The Sun to the Earth - Stanford Solar Center
The Sun to the Earth - Stanford Solar Center
The American Geophysical Union
Space Physics and Aeronomy Section
The American Geophysical Union (AGU)
Space Physics and Aeronomy (SPA) Section
Solar and heliospheric physics - the study of the Sun
and solar variability together with the composition,
structure, and dynamics of the interplanetary medium
and its interaction with the local interstellar medium
Magnetospheric physics - the study of the
plasmas, magnetic and electric fields, and current
systems in the magnetospheres of the Earth and
Aeronomy - the study of the ionized and neutral
upper atmospheres of the Earth and planets and
of their interactions with their respective space
Our Sun is a turbulent, active star
that can have
effects on the
The Sun’s place in the Galaxy
The Sun is one of about 200 billion stars in a galaxy we call Milky Way.
It resides on the outskirts, about 28,000 light years from the center.
Why Study the Sun?
• Understand how the Sun affects the Earth and the solar system
• Understand how stars work
• Understand more about the laws of nature
The Sun is the only star known to grow vegetables.
(Dr.Philip Scherrer, Stanford University)
(just the facts)
• 150 million km from Earth
• 1.4 million km across = 109 Earths
• 4.5 billion years old
• 2x1030 kg mass. (333,000 times
the mass of the Earth)
• 75% hydrogen, 24% helium, 1%
• Makes up 99.98% of the mass of
the solar system
Surface: 5800 degrees K. (10,000 degrees F.)
Core: 15.6 million K. (280,000 F.)
What color is the Sun?
The Sun appears white
radiates in all
The electromagnetic spectrum
The Sun from the Inside Out
Knowledge we gain about the Sun can be applied to other stars.
What makes the Sun hot?
Fusion in the Sun’s core produces heat/energy
The Sun’s Roiling Surface
Size of Earth, for
Like fudge or oatmeal cooking, the
Sun’s surface boils up with heat,
then crashes down
As the Sun turns
Like the Earth, the Sun rotates. However, unlike the Earth,
the Sun has a complex rotation mechanism.
The Sun’s Variable Rotation
Solar Rotation Rates:
1) Polar regions = 36 days
2) 60 Degrees = 31 days
3) Equatorial Regions = 26 days
The Sun is a ball of gas. Different regions rotate at different speeds,
both in the interior and on the surface, resulting in differential rotation.
The Earth is solid and rotates at one speed (~24 hrs/day).
How do we know about the
interior of the Sun?
Helioseismology is the technique of studying low frequency,
primarily sound, waves to probe the inside of the Sun,
Acoustic waves “bouncing
around” in the solar interior.
regions of strong
magnetic fields. They
appear dark because
they are relatively cooler
than the surface.
Sunspots and Magnetic Fields
Sunspots appear around regions of strong magnetic fields
How do magnetic fields
cause solar activity?
Most sunspots and
events on the Sun
are caused by
eruptions and tangles
of complex magnetic
Seeing Magnetic Field
traces out magnetic
fields in the solar
What happens below a sunspot?
New techniques allow us to study gas flow
beneath a sunspot.
The 11 year
The amount of
on the Sun varies
in an 11 year cycle.
A regular cycle of sunspot numbers
over the past 300 years.
Comparing the quiet and active Sun
Changes in solar activity after only 3 years
Dramatic changes occur
during the solar cycle
X-ray and magnetic activity
Sunspots appear at different latitudes
throughout the solar cycle
June 12, 2000
Jan 7, 2004
Common during the
Sun’s active periods
Huge flare of 28 October 2003
Solar prominence dwarfs Earth
Classifications of solar flare intensity
Categories A & B -- Small
Category C -- larger but few
noticeable consequences to Earth
Category M – Medium; cause radio
blackouts that affect Earth’s polar
Category X – major events that can
trigger planet-wide radio blackouts and
severe radiation storms
Chart (2 channel) from 2-5 November 2003
shows 4 X-class and many B, C, and M class flares
Category X28 flare, largest ever
recorded, erupts on November 4, 2003
Explosions on the Sun
(Coronal Mass Ejections)
A billion tons of hot gas
being launched from the
White circle in image indicates size and location of Sun,
which is blocked by a metal disk in the instrument.
Source of Flares and
Coronal Mass Ejections?
Magnetic field lines poke through the solar
surface, producing sunspots, flares, and coronal
Beyond the Sun
The Sun’s corona, or atmosphere, is visible during a solar eclipse.
Special telescopes can study the corona
by creating an artificial solar eclipse.
The white circle in the images indicates
the size and position of the Sun.
A solar “wind” streams into
the solar system and shapes
The Earth’s magnetosphere is buffeted during a
The Sun generates
Space Weather in our
Solar activity can have a dramatic impact on
communications, satellites, and astronauts.
Solar activity causes
Solar storm causes blackout in 1989
In 90 seconds, 6 million
people lost power for 9
An October 2003 solar
storm knocked out the
Mars Odyssey probe
affects the Moon
and other planets
we hope to explore.
Solar storms affect the Earth’s ionosphere
and interfere with communications.
Space Physics &