What is Solar Max?
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 What is Solar Max?
This image is comprised of 12 X-ray images of the sun's atmosphere taken between 1991 and 1995 in 120-day increments. This composite image clearly demonstrates how the sun changes during the solar cycle. The images were taken from the Yohkoh satellite, and can be found on the Yohkoh SXT site.

Scientists became aware that the sun went through cycles and changes by observing sunspots, the darker, relatively cooler areas of the sun. The number of sunspots can be an indication of the degree of solar activity. The average number of visible sunspots varies over time, increasing and decreasing on a regular cycle of between 9.5 to 11 years, on average about 10.8 years. An amateur astronomer, Heinrich Schwabe, was the first to note this cycle in 1843. The part of the cycle with low sunspot activity is referred to as "solar minimum," the portion with high activity is known as "solar maximum." The year 2000, it is believed, will be the solar maximum for the current solar cycle.

Solar Flares and CMEs
While sunspots have been used historically to indicate levels of solar activity, other solar features increase in number and intensity along with the fluctuations in the sun's magnetic field structure. Coronal mass ejections (CMEs) and emissions of high-energy solar flares become more common and more intense during the period of solar maximum. This increase in solar activity can affect us here on earth (and in earth's orbit) by what is known as space weather.

This NASA illustration shows the earth's magnetosphere and its interaction with the sun.
Effects on Earth
Ordinarily, the earth's own magnetic field protects it from most of the sun's emissions. But during periods of intense solar activity geomagnetic storms can produce heightened, spectacular displays of the Aurora Borealis and Aurora Australis, known as the Northern and Southern Lights. Geomagnetic storms can also disrupt radio transmissions and affect power grids. Energetic electromagnetic bombardments can interfere with the transmission of radio waves and the flow of electric current in wires. Radio operators are familiar with solar maximum and have to deal with an increase in static on the airwaves. Occasionally, radio signals can be completely drowned out. Power grids can be overloaded by these same bombardments. In 1989, during the last solar maximum, the power grid that supplies Canada's Quebec province was knocked out by a geomagnetic storm.

Satellite Disruption
Since satellites are outside the protection of the earth's atmosphere, they are particularly vulnerable to the severe geomagnetic storms that can result from solar activity. According to stellar physicist David Dearborn, "As the accelerated energetic gas particles from the sun interact with the earth's magnetic field...they slide around the earth and form current sheets that satellites have to deal with. Satellites move from a region of space that has one charge to an area that has another charge, and when they cross those boundaries, the surface of the satellite can suddenly change polarity (as it moves into a region where there is a different electric field). You get arcing and you get electric currents flowing inside the satellite in places where they're not supposed to flow, and that can be very bad for the satellites."

"Satellite drag" caused by the previous solar max, helped bring down Skylab early.
In addition to these polarity changes which can damage sensitive electronics in satellites, the increased solar emission also causes the earth's atmosphere to "puff out," creating increased drag on orbiting satellites. This increased drag can cause satellite orbits to decay more rapidly than predicted. The 100+ ton Skylab station is a good example. Launched in 1973, the station was supposed to remain in orbit until the 1980s. The purpose of Skylab was, among other things, to study the sun. Ironically, due to increased solar activity, Skylab re-entered earth's atmosphere in 1979--raining debris over the Indian Ocean and parts of Western Australia.

Solar Max 2000
It has yet to be seen whether the upcoming solar maximum will affect us here on earth (or in earth's orbit) in the way some of the past maximums have. Scientists still don't completely understand all of the aspects of the solar cycle and it's difficult to predict just how strong the solar maximum will be. Each of the 22 solar cycles studied since the one Heinrich Schwabe noted in 1843 has varied in intensity. One thing is certain, this current solar cycle, #23, will be the most closely observed ever. There will be nearly one dozen space-based observatories watching the sun during this solar maximum. We'll be watching, too, as we continually update Solar Max 2000 throughout the year.
 Glossary of Solar Terms
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 More on Solar Max

Solar Max in the News (Full Guide)
What is Solar Max? (RealVideo)
Should we be concerned about Solar Max? (RealVideo)
What can Solar Max teach us? (RealVideo)
Papers & Studies:
Space Studies Board - Upcoming Solar Maximum
Space Environment Center: Short Topic Solar Maximum (PDF format)

 Resources on Sunspots

 •  What are sunspots? (RealVideo)
 •  The Exploratorium's Guide to Sunspots
 •  MSFC Solar Physics: The Sunspot Cycle
 •  Sunspots and Solar Cycle: Science@NASA

  Solar Flares and CMEs

What are solar flares? (RealVideo)
What are coronal mass ejections (CMEs)? (RealVideo)
Solar Flares from the Marshall Space Flight Center Solar Physics site.
Coronal Mass Ejections from the Marshall Space Flight Center Solar Physics site.
What are CMEs? - Space physicist Nancy Crooker from Boston University describes CMEs (RealAudio). From the Exploratorium.

  Space Weather

What is space weather? (RealVideo)
Science@NASA/ SpaceWeather.com - Science news and information about the sun-earth environment.
NASA / NOAA: Daily Reports- From "Solar Max in the News" section.

 Auroras and the Earth's Magnetosphere

The Aurora: Information and Images from the University of Alaska Geophysical Institute.
Auroras: Paintings in the Sky - A self-guided introduction to the Northern Lights, from the Exploratorium.
The Exploration of the Earth's Magnetosphere - An overview of space research on the "Earth's environment in space."
Aurora & Geomagnetic Forecasts and News - From "Solar Max in the News" section.

 Solar Maximum Predictions

Sun Cycle Predictions from the Marshall Space Flight Center Solar Physics site.
Predicting Solar Maximum from the Planetary News.
Space Weather at the Next Solar Maximum from the Swedish Institute of Space Physics.
Solar Cycle 23 Project: Summary of Panel Findings from the NOAA Space Environment Center (SEC), with the support of the NASA Office of Space Science.

 Upcoming Sun-Earth Missions
HESSI spacecraft launches March 28, 2001.

 NASA Sun-Earth Missions

 •  The HESSI EPO Home Page
 •  The HESSI UCB Home Page
 •  SOHO: The Solar and Heliospheric Observatory
 •  Yohkoh Public Outreach Project


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