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

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 17^th 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


	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


	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.


	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 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.


	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.


	In the early 17^th 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.


	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.


	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.


	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.


	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.


	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


	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.


	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.


	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!


	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.


	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 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.


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


	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.


	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.


	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.


	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.


	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.


	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.


	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).


	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


	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


	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


	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