Our Star, the Sun
The Sun is the Largest Object in
the Solar System
• The Sun contains more than 99.85% of the
total mass of the solar system
• If you put all the planets in the solar system,
they would not fill up the volume of the Sun
• 110 Earths or 10 Jupiters fit across the
diameter of the Sun
How big is the Sun?
The Sun goes through periods of
relative activity and inactivity
The Sun’s interior
has three layers:
(1) core
(2) radiative zone
(3) convective
zone
Energy generated in the core of the Sun propagates outward
through these different layers, and finally, through the
atmosphere of the Sun. This process takes tens of thousands
of years or more.
The Sun’s atmosphere also has three
layers…
• Photosphere - the layer we see, 5800 K
• Chromosphere - the red layer observed
using a hydrogen filter, 10,000 K
• Corona - the incredibly thin outer
atmosphere, 1,000,000 K
Granulation caused by convection
The
photosphere is
the visible
layer of the
Sun
http://www.whfreeman.com/universe6e - Seething Granules around a Sun Spot
Sunspots are the most well known feature in the
photosphere. Monitoring sunspots reveals the
Sun’s rotation.
The
movement of
sunspots
reveals that
the Sun’s
rotation takes
about …
4 weeks
The annual change in numbers of sunspots reveals
that the Sun experiences an 11-year Sun Spot cycle
Maximum
number
Minimum
number
Magnetic field lines connect sunspots on the Sun’s photosphere
Above the photosphere, the chromosphere is
characterized by its red color –
from Ha emission.
Solar magnetic fields also create
other atmospheric phenomena
• prominences
Solar magnetic fields also create
other atmospheric phenomena
• prominences
• solar flares
The corona, the outermost part of the Sun’s
atmosphere, is characterized by its high
temperature and low density
The Sun also
ejects a stream
of charged
particles into
space known
as the solar
wind
Solar magnetic fields also create
other atmospheric phenomena
• prominences
• solar flares
• coronal mass
ejections
(CMEs)
The most powerful solar flare in 14 years, ..
erupted from sunspot 486 in late October of
2003. The explosion hurled a coronal mass
ejection almost directly toward Earth, which
triggered bright auroras when it arrived on
Earth.
The Earth’s magnetic field is caused by
movement of material in Earth’s interior
The Earth’s magnetic field produces a
magnetosphere that deflects and traps
particles from the solar wind protecting Earth
Relevance of Earth’s protective
magnetosphere
• Protects against Solar Flares - violent explosions
on the Sun releasing large burst of charged
particles into the solar system
• Protects against Solar Wind - dangerous stream
of charged particles constantly coming from the
Sun
• Northern Lights (Aurora Borealis)
Northern Lights (Aurora Borealis)
As the charged particles from the Sun interact
with the magnetic field around Earth, the
particles collide with the nitrogen and oxygen
atoms in the atmosphere and excite those
atoms to emit light
Aurora as seen from space