Transcript The Sun is a ball of gas!

The Sun, our favorite star!
The Sun is the basis
for all of our
knowledge of stars.
Why?
WE CAN SEE IT REALLY WELL.
Today we will take a journey to the
center of the Sun, starting with what
we can see…
…and ending up
deep in the core.
Overview of Solar Structure
Main Parts:
The Sun is made of
mostly HYDROGEN and
HELIUM
The Corona
• Outer layer of the Sun
• Millions of degrees
but very diffuse
• Extends millions of
kilometers into space
• Hot and energetic,
gives off lots of x rays!
Mass is ejected
into space as the
solar wind
• The Sun has intense magnetic fields
• The magnetic fields release energy from the Sun
• Release seen in sunspots, flares, coronal
mass ejections & other phenomena
In detail…
Flares
This twisting leads to the
loopy structures we see!
BE AMAZED!
Earth to scale.
Yes, really.
The Sun’s magnetic fields create
sunspots
The Sun has an 11-year solar cycle
Maximum
Minimum
Visible
Ultraviolet
Ultraviolet
Sunspots!
-284
-174
304nm
nm
nm
Ultraviolet
195
nm
temperature is about 5800 K…
• Remember how the temperature and
color of stars are related? The temperature
of our Sun gives it its yellowish color!
Our Sun is really
yellowish green,
but our
atmosphere
absorbs and
scatters some of
the blue light.
Where is all this energy made?
In the core.
Why and how?
The core is so hot and has such high
pressure that FUSION can take place
Why are the central pressures so high ????
Pressure
Gravity pulls the surface of the
Sun in compresing inner layers
and heating them up, but the
Sun doesn’t collapse…
What is pushing back???
The pressure of the HOT gas
layers below.
This applies to all layers of the Sun. Gravity pulls
outer layers in, Gas Pressure pushes them out.
It is pretty hot at the center!!!!
Why does high pressure in the core
lead to Fusion?
High
Temperature
and Density
allows nuclei to
interact!
Nuclei can FUSE
together:
“Nuclear Fusion”
Energy Production in Stars:
The short version.
p
p
p
n
p
p
4H
n
p
+
Energy
1He
4 1H + 2 e --> 4He + 2 neutrinos + 6 photons
4 Hydrogen Atoms fuse to make 1
Helium Atom and a bunch of energy.
How does fusion generate
energy?
The Sun is made mostly of
HYDROGEN and HELIUM
4 protons in H are
slightly more
massive than the
2 protons + 2
neutrons in He
Some mass converts
to energy!
Sunshine = Energy from Fusion
E=
Energy
2
mc
Mass
Speed of
Light
Speed of light is BIG-- so a little
mass can turn into a LOT of energy!
How many students does it take to power a
lightbulb?
Wanna know what you’re worth, energy-wise?
It’s pretty easy to figure out!
Take an average
student, of about 70kg.
E = mc2
So if we turn this whole student from mass into energy in
a single second, we get:
18
E = 6.3 x 10
J
If a typical lightbulb is 60 Watts,
the energy from a student could keep it lit for…
200 BILLION YEARS!
By comparison, the Sun shines with a luminosity of 1026 Watts.
(that’s a lot of lightbulbs)
review:
• Gravity compresses and heats the center of the sun
• At the core nuclear reactions take place
• The Sun is a giant nuclear reactor
• Energy flows from the core outward, but how
does it get out and end up as sunshine?
The next two layers of
the Sun are all about
getting the energy being
made in the core out
into space!
It takes a lot of time, but
we get it eventually.
How does energy get from one place
to another?
1.
Convection
2.
Conduction
3.
Radiation
Convection and Radiation are most
important for the Sun!
Convection
Hot stuff rises…
Cool stuff sinks!
BOILING
Conduction
Metal of the pan heats by conduction…
…heat travels through the atoms of the pan
Not very important for stars!
Radiation
•
Ionized
gas •
•
Photons can “scatter” off of unbound electrons
When they scatter, the photons share their
energy with the electrons
The electrons get hotter
How do we connect
what we see to the
Sun’s structure?
Sun’s Spectrum has
ABSORPTION LINES
Hot source makes a continuous
thermal spectrum
Light passing through a cloud
of cooler gas gets some light
absorbed out:
ABSORPTION SPECTRUM
So how does this apply to the Sun?
 Outer layers of the Sun are cooler than interior
 Interior opaque part of Sun produces a thermal
spectrum, while cooler outer layers produce absorption
lines!
Really high resolution spectrum of the Sun:
lots of absorption lines!
Compare Burning with Fusion
• 1 gallon of gas powers my beautiful red
Velostar for about 25 miles
• 1 gallon of hydrogen fusion would
power my Velostar for 140 million miles
and farther
• All the way to the Sun!
How Much Fusion a
Second?
• Einstein’s formula
– E = m c2
• The luminosity of the Sun is
– 4 x 1026 Watts
• So …
The Sun loses
4 million tons
of mass per
second!
The Sun Takes About 4
Weeks to Rotate
•What is the sun made of?
• We know diameter & mass
• Density = mass / volume
– Density = 1.4 times water!
– Low density +
– Hot temperature The Sun is a ball of gas!
• Determined from study of spectrum and
atomic spectra in the laboratory
• 74% Hydrogen
• 25% Helium
• 1% All other elements
Particles emitted by the sun detected
on the Earth confirm picture of the Sun
given in this power point. Good night.