THE SUN:
AWESOME AND ACTIVE
Boston University PHOTON
Outreach Presentation
The Sun
• An average-size yellow star,
just like billions of others in
the universe
• Center of the solar system,
Earth orbits around it
• Formed about 4.6 billion
years ago
• The sun has a mass of
2x1030 kg or 330,000
Earths, that’s 99.8% of the
mass in the solar system.
The Sun’s Energy & Earth
• The Sun is the source of all of the
energy on Earth.
• The amount of energy that reaches
Earth from the Sun in one second is
enough energy to meet
Massachusetts’ current energy needs
for 32,655,294 years!!!*
• About half the energy that hits the
Earth is absorbed and used to heat
the planet.
• You can feel this energy in the form
of heat on your skin on a sunny day.
*figure based on data from California Energy Commision:
http://www.energy.ca.gov/electricity/us_percapita_electricity_2003.html
Where does the Sun’s Energy Come From?
• Energy is produced in the Sun’s core through a process known as nuclear fusion.
• Nuclear fusion is when nuclei of one kind of element combine to make a new nucleus in
that requires less energy to hold it together. This difference in energy is spit out as a result
of the reaction.
• The Sun’s nuclear fusion occurs when four hydrogen nuclei combine to make helium and
release energy.
• This type of reaction can’t happen just anywhere, it can only happen at incredibly high
temperatures and pressures like those found in stars, somewhere around 23 million
degrees!!
+
1 Helium nucleus
4 Hydrogen nuclei
Energy
How much energy does the Sun
make?
• We know how much energy the
Sun emits by measuring the
amount of energy that reaches
Earth.
•
The Sun consumes 660 million
tons of hydrogen releasing 100
billion megatons of energy per
second! That’s the same energy
as 20 billion Hydrogen bombs
every second!
•
Based on the amount of
hydrogen the Sun consumes per
second and the mass of the Sun,
we estimate its lifetime to be 50
billion years.
Nuclear Fusion Hydrogen Bomb—50
megatons
What’s inside the sun?
Layers of the Sun
1. Core
the core of the sun alone is the
size of 13 Earths!
2. Radiative Zone
energy from the core radiates
through this part of the Sun
3. Convective Layer
convection cells move energy
through this part of the Sun
4. Photosphere
This is the part of the sun we see
5. Chromosphere
a part of the Sun’s atmosphere
6. Corona
Diameter of the Sun = Diameter of 56 Earths!
This is a bright halo around the
Sun
Energy Escapes the Sun
• Fusion occurs in the Sun’s core,
the hottest part.
• The energy released by the fusion
in the Sun’s core is in the form of
light.
• It only takes 8 minutes for light
from the surface of the Sun to
reach Earth
• But it takes 170,000 for the light
energy from the core to reach the
Sun’s surface because it doesn’t
go in a straight line
The Changing Sun
• The surface of the Sun is
constantly changing
• The Sun is shooting particles
off it all the time called the
Solar Wind
• There is an 11-year “Solar
Cycle” when the Sun goes
from being very active (solar
maximum) to not not very
active (solar minimum
How is the Sun active?
• The solar cycle is
characterized by the
rising and falling of solar
activity
• The solar maximum is
the period of greatest
solar activity
• During solar maximum
the Sun is more active
meaning there are more
sunspots and solar flares
Sunspots
• What?
– ‘Dark’ spots on the
Sun's surface that are
cooler than the
surrounding areas
– Temperature of:
Sunspot= 3800 K
Surrounding area=
5800 K
• Why?
– The strong magnetic
field in that area stops
the area from being
able to transfer energy
so the temperature
isn’t as high
More about Sunspots
– Sunspots can be about the size of Earth or even
bigger!!!
– They come in pairs
– They are still really hot, just not as hot as the rest of
the Sun’s surface
– Sunspots move across Sun’s surface as it rotates
Magnetic Activity on the Sun
• Sunspots are caused by
strong magnetic fields
• Magnetic “ropes” break
through the Sun’s surface
• At each end of the rope
is a sunspot
• It is the Sun’s magnetic
activity that causes solar
storms and solar flares
How do we know all of this about the
Sun?
• Telescopes
– You can look at the Sun through a telescope with special filters.
– You can also use a solar telescope that projects the image of the Sun
onto a piece of paper instead of into your eye.
• Satellites
– There are also several spacecraft that
are observing the Sun: SOHO, TRACE, STEREO
– These satellites look at the Sun in all
different kinds of light (ultraviolet, visible,
infrared, X-ray) to see everything that is
going on
– Many cameras on telescopes need to use
a caronagraph, where a disk is used to block
out the Sun’s surface so we can see all the dim
stuff that the Sun’s brightness would drown out