In This Lesson:
Unit 4
The Sun
(Lesson 1 of 2)
Today is Tuesday,
May 23rd, 2017
Pre-Class:
Name something the Sun does.
That can be a thing it does in space
or a thing it does for Earth.
http://www.wired.com/wp-content/uploads/images_blogs/wiredscience/2010/10/twister768.gif
The Sun
Today’s Agenda
• “Here comes the Sun…” (do-do-doo-do)
– It’s all right…
• Solar structures
• Solar behaviors
• A multimillion dollar pseudo-failure.
• Where is this in my book?
– Chapter 11 (pages 323 – 348).
By the end of this lesson…
• You should be able to describe the path a
photon of light takes from the core of the Sun
outward to Earth or another destination.
• You should be able to identify and explain
patterns of solar behavior.
Our last unit…
• …featured comets, among planets and other
space debris.
• In reality, though, in astronomy, planets (and
humans) are not the stars of the show.
– See what I did there?
Da Sun
• Furthermore, even gravitationally, something
else is at the center of this story.
– The Sun.
• I hope you got the sense that a comet hitting
Earth would be a very, very bad thing.
• But what about a comet hitting the Sun?
– NASA Captures Giant Comet Hitting Sun
Perspective
• The usual size perspective:
– The Largest Star
• And for what will become our closure
bookend video, watch this next video closely.
– It’s years and years of data from NASA’s SDO (Solar
Dynamics Observatory).
– Take in the images – we’ll add our own narration
at the end of the lesson.
– NASA Solar Dynamics Observatory
Your Introduction
• We’re going to do a little reading from good
ol’ Discover magazine to introduce the Sun.
– I think you’ll find the Sun is a bit more involved in
your life than you might have guessed.
• Forecasting the Sun’s Weather reading
The Sun and You:
Distance Makes the Heart Grow Cooler
• The Sun has a hand in a lot:
– Light
– Warmth
– Wind
– Food
– Keeping us in the right part of the solar system…
• So it’s kinda important to us.
The Sun and You:
Distance Makes the Heart Grow Cooler
• Okay, it doesn’t literally have hands.
– Or gloves.
– Or a tongue.
– Or teeth.
•
•
•
•
Whoa. Chill out there, Sun.
Okay, okay, I’m sorry.
Hey, this doesn’t concern you, Moon.
Beat it.
http://thumbs.dreamstime.com/t/sun-moon-personified-grinning-frowning-30362467.jpg
http://www.clipartbest.com/cliparts/yio/A4n/yioA4nyiE.jpeg
https://whisperinggums.files.wordpress.com/2011/02/sunclkerocal.png?w=600
So what does the Sun have?
• Magnetism.
– The Sun is the single most magnetic object in the solar
system.
• So it has poles, like Earth, and they switch every so often, like
Earth (though in the Sun’s case it’s every 11 years).
– The magnetism is generated by granulation regions
(more later) and in part by larger features like sunspots
(more later).
• Magnetism is going to explain virtually everything
else we learn about the Sun.
– Keep that in mind. It’s the “why” for most of the lesson.
So what else does the Sun have?
• Suppose you were sent by a
criminal mastermind (some
crazy 1970s James Bond
villain or something) to a
prison located in the center
of the Sun.
– Better bring sunscreen.
• SPF 9,000,000,000 should do it.
• Through which layers of the
Sun would you pass on your
escape?
For your notebooks…
• Draw a shape like this
one, leaving room to add
labels and definitions.
– It’s 6 layers, plus one
more for the wavy stuff
outside it.
Not to scale.
Solar Layers: Core
• Your starting point is the Sun’s core.
– Like the outer planets, it’s not really a
rocky surface.
– Instead, it’s gas that has been
compressed to densities not paralleled
in any of the familiar parts of Earth.
• Because the Sun is so big, pressure
grows immensely.
– Temperatures here reach 15,000,000 K
(27,000,000 °F).
– Atomic structure is destroyed –
making plasma – and kick-starting
fusion reactions.
Plasma and Fusion Reactions
• Let’s remind ourselves of the structure of the
(typical) atom:
– Protons (+) and neutrons (0) in the nucleus.
– Electrons (-) around the nucleus.
– A single proton can also be written as H+.
• Because of the intense heat and pressure inside
the core, atoms get broken apart.
– Neutrons leave the core.
– Protons (hydrogen nuclei) get slammed together into
helium (He), generating a great deal of energy.
Plasma and Fusion Reactions
• Technically there’s a lot of quantum physics wizardry
going on in that fusion reaction I just described, with
sub-subatomic particles and antimatter like neutrinos
and positrons abounding.
– Plus, technically some of the He mass is lost as energy.
• Worry not about those, instead, just keep in mind:
– The Sun combines hydrogen atoms into helium atoms
through fusion reactions powered by intense pressure
and heat.
– The fusion process is known as the proton-proton (P-P)
chain and it generates photons (light) as byproducts.
Plasma and Fusion Reactions
http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/fusion.html
FAQ: Gamma Rays
• Q: Aren’t gamma rays dangerous? It looks like the
Sun is making a lot of them. Since they don’t get
deflected by the magnetic field of Earth, what’s
stopping them?
• A: They are dangerous and the Sun does make a lot
of them. However, they’re made in the core of the
Sun and have a long way to go to get out of the Sun
and toward Earth. In that exit process, they get
attenuated down to visible light photons. It takes
that gamma wave photon around 170,000 years to
exit the core anyway.
Sun Structure
Core
(hot, fusion reactions)
Not to scale.
Solar Layers: Radiative Zone
• Surrounding the core is the
radiative zone (also known as
the radiation zone).
– Here, atoms pass the energy gained
from the fusion reactions in the
core from one atom to another
(aka, radiation).
• Because the radiation process is
random (energy may move
outward or inward), it takes
around 170,000 years for it to
emerge from the radiation zone.
http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/randwalk.html
Understanding Radiation
• I’ll borrow an analogy from the University of
Montana:
– Imagine a crowded gym, so crowded that no one could
move very far at all, and everyone is holding a water glass.
– On one end of the gym is a water fountain; at the other
end is a thirsty person (we’ll call her Eunice).
• That person can’t move to the fountain him/herself.
– Radiation is like if someone near the sink filled a glass of
water, then poured it into his/her neighbor’s glass, who
poured it into his/her neighbor’s glass…and so on…until it
reached Eunice.
http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/Radzone.html
Understanding Radiation
• The radiative zone works the same way, except
it’s energy being passed between atoms.
– The atoms are too closely packed to move.
• The other difference?
– The energy in the Sun is passed randomly, so it may
take a very long time to get out of the radiative zone
and into the next layer.
http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/Radzone.html
Sun Structure
Radiative Zone
(heat passed between atoms)
Core
(hot, fusion reactions)
Not to scale.
Solar Layers: Convection Zone
• Surrounding the radiation zone is
the convection zone (or,
similarly, the convective zone).
– Convection, like a convection oven,
involves the movement of atoms of
high energy, not simply a passage
of energy between atoms.
• The density here is lower, so
atoms (in large groups) move up
when they have a lot of energy,
rising toward the Sun’s surface.
http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/convect.html
Sun Structure
Radiative Zone
(heat passed between atoms)
Core
(hot, fusion reactions)
Convection Zone
(matter rising/falling)
Not to scale.
Convection?
• If the idea is confusing, consider this:
– Hot air _____.
• Rises, right?
• But why does hot air rise?
– It’s not because of the temperature.
– It’s because it’s less dense.
• In the same way, warm ocean water currents
tend to be near the surface and hot gas bubbles
rise out of a pot of boiling water.
– For the Sun, that means blobs of material rising to the
surface and then sinking back down once they’ve
released energy.
Back to the analogy…
• Suppose, during your escape from your solar prison,
observers from Earth try to watch your progress.
• Unfortunately, so far they cannot see you.
– The gas density is so high, even at this point, that it blocks
conventional views.
• Thankfully, the inner parts of the Sun can still be
studied using helioseismology.
– It’s a relatively new field that looks at vibrations and
oscillations of the Sun’s inner parts to determine its
composition.
– Similarly, geoseismologists study the Earth’s composition
through earthquake vibration transmission.
Solar Zones
http://solarscience.msfc.nasa.gov/images/cutaway.jpg
Solar Layers: Photosphere
• Finally, on your journey outward,
you reach the very thin
photosphere.
– Quite literally, “ball of light.”
• This is the visible surface of the
Sun.
• Because of the convection zone
beneath it, we see regions where
material is rising and regions
where it is falling.
– The resulting pattern is called
granulation.
http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/Photosph.html
Granulation
• Each granule is a convective cell, with material
rising in the bright center but falling along the
darker, bordering lanes:
http://cdn.phys.org/newman/gfx/news/hires/3-newinsightsi.jpg
http://astrobites.com/wp-content/uploads/2012/07/kauf18_4.jpg
Other Features of the Photosphere
• Supergranules are, well, big
granules.
• Sunspots are like dark
blemishes on the surface.
– They feature lower
temperatures but higher
magnetic field strength.
– They usually come in twos.
– The dark region is the umbra,
surrounded by the penumbra.
http://solarscience.msfc.nasa.gov/images/sunspot1.jpg
Sunspots are Caused by Magnetism
Randy Russell: https://www.windows2universe.org/sun/atmosphere/sunspot_magnetism.html
Other Features of the Photosphere
• Like sunspots, faculae
are areas of strongerthan-normal magnetic
field.
• Unlike sunspots,
faculae are brighter
than the rest of the
surface of the Sun.
– They’re the small bright
splotches in that image
to the right.
http://solarscience.msfc.nasa.gov/images/faculae.jpg
Other Features of the Photosphere
• Solar flares are perhaps the most dramatic
events that occur in the photosphere.
– Think of them like a volcanic eruption on the Sun,
except instead of lava exploding out, it’s
electromagnetic radiation.
• Radiation in the form of visible light, infrared light, gamma
rays, radio waves…you name it.
– Also, the energy released is on the order of
10,000,000x that of a volcanic eruption, but still small
compared to the Sun’s total energy output.
http://hesperia.gsfc.nasa.gov/sftheory/flare.htm
Solar Flares
• In three steps, a solar flare:
– Builds up – the precursor stage.
– Is released – the impulsive stage.
– Winds down – the decay stage.
• To an observer on Earth, these appear as bright
flashes of light.
– It’s caused by reorientations in the magnetic field.
• They take between a few seconds and a few hours.
• Let’s watch…
– Fiery Looping Rain on the Sun
– Solar Flare – Magnificent Eruption
Sun Structure
Radiative Zone
(heat passed between atoms)
Core
(hot, fusion reactions)
Convection Zone
(matter rising/falling)
Photosphere
(visible surface, granulation)
Not to scale.
Pause for an Activity
• Head to Quia and open the Space Weather
Interactive quiz.
– The rest is self-explanatory.
Solar Layers: Chromosphere
• Now above the photosphere
and visible to observers on
Earth, you next move to the
chromosphere, the “sphere of
color.”
– It gets its name from the red
wavelength light emitted by H.
– Here, convection continues to
transmit energy.
http://sunflowercosmos.org/cosmology/the_sun_images/12_sun_spicules.jpg
Other Features of the Chromosphere
• Filaments are dark
“threads” made of cool
material, suspended over
the surface by
magnetism.
• Plage are bright areas
above faculae.
– Remember those? Faculae
are like bright sunspots?
http://solarscience.msfc.nasa.gov/feature2.shtml#Prominences
Filaments and Plage
http://solarscience.msfc.nasa.gov/images/H_I_6563.gif
Other Features of the Chromosphere
• When filaments extend out
past the solar limb (edge),
they’re called prominences.
– FYI, prominences are different
from solar flares in that
prominences are generally tame
and cool...and “anchored.”
Prominences
• Violent, hot prominences are
effectively solar flares, and violent
solar flares may be termed coronal
mass ejections (CMEs).
• Spicules are like little “flames”
shooting off the
chromosphere.
http://solarscience.msfc.nasa.gov/images/spicules_color.jpg
http://solarscience.msfc.nasa.gov/images/prominence.jpg
Spicules
Sun Structure
Chromosphere
(filaments, plage, spicules)
Radiation Zone
(heat passed between atoms)
Core
(hot, fusion reactions)
Convection Zone
(matter rising/falling)
Photosphere
(visible surface, granulation)
Not to scale.
Solar Layers: Transition Zone
• It’s been rather hot all through
this journey of yours, but thus far
things have actually been cooling
as you go from the inside out.
• Oddly, as you exit the
chromosphere, you notice an
uptick in temperature.
– “Uptick” as in 20,000 K in the
chromosphere to 2,000,000 K in the
corona.
• The region of sharp temperature
change is the transition zone.
Transition Zone
http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/transreg.html
Sun Structure
Chromosphere
(filaments, plage, spicules)
Radiative Zone
(heat passed between atoms)
Core
(hot, fusion reactions)
Convection Zone
(matter rising/falling)
Photosphere
(visible surface, granulation)
Not to scale.
Transition Zone
(increase in temperature)
Solar Layers: Corona
• On the last part of your escape,
you’d enter the corona.
– The Sun’s outer atmosphere and
hottest point (not including the
core) – over 1,000,000 °C.
– It’s what becomes visible during a
solar eclipse.
– Solar flares reach from the
photosphere all the way out to the
corona when they erupt.
– Separately, the corona is responsible
for the solar wind.
http://solar.physics.montana.edu/ypop/Spotlight/SunInfo/helmet.html
The Corona
http://i.telegraph.co.uk/multimedia/archive/01594/corona-large_1594047a.jpg
Other Features of the Corona
• Helmet streamers are peaks in
the corona above sunspots,
prominences, or filaments.
• Polar plumes are “streamers”
from the corona at the poles of
the Sun.
• Coronal mass ejection (CME) is
the general term for a violent
outgassing of the corona.
http://solarscience.msfc.nasa.gov/images/eit020.jpg
http://solarscience.msfc.nasa.gov/images/helmet_streamer.jpg
Helmet Streamers
Polar Plumes
Other Features of the Corona
• Coronal loops are, well, loops of
corona.
– They may be associated with
flares; they may not.
– Coronal Loops video
• Coronal holes…figure it out.
– They’re often found at the poles.
– Even though they’re dark, they
seem to be the source of the
fastest parts of the solar wind.
http://solarscience.msfc.nasa.gov/images/Yohkoh_920508.jpg
Coronal Loop
Coronal Hole
Corona
Sun Structure
(visible during eclipses)
Chromosphere
(visible surface, granulation)
Radiative Zone
(heat passed between atoms)
Core
(hot, fusion reactions)
Convection Zone
(matter rising/falling)
Photosphere
(visible surface, granulation)
Not to scale.
Transition Zone
(increase in temperature)
Solar Structures Visual Review
• To the computers!
What is the Solar Wind?
• The solar wind, as we’ve seen, is a constant
stream of radiation from the Sun.
• In fact, it’s perhaps best thought of as a very
thin gas sent through space.
• To learn more about it, NASA launched the
Genesis spacecraft in 2001, designed to collect
(yes, collect) some of the solar wind and
return it to Earth.
Genesis
• In September 2004, Genesis was due back to Earth.
• On its way through the atmosphere, the craft’s
deceleration sensor never worked (it was installed
backwards).
• The parachute never deployed, sending the return
capsule crashing into the desert in Utah.
• Thankfully, NASA scientists were able to recover some
of the samples collected and still learned something
about the nature of the solar wind.
– Mainly about the composition of the solar wind and its
effects on materials, since they still managed to get a pure
sample.
Sun Structure Summary Slide
#theletterS
•
•
•
•
Core
Radiation Zone
Convective Zone
Photosphere
– Sunspots, faculae, granules, supergranules, solar flares.
• Chromosphere
– Spicules, prominences, plage, filaments.
• Transition Zone
• Corona
– Helmet streamers, polar plumes, coronal loops/holes.
Sunspot Cycles
• What Patterns are Revealed by Sunspots? activity
– Turn this thing in as individuals, but you may work with
a partner.
• So you both need computers.
– Make sure your graph features your name.
– Then, use the graph to answer the questions on the
same-named Quia “quiz.”
• The printer of choice is C321A 1.
• Put the directions copy (if you have one) and your
graph in the Turn-In Box.
Other Features of the Sun: Cycles
• The sunspot cycle is 11 years on average.
– Sunspots seem to occur in waves, with many happening
at once and then, at other times, only a few.
• The solar cycle is 22 years on average, and features
the flipping of the North and South magnetic poles
twice (returning to the original N-S orientation after
the full cycle has completed once).
– Solar Cycle video
The Maunder Minimum
• Here’s something interesting.
• In the second half of the 17th century, global
temperatures were lower than normal.
– So low, in fact, that the time period became known
as the “Little Ice Age.”
• What may have played a role here? The solar
cycle.
– During the same time period as the Little Ice Age,
sunspots dramatically decreased in number…and
stayed low.
The Maunder Minimum
• Today, we know the period as being part of the
Maunder minimum, after a late 19th century British
astronomer.
http://www.odlt.org/dcd/images/maunder_minimum.gif
“Oooh, climate change!”
• Nope, sorry.
• While sunspots may affect Earth’s climate,
there’s really no link with the recent pattern in
rising temperatures.
– In other words, temperatures have been
consistently rising across Earth over the last forty
years but solar cycles keep going up and down.
• It’s still humans. 
• Need numbers?
Sun ≠ Climate Change
https://skepticalscience.com/solar-activity-sunspots-global-warming.htm
Sun ≠ Climate Change
El Niño/Southern Oscillation
(ENSO)
https://skepticalscience.com/solar-activity-sunspots-global-warming.htm
Other Features of the Sun: Rotation
• The Sun rotates once
every 27 days.
– It’s averaged to 27
since the Sun is all gas
and different parts
rotate at different
rates.
• The equator rotates
once every 24 days,
but the poles take
around 30 days.
The Future of the Sun
• Let’s return to the core of the Sun for a moment.
– “No! I can’t go back there, no!”
• We talked about how the Sun fuses hydrogen atoms
into helium atoms.
• How much hydrogen does it have?
– The Sun is about 71% H and 27% He, with heavier metals
and non-metals making up the remaining 2%.
• That hydrogen fuel is due to run out in 5-7 billion
years, but in the meantime, it’ll be getting warmer.
• And that’s one of the topics for our next lesson: stars
and their life cycles.
Solar Observations
• Let’s go outside and (safely) stare at the Sun.
• An important note:
– We’re using a telescope with a specially-designed solar
filter that blocks the vast majority of the Sun’s light and
radiation.
• Seriously, it’s rated to block 99.999% of sunlight.
– Using the scope to observe the Sun directly without the
filter would cause immediate and irreversible damage to
your eyes.
• Using an eyepiece with a filter is also a bad idea.
– They tend to break and eyes tend to be damaged.
• In other words, don’t do this without adequate
preparation and without knowledge of the risks.
Closure
• NASA Solar Dynamics Observatory video
(again)
• UniverseToday – How Many Ways Can the Sun
Kill You