Our Sun
is a Star
The Sun
• Is a star
• Made of gases
• Is our primary
source of
energy
70% hydrogen and 28%
helium
Light (radiation)
Image at
How Big is the Sun?
About 110
times wider
than Earth
Or
1.3 million
times bigger
than Earth
How does our Sun compare to other Stars?
• Active stars range in
size from supergiants
to dwarfs
• Stars range from very
bright (supergiants)
to very dim (dwarfs)
• Stars range from very
hot blue on the
outside (O class) to
cool red on the
outside (M class)
Our Sun is
in-between--yellow
Our Sun is a dwarf—
medium mass
So is our Sun an average star?
• No—most stars are smaller and cooler than our Sun BUT
Rotation
At the
equator
, the Sun
rotates once every
25.4 days
Near its
poles
, the Sun
rotates once every
36
days
Known as “
differential
rotation
”
Inside the Sun
• Core
• Radiative Zone
• Convection
zone
The Core
• The very inside
• temperature - 15 600 000° K
• atoms are constantly colliding
fusion
of hydrogen
The Radiative Zone
• Layer surrounding the core
• 7 million° K
• Photons made in the core bounce off of each
other as they make their way through the
radiation zone
The Convection Zone
• about 2 million K
• Because this layer is so much cooler, the hot
gases coming from the inner layers are caused to
grow in size and ascend to the top of the
convection zone.
• As gases are rising, their temperature starts to
drop, causing them to lower
Photosphere
• about 5800 K
• This is where the Sun’s light
is emitted from
• Only layer of the Sun that can be seen by
us on Earth.
Chromosphere
• Slim layer above the
photosphere
• Can only be viewed during a
solar eclipse, when the moon
blocks out the photosphere
The Corona
• The area around the sun
• Extends to over one million km
from the surface
• Temperature can reach up to 2 million K
• Emits X-ray radiation
Energy from the Sun
• Nuclear chain reaction
• Hydrogen forming Helium =
FUSION
• Releases radiation (gamma rays) =
ENERGY
!!
• The
gamma ray
loses energy as it bounces
around inside the Sun
• It is finally released at the photosphere,
primarily as visible light
Features in the
Photosphere
Sunspots
– Dark and small (but brighter than Full Moon
and big as Earth)
– Cool-- temperatures only 6,200 ° F (Sun’s
surface is 10,000° F)
– Associated with magnetic fields: one set of
spots is positive, other is negative
Image at
More on Sunspots
Solar Events
•
Flares
(Explosions of energy on the
surface of the Sun)
Solar Events - Prominences
Prominences
–
dense cloud of incandescent ionized gas projecting
from the Sun’s chromosphere into the corona.
Can extend hundreds of thousands of kilometres
above the Sun’s chromosphere.
Solar Wind
• Blows charged particles and magnetic fields away from the Sun
• Charged particles captured by Earth’s magnetic field
• Create
Auroras
or Northern and Southern Lights
Auroras
•
Electrons from solar wind are captured by the Earth’s magnetic field
• Interact with atoms in our atmosphere: oxygen and nitrogen make red and
green; nitrogen can also make violet
• Northern lights are
Aurora Borealis
, while southern are
Aurora Australis
https://www.youtube.com/watch?v=7Mz2laHjVoQ
Coronal Mass Ejection
The eruption of a huge bubble of hot gas from the Sun
This series of images of coronal mass ejections taken with
LASCO C3 (May 1-31, 1997) at
Coronal Mass Ejection’s
Effects on Earth
• Can damage satellites
• Very dangerous to astronauts
• Power problems
*** Animation of a CME leaving the Sun,
slamming into our magnetosphere.
Radiation
• Our Sun (and all active stars) emits radiation
– Radio, infrared, visible, ultraviolet, x-ray and even
some gamma rays
– Most of the sunlight is yellow-green visible light or
close to it
The Sun at X-ray wavelengths
Image and info at
http://imagine.gsfc.nasa.gov/docs/teachers/gammaraybursts/imagine/page18.html and http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/sun.html
Sun’s Radiation at Earth
• The Earth’s
atmosphere
filters out some frequencies
– Ozone layer protects us from some ultra-violet, and most
x-rays and gamma x-rays
– Water and oxygen absorb some radio waves
– Water vapor, carbon dioxide, and ozone absorbs some
infrared
Electromagnetic spectrum
http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/what_is_ir.html
Sun as a Source of Energy
• Light from the Sun is absorbed by the Earth, unevenly to:
– drive wind bands – which drive surface currents
– drive deep ocean currents
– drive water cycle
– drive weather
NASA image at http://visibleearth.nasa.gov/view_rec.php?id=107 Credit: NASA GSFC Water and Energy Cycle
Sun as a Source of Energy
• Plants need light for photosynthesis
• Without heat from the sun, the only
inhabitable areas on Earth would be near
volcanic vents
Images from http://nasadaacs.eos.nasa.gov/articles/2005/2005_rainforest.html and
Our Sun is a Regular/ Small Star
In a few Billion years… Red Giant
Supernova—Massive Star Explodes
Images at
http://hubblesite.org/newscenter/archive/releases/star/supernova/2004/09/results/50/
Hertzsprung-Russell Diagram
Our Sun – Main Sequence Star
Stars are on the Main Sequence if they are in their
Chemical Composition
• Most stars are made of
– 73% Hydrogen
– 25% Helium
– 2% Other elements
• Astronomers use spectrographs to determine elements
found in stars
Brightness of Stars
• The brightness of a star depends upon both
its size and temperature
• How bright a star looks from Earth depends
on both its distance from Earth and how
Why do stars twinkle?
• The scientific name for the twinkling of
stars is stellar scintillation
• Stars twinkle when we see them from the Earth's
surface because we are viewing them through thick
layers of turbulent (moving) air in the Earth's
Measuring Distances to Stars
• Astronomers use a unit called the
light year
to measure
distances
between the stars
• Light travels at a speed of 300,000 km/s
•
Light year
-
distance
that light travels in 1 year = 9.5 trillion
km
