Notes

Outline

Slide 1

Facts about the Sun is 93 million miles from Earth sends its light to Earth in about 8 minutes 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

Other stuff about the Sun

The Sun is big! The Sun is almost a million miles across.

Names of things on the Sun

The Sun is the source of all our energy Every second, millions of protons in the Sun's core collide with other protons due to powerful pressures to produce helium nuclei in a fusion reaction that releases energy.

The Sun’s energy comes from its core The powerful fusion process that provides the Sun’s energy takes place in its core.  Once generated, this energy passes out through the stable radiative zone (bright yellow) to the turbulent convection zone (gold).

You can see different parts of the Sun 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 rotation The Sun rotates about every 27 days.  Over a 10 day period, while Sun rotates, it reveals several regions of magnetic activity.  Many changes take place – the Sun is far from constant. The green color used here is false – it is simply added so scientists can easily know which wavelength was used.

Sunspots Darker and cooler areas on the Sun are caused by strong magnetic fields.  They last from several hours to several months. The number of spots you can see goes up and down with the rise and fall of the solar cycle (11 years).

Sunspots underlie coronal active regions As we look at the Sun in various colors, we can see the relationship between features of the million-degree corona and those of the 6000-degree photosphere, such as sunspots, that underlie them.

The Sun’s magnetic field The Sun is strongly affected by magnetic forces. The red arrows show the polar field lines of the Sun’s global magnetic field. The orange field lines show the magnetic field lines of the active regions.  Each active region has its own pair of North and South polarities.  The field lines joining them form the graceful arching loops seen in Yohkoh X-ray images.

Coronal Active Regions This dramatic Yohkoh X-ray image of the Sun’s corona was taken in 1991, a few years after the last solar maximum.  It was chosen by a poll of readers of Sky and Telescope magazine (January 2000) as one of the 10 most inspiring astronomical images of the century.

The Solar Cycle The Sun follows an 11-year activity cycle. One indicator of solar activity is the number of sunspots. This chart shows that the Sun should 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.

Strong CME and proton blast Near the end of this two-day movie, a solar flare occurs. The flare propels high-energy protons from the Sun to the spacecraft (92 million miles away) within just one hour.  When the protons hit the spacecraft’s sensors, they cause a pattern of white specks, or “snow”

Solar flares from an active region This movie captures the dynamics of a solar storm building up then blasting big solar flares twice over a 4-day period. Flares are intense and impulsive explosions on the Sun that propel high-energy protons into space.

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.

Spectacular aurora

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 resources available 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 Solar Max Sunspots and the Solar Cycle http://www.sunspotcycle.com • about sunspots, solar flares, and the latest news about the solar cycle. NOAA’s Space Weather page http://www.hq.nasa.gov/education/ • about current weather conditions in space near earth, including forecasts; a good site for learning about whether there might be an aurora tonight. 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 Max Millennium page at MSU http://solar.physics.montana.edu/max_millennium/press • a page of links to these and many other sites