solar Flares are much more rapid than prominences.

25. A Solar flare
on Nov. 11,
2003.
SOHO
obtained
numerous
images of
the active
Sun in
fall 2003.

26. Coronal Mass Ejection
Coronal Mass Ejection events (CME) is when an eruption on
the surface of the Sun ejects large amounts of gas into space.
These events are larger than solar flares and are less frequent.

27. The thermonuclear core produces energy by nuclear reactions which are caused by the high temperature, hence “thermo-nuclear”. (more on this later)
Much of the energy comes out of the core in the form of X-rays or gamma rays, which travel without being absorbed through the radiative zone, which is transparent to these X-rays or gamma rays (g rays).
The X-rays are then absorbed in the convective zone, and this heats the plasma in that zone, which undergoes convection, a motion which is similar to convection in any hot fluid.
The convective zone has very large convection cells, and then above that zone is the photosphere, which has smaller convection cells.

28. FIGURE 10-21 The Solar Model
(a) Thermonuclear reactions occur in
the Sun’s core, which extends to a
distance of 0.25 solar radius from the center. In this model,
energy from the core radiates outward to a distance of 0.8
solar radius. Convection is responsible for energy transport
in the Sun’s outer layers. (b) The Sun’s internal structure is
displayed here with graphs that show how the luminosity,
mass, temperature, and density vary with the distance from
the Sun’s center. A solar radius (the distance from the Sun’s
center to the photosphere) equals 696,000 km. (c) Ten most
common elements in the Sun, by the numbers of atoms of
each and by the percentage of the Sun’s total mass they
each comprise. (a: NASA)