The Sun – Our Favorite (and
Ordinary) Star
Features of the Sun
Layers of the Sun
 The
sun’s interior layers
 Core – where hydrogen fusion
happens.
 Radiative zone – energy carried
toward surface by radiation (as
light).
 Convective zone – energy carried
toward surface by convection (as
heat).
Layers of the Sun
 Sun’s
atmosphere (Outer Layers)
 Photosphere: lowest layer, emits
visible light, granulation – what we
see.
 Chromosphere: middle layer,
transparent, has spicules.
 Corona: upper layer, transparent,
source of solar wind.
ATMOSPHERE of the Sun – 3 layers
The Photosphere
• The bright visible surface of the Sun is
called the photosphere.
The Photosphere
Granulation:
 the marbled pattern seen on the sun’s surface
 caused by the convection of gases just beneath
the photosphere.
The Chromosphere
 Above the photosphere
 Sometimes visible during an eclipse
 emits only certain wavelengths of light, resulting
in a reddish appearance.
 Spicules rise up from here
Spicules are jets of gas that extend upward
from the chromosphere.
THE CORONA
• Source of solar wind, a stream of radiation
released far into space
• Earth’s magnetic field (magnetosphere) protects
us from solar wind.
Differential Rotation of the Sun
Because the sun is made up of freely moving gases, it
has a slower period of rotation at the poles than at the
equator. This is called differential rotation.
The rotation period of the Sun’s gases varies from 25
days in the equatorial region to 35 days near the poles.
Differential Rotation – cont.
 Causes the sun’s magnetic field.
 Magnetic field lines of the Sun become bent, creating regions
of intense magnetic fields.
 Magnetic fields produce sunspots and other spectacular
features.
Features Caused by the Sun’s
Magnetic Field
Sunspots – areas of concentrated
magnetic field lines. They occur in pairs
 Prominences – magnetic loops above
sunspots, can carry plasma (hot ionized
gas).
 Flares – twisted magnetic field lines relax
and release huge amounts of X-rays.
 Coronal Mass Ejections (CMEs) – twisted
magnetic field lines relax and release huge
amounts of plasma.

Sunspots
•
•
•
•
•
Dark spots on the sun’s surface
Occur in pairs
Act like 2 poles on a magnet
Regions of intense magnetic fields
Can be used to determine the sun’s rate of
rotation
• The amount of sunspot activity has an 11 year
cycle
The number of sunspots on the photosphere varies
over an eleven-year cycle.
Sunspot Maximum
Sunspot Minimum
Sunspots can be used
to determine the rate
of the sun’s rotation.
Prominences
• Ionized gases trapped by magnetic fields form
prominences that arc far above the solar surface.
• Sometimes these gases are ejected into space.
Solar Flares
 Violent eruption of all forms of
electromagnetic radiation (no
matter)
 Travels at the speed of light
 Form when the arcs of more
than one prominence touch
and short circuit.
 Caused by a build up of
magnetic energy in the solar
atmosphere.
 Associated with sunspots
 Often associated with coronal
mass ejections.
Coronal Mass Ejections
 Powerful plasma (matter)
and radiation eruptions that
originate near the sun’s
surface
 Billions of tons of matter are
released into space
 Matter from a CME can
reach Earth in 1-4 days
 Driven by kinks in the sun’s
magnetic fields
What is the Difference?
http://www.universetoday.com/114729/nasa-explainsthe-difference-between-cmes-and-solar-flares/
An artist’s depiction of a
coronal mass ejection of
radiation and matter
Matter is fortunately deflected
away from Earth by our
magnetic field.
By following the trails of gases released during a
coronal mass ejection, we can map the Sun’s
magnetic field.
What Powers the Sun?
• Nuclear fusion, which converts hydrogen into helium.
• Matter gets turned into energy
E = mc2
Fusion of Hydrogen into Helium
E = mc2
Hydrostatic Equilibrium
 The Sun’s interior is held stable by a balance between
radiation pressure forces and gravity
GRAVITY – pulls in
RADIATION PRESSURE FROM
HYDROGEN FUSION – pushes out
THE SOLAR
INTERIOR
Review

How does the mass of the Sun compare
with that of the rest of the Solar System?


Are there stars nearer the Earth than the
Sun is?


The Sun contains almost all (99.85%) of the
Solar System’s mass.
No, the Sun is our closest star.
Does the Sun have a solid and liquid
interior like the Earth?

No, the Sun is composed of hot gases.
Review

What is the surface of the Sun like?


Does the Sun rotate?


The Sun has no solid surface, and no solid or
liquids anywhere. The surface we see is
composed of hot, churning gases.
The Sun’s surface rotates differentially; once
every 35 days near its poles, and once every
25 days near its equator.
What makes the Sun shine?

Thermonuclear fusion in the Sun’s core.