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The Sun
Did You Say the Sun Has Spots?

Yes! The spots are storms on the superhot Sun and they are keeping Earth aglow, according to the U.S. space agency.

Noting that the Sun is especially hot right now, NASA says our star is spewing out electromagnetic radiation in the midst of an interesting storm season. A lot of that energy arrives at Earth.

However, even as plasma and high-energy particles from the Sun light up Earth's ionosphere, orbiting detectors and other scientific equipment compose an early-warning system help us keep satellites in space and power grids on the surface of the planet safe.

Solar Cycles. Sunspots can be seen to vary on the face of the Sun in eleven-year actvity cycles. They have been watched for centuries, but only recently have scientists understood that they eject hot electromagnetic plasma.

NOTE: you never should look directly at the Sun for any reason. Doing so can damage your eyesight. At any rate, sunspots are invisible to the naked eye. Of course, their effect can be seen as they light up Earth's northern skies with Aurora Borealis.
Satellite views »

Cycle Numbers. Scientists have been numbering the solar cycles since 1755. The current sunspot cycle is number 23. It is expected to end early in 2007. Here are the dates for the cycles:
1March 1755June 1766
2June 1766June 1775
3June 1775September 1784
4September 1784May 1798
5May 1798December 1810
6December 1810May 1823
7May 1823November 1833
8November 1833July 1843
9July 1843December 1855
10December 1855March 1867
11March 1867December 1878
12December 1878March 1890
13March 1890February 1902
14February 1902August 1913
15August 1913August 1923
16August 1923September 1933
17September 1933February 1944
18February 1944April 1954
19April 1954October 1964
20October 1964June 1976
21June 1976September 1986
22September 1986May 1996
23May 1996circa2007

The Latest Solar Maximum. Solar scientists calculated that the Sun reached the peak of its most-recent eleven-year sunspot activity cycle in April 2000. The so-called "solar maximum" is the two-to-three year period around the peak of activity when the Sun appears most tempestuous and Earth is buffeted with powerful solar gusts.

The Solar Cycle 23 peak seems to have been the month of April 2000 when the smoothed sunspot number (SSN) was 120.8.
Chart depicting the progression of the solar cycle »

What are smoothed sunspot numbers? When the daily sunspot count is plotted over a month's time, the graph is very spiky. Averaging daily sunspot numbers over a month results in the monthly average sunspot number, however it also results in a spiky plot. A smoother plot is desired by researchers. To get that, they choose a more averaged, or smoothed, measurement to measure solar cycles. This is the so-called smoothed sunspot number (SSN) calculated across five and a half months of data before and after a desired month, plus the data for the desired month. The amount of smoothing leaves the official SSN a half year behind the current month.
Frequently asked questions about solar indices »

Cycle 23 like Cycle 20. Solar scienists suggest that Cycle 23 is much like Cycle 20 was in the way it rose and fell. Cycle 20 took about four years to reach peak and about seven uears to descend to minimum. If the two are alike, that could mean that Cycle 23 will reach bottom in 2007. The peak of Cycle 24 then could come in 2011.
Charts for solar cycles 1 - 20 »


Space is not a vacuum. In our Solar System, it's filled with plasma – a low-density gas of charged atoms.

The Sun's temperature is so high that our star's powerful gravity can't hold onto its gas. On a typical day, plasma streams out from the Sun in all directions at about a million miles per hour – the solar wind.

Solar astronomers think of those typical days as quiet. Occasionally, there are non-typical days when humongous explosions on the surface of the Sun – coronal mass ejections – fire material outward at up to ten times the speed of quiet days.

As the CME matter spreads out rapidly from the Sun, it drives a shock-wave that excites the quiet particles it hits to high energy levels.

When a shock-wave passes Earth, our planet's magnetosphere is disturbed causing a geomagnetic storm.
Magnetic flip. An additional indication that Cycle 23 peaked in the year 2000 came in a NASA report in February 2001 that the Sun's magnetic field had flipped. That means that Sun's north pole, which had been in the northern hemisphere of the Sun before the flip, now is in the southern hemisphere.The flip really wasn't a surprise since it seems to happen at the peak of each solar cycle.

Negative Effects. Sunspots throw masses of coronal material out from the Sun. The particles take three days to reach Earth where the mass of plasma can send satellites tumbling and stress power systems. In the 20th century the solar maximum was known to have changed the computer programming inside orbiting satellites and shut down power grids on the surface of our planet.
  • The Challenger disaster of 1986 had set shuttle flights back three years. NASA had to loft the Hubble Space Telescope in a shuttle, but had trouble scheduling a launch. There was a shortage of fuel and competing demands for rides pushed the flight to a time when the Sun was blossoming with sunspots. An eleven-year peak in the sunspot cycle was approaching. Those exploding gases on our star heated Earth's upper atmosphere, expanded it deeper into space and caused extra drag on satellites. That threatened to pull the 12-ton, 43-ft. Hubble down to a lower orbit from which it might fall to Earth like a meteor. The sunspots gave NASA an exasperating choice -- launch Hubble so high a shuttle might not be able to reach it for repair, or launch it so low shuttles would have to fly every six months to boost it higher. The agency decided to delay launch to prevent frequent service flights. At last, Hubble was loaded aboard Discovery and on April 24, 1990, ferried to an orbit.

  • Solar storms during the period of peak sunspots in 1989-91 caused power failures in Canada and Sweden, made some computers crash in the United States, and destroyed or damaged several satellites.

  • During the sunspot peak in 1989, a blast of solar energy arriving at Earth shut down the electrical power grid in the Canadian province of Quebec, leaving six million customers in the dark for a day.

  • Global Positioning System (GPS) satellites tell users where they are within a few feet. If, for instance, solar energy caused them to provide less accurate data for a few hours, that could cause problems for airplanes landing.
After the 1989-91 problems, NASA, NOAA and other government agencies rushed to set up an early-warning system. Predictions are better today, but not yet perfect.
  • Power operators along the East Coast of North America were alerted to respond promptly to a solar burp in July 2000. They cut the output from their generators to avoid overloads. Even so, their transformers overheated and circuit breakers tripped.
Satellites Report Outbursts. As the Sun's most recent stormy season peaked in the year 2000, solar scientists used their coordinated fleet of satellites and ground observatories to watch out for angry outbursts of solar radiation and predict the impact of turbulent space weather.

By combining imporved new instruments with time-tested older equipment, researchers are able to make timely predictions of space weather events more accurately. Data from space feed directly into NOAA computer programs for forecasting space weather and its effects on Earth systems.
  • The Solar and Heliospheric Observatory (SOHO), a project of the European Space Agency and NASA, and NOAA's Geostationary Operational Environmental Satellites (GOES), in July 2000 tracked and predicted an intense solar storm nicknamed the "Bastille Day event."

    Bastille Day, on July 14, is the French symbol of the end of its monarchy and the beginning of the First Republic.

    Adding data from observatories on the ground, scientists predicted a bright solar flare and its energetic proton shower July 13. The flare coincided with a coronal mass ejection, which sent billions of tons of plasma into space traveling at four million miles per hour, two times faster than normal.
    Satellite views »

  • The Advanced Composition Explorer (ACE) satellite, orbiting above Earth, detects the shock waves of particles arriving at the outer edge of our planet's atmosphere. A shock wave is the leading edge of an ejection that is something like a wave you might see pushing in front of a boat in water. NOAA space weather forecasters, using ACE data, can provide a one hour notice before the start of a geomagnetic storm. That is, about one hour's notice before the shock waves pound into Earth's magnetosphere -- the magnetic barrier that surrounds our planet. The shock waves cause an effect like the striking of a bell. Vibrations move up and down the entire magnetosphere.

    Unfortunately, the "Bastille Day" solar shower blinded some of the key detectors inside ACE itself. Without reliable data, NOAA space weather forecasters had to wait until Earth's magnetic field became distorted before they knew that the disturbance had arrived.

    That "G5" geomagnetic storm -- the most intense classification -- raged for nearly nine hours after the solar shower impact. Its effects were widespread. Cameras and star-tracking navigation devices on several satellites were flooded with solar particles. Measurements from particle detectors and other instruments on several NOAA and NASA satellites were either degraded or shut down temporarily. The Japanese Advanced Satellite for Cosmology and Astrophysics (ASCA) was sent tumbling in orbit.

    On the ground, aurora light shows could be seen as far south as El Paso, Texas. Power companies' delivery systems suffered overloads of geomagnetically induced currents that tripped capacitors and damaged at least one transformer. GPS satellite accuracy was degraded for several hours. The July 2000 "Bastille Day event" had surprised users who hadn't seen such solar activity for a decade.
    Satellite views »

  • The Imager for Magnetosphere to Aurora Global Exploration (IMAGE) satellite photographed the effect of the shock wave on Earth's aurora, which lit up in a very spectacular way.

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