Download 8.2 Solar Nebula Theory and the Sun

Solar Nebula Theory
and the Sun
Don’t forget your sunblock!
The Sun
• Most important celestial object for life
on Earth
– Contributes heat  moderate temperatures
– Contributes light  visibility
– Photosynthesis  provides autotrophs with
energy to make food,  provides consumers
with food
Where Did it Come From?
• Current theory: Solar Nebula Theory
– Stars and planets formed together
• Star: Celestial body of hot gasses (H and He)
• Star formation
– A hot core surrounded by gas and dust
• Gas and dust = nebula
– Sometimes, this leftover material drifts into
space
– Sometimes, it remains in the nebula, bound by
gravity
How the Solar System Formed
How the Solar System Formed
• Gravity sets gas and
dust particles into
motion
– No resistance in
space!
– The closer the
particles get to each
other, the stronger the
force of gravity
• Particles aren’t
perfectly aligned so
they end up spinning
around in a nebula
How the Solar System Formed
• Spinning nebula
contracts and
flattens into a disc
– Accretion disc
• Particles begin to
gather in the centre
of the nebula
– Forming a protostar
(hot, condensed
object)
How the Solar System Formed
• Tiny grains or small lumps collect in
nebula
– Attract others and build up to bigger,
rocky lumps called planetismals
• If planetismals survive collisions, they
may build up to full planets like those
in our solar system
• If their mass is >10x that of Jupiter,
fusion begins and a star is formed
How the Solar System Formed
How the Solar System Formed
How the Solar System Formed
Extrasolar planets
• Many planets have
been discovered in
orbit about stars
other than the Sun
– “extrasolar planets”
• They can be detected
by
– A) the dimming of
their star’s light as
they pass in front of it
– B) direct photos
How the Sun Formed
• Nebula collapses, contracts, and gas
compresses
– Friction of all that material in nebula causes
a temperature increase
• At 10 000 000°C, nuclear fusion begins
– The combining of 2 atomic nuclei to form 1
large nucleus
– H + H  He + energy
Sun’s Nuclear Fusion
H
Small atoms
He
+ Energy!
H
Large atom
• 1 g of Hydrogen provides enough energy for a home in
Canada for about 40 years
Sun’s Nuclear Fusion
• H nuclei combine to form Helium
– Requires massive pressure and temp
– Now called “protostar”
• He is more dense that H
– :. He settles in Sun’s core
• Pressure in the core is very high. When
it balances with force of gravity pulling
in matter toward core = stable star
Sun’s Nuclear Fusion
Sun’s Nuclear Fusion
• When the sun converts ~ 10% of H to
He, He core accumulates and
undergoes fusion itself
– Sun changes physically
•
•
•
•
He core grows
H fusion (ring around core) also grows
:. The sun is growing… yowsa!
~ 30% larger than its protostar phase
Sun’s Nuclear Fusion
Structure of the Sun
• He core (where solar energy is produced)
• Radiative zone: 86% of sun’s energy radiates outward
from core
• Convective zone: outer layer transfers energy in
convection currents back in towards sun
• Photosphere: “surface” layer of sun
2 Important processes: Convection and Radiation
Features of the Sun
Sunspots
• Def: An area of strong
magnetic force on the
photosphere
• Sunspots are not dark,
they are bright
– Appear dark due to contrasting
temperature to photosphere
• Photosphere: 6000˚C
• Sunspot: 4500˚C
Sunspots
• By observing sunspots, astronomers
learned the sun rotates in 27-35 days
• Gradually grow, may fade and
disappear altogether
• Occur in 22-year cycles
Solar Flare
Solar flare: Magnetic fields
explosively eject intense
streams (solar wind) of charged
particles into space
Solar Flare
• If one of the streams hits Earth, it can:
– Disrupt telecommunication and electrical
equipment
– Usually beautiful auroras
• Shimmery curtains of high energy, charged
particles
• Electric currents charging gasses in Earth’s
atmosphere