Slide 1

Facts about the Sun
is 93 million miles from Earth
is made of 92% Hydrogen, 7% Helium, and 1% other gases
is 5 billion years old, another 5 billion to go
is a medium-size star, one of about 2 billion in our galaxy
has an 11-year cycle of solar activity

The Sun is our star

Solar Observing in the Space Age
Certain spacecraft orbits have unique advantages for solar observing.
The orbit of the ESA/NASA SoHO spacecraft, shown here, allows solar scientists to observe the Sun continuously, without interuption by periods of night, when the spacecraft is in the shadow of Earth.

Names of things on the Sun

We probe the Sun’s interior using helioseismology
Turbulence near the surface of the Sun generates sound.
Sound waves of certain frequencies are trapped inside the Sun.  These waves are refracted and reflected.  Certain wave lengths resonate,  like tones and overtones inside a musical instrument.

The patterns of resonating waves reveal the Sun’s interior structure and motions
The motions on the surface of the Sun are organized into patterns in both space and time, which reflect those waves which resonate inside the Sun.  Analysis of these patterns (blue means upward, red downward) allows us to infer the structure and motions hidden from direct view.
The pattern shown – like a certain musical note --corresponds to a certain integral number of wavelengths in latitude, longitude and radial depth.

The Doppler effect reveals ripples on the surface
Spectroscopic observations show up and down motions on the surface with no obvious pattern.   However, careful harmonic analysis shows that these motions are organized in millions of individual “notes”, or modes.
Four of these modes are shown here.

The Sun rotates faster at its Equator than its Poles
In the early 17th century, Galileo used sunspots to determine that the Sun rotates in about 27 days.  We now know that the  Sun is not a solid body.  Its equatorial rotation period rate is about 25 days, while the polar period is about 35 days.
Color code: Red is faster, blue is slower.
Helioseismology tell us that
this “differential rotation” extends far below the surface.

Earlier helioseismology results: plasma rivers
Rivers of gas flow under the surface.  Their motions are systematically faster and slower than average.  However, early observations did not span enough time to be able to see variations on the scale of the 11-year solar cycle.

Recent results: rotation is variable at all depths
Rotation rate variations are seen at depths from the surface to below the bottom of the convection zone, with 1.6 year period fluctuations seen over a five-year period.

Implications for magnetic fields: a dynamo
A dynamo is a mechanism for amplifying magnetic fields. In this model of the dynamo, differential rotation inside the Sun amplifies the primordial dipolar solar magnetic field by wrapping it up. When the field reaches a strength about 100,000 times greater than the Earth’s magnetic field, it buoys up to form active regions in the photosphere and corona.

The deep origins of the Sun Earth connection
Motions in the Sun’s interior are ultimately responsible for the dynamic eruptions of magnetic fields that are so important to the the Sun Earth connection.

Magnetic fields observed on the solar surface
This movie shows just over one solar rotation period.  In the black and white areas magnetic fields respectively emerge from, and descend back into, the solar interior.
Watch for:
New active regions emerging
Hemispheric differences
Faster rotation at the equator

Magnetic fields control the Sun’s atmosphere
The Sun’s atmosphere is strongly controlled by magnetic forces.  Where strong magnetic fields erupt from below (orange), they hold the gas down and the corona is bright.  In the polar regions, where no significant amounts of magnetic field emerge, the corona is dark because it can expand freely (red arrows) to form the solar wind.

We see different parts of the Sun’s atmosphere by looking in different colors
Different colors of light come from gases at different temperatures.  The white light you see with your eye comes from the cool photosphere and sunspots; X-rays come from the hot corona.

The Sun’s corona is filled with magnetic loops
This dramatic Yohkoh X-ray image shows many magnetic field lines arching into the Sun’s corona from below, forming active regions.  Readers of Sky and Telescope magazine (January 2000) chose it to be one of the 10 most inspiring astronomical images of the century!

Sunspot activity follows an 11-year cycle
Traditionally the number of sunspots defines the rise and fall of solar activity. This chart shows that the Sun may approach its peak level or “solar maximum” around mid-2000.

Comparing the Sun: 1996 to 1999
By comparing images of the Sun over two years apart, you can see a dramatic difference in its activity levels. This increase is caused by the emergence of more and stronger magnetic fields. (Sun observed in extreme ultraviolet light.)

A Coronal Mass Ejection (CME)
A CME is a cloud of hot magnetized  gas, weighing billions of tons, which is launched from the Sun at a speed up to millions of miles per hour. The CME shown in the sequence at the right was launched over an 8-hour period in 1996.
CMEs are caused by the breaking apart of magnetic forces. These occur almost every day, but most go off in other directions, not toward Earth.

CMEs busting out all over
This 16-day sequence during a very active period shows that CMEs occur often and in many directions..

How to recognize an Earth-bound CME

Sigmoids in the X-ray corona
CME’s tend to be launched from regions shaped like an S or reverse-S, called “Sigmoids”.  The sigmoid shown here erupted several times during the two days of the movie clip.

S marks the spot animation
The twisted magnetic fields of sigmoids store energy.

Space weather: a CME approaching Earth
It takes 2 to 4 days  for a CME blast to reach Earth, as  it expands up to 30 million miles wide. The white lines show the space filled by Earth’s magnetic field – the magnetosphere.

Earth’s Magnetosphere and a CME
Normal shape

Earth’s magnetosphere reacting to a CME
This supercomputer model was created by taking data from a number of instruments and developing a visualization of how the magnetosphere responded to a CME on Jan. 10, 1997. The clip shows a four hour period.

Auroras often occur when a CME hits Earth
    Often called the northern or southern lights, these often colorful and flashing light displays in the night sky are mostly seen at high latitudes near the poles.  They are caused by the impact of fast moving electrons from outer space (our magnetosphere) on the Earth's upper atmosphere.

The auroral oval
Most locations can only see aurora when the solar wind is active due to solar storms. Then the Earth’s magnetic field directs energized particles into oval rings (see dotted line) near the poles that thicken and spread towards the equator.

CME impact on Earth’s magnetosphere
Seen on Earth as aurora, the impact of a CME on Earth’s magnetic field is captured in an ultraviolet video from the perspective of a spacecraft.  The red areas indicate the most intense magnetic activity.

Aurora as seen from space

Powerful magnetic storm: 1989
In 1989, near the last solar maximum, a very strong solar storm impacted the Earth’s magnetosphere.  Quebec, Canada lost power  for 9 hours and power, navigational and communications systems around the world were upset.  This computer model shows how the storm moved in just a few minutes. (Red means highest level).

When CMEs impact our magnetosphere
.

How can we prepare for CMEs?
improve space weather monitoring & predictions
conduct research on the Sun-Earth connection
build stronger satellites and more protected systems
take operational precautions in response to warnings

Many related Web sites can be explored
Windows to the Universe
http://www.windows.umich.edu/
• engaging Web site that spans the Earth and Space sciences. Offers
classroom activities and resources.
NASA’s Education Program
http://www.hq.nasa.gov/education/
• introduces educators to NASA’s extensive available resources
NASA’s Space Image Libraries
http://www.okstate.edu/aesp/image.html
• a variety of sources for NASA’s space-related images
Views of the Solar System
http://www.hawastsoc.org/solar/homepage.htm
• an educational tour of the solar system, with images and information
 about the Sun, planets, moons, asteroids, comets and meteoroids

Web sites about the Sun Earth Connection
Sunspots and the Solar Cycle
http://www.sunspotcycle.com
• about sunspots, solar flares, and the status of the solar cycle.
Solar Storms and Their Human Impacts
http://image.gsfc.nasa.gov/poetry/storms/storms.html
• about effects of solar storms on satellites and power systems
Helioseismology and Much Much More
http://solar-center.stanford.edu
• an award-winning solar site for kids from 6 to 60

Acknowledgements
Thanks to all who contributed images and movies to this presentation:
National Space and Aeronautics Administration
European Space Agency
Institute for Space and Astronautical Science, Japan
The SoHO team: esp. Steele Hill & Bernhard Fleck
The Goddard Public Affairs Office
National Science Foundation
National Solar Observatory