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Largest Solar Flare Recorded by SOHO Spacecraft

© Pattie Stechschulte

Just as the biggest sunspot (AR9393) was moving through the sun's regular 27-day rotation in early April, it unleashed the largest solar flare in recorded history.

The flare occurred in the northwest corner of the Sun's surface, but it was not directed at Earth. It did disrupt radio communication to satellites on the sunlit side of the Earth because X-ray and ultraviolet light from the flare affected the ionosphere. The flare was recorded by the Solar and Heliospheric Observatory (SOHO) spacecraft, which is a joint mission between the European Space Agency (ESA), the National Aeronautics and Space Administration (NASA) and other international groups.

Spacecraft and Instruments

A NASA rocket launched the European-built SOHO spacecraft in late 1995, and then it reached a location called Lagrange Point No. 1 about 1 million miles from Earth. The SOHO project has been international projects with 15 countries contributing to the construction and scientists from 62 institutes operate the continuing functions on spacecraft.

From that site, SOHO has recorded a variety of activities occurring on the Sun's surface, including over 3,600 coronal mass ejections and 30 eruptions. SOHO has also made history by identifying approximately 300 new comets, the most by any one mission in astronomy history. Onboard the spacecraft are two important instruments - the Solar Wind Anisotropies (SWAN) and the Michelson Doppler Imager (MDI).

The SWAN telescope can map the whole sky in ultraviolet light, which can see UV "hot spots" caused by active regions on the far side of the Sun. While the MDI instrument peers right through the Sun to locate hidden sunspots and their active regions. Basically, the MDI pinpoints hidden sunspots while SWAN's data reveal how active they are.

"When we started work with SOHO five years ago, most experts thought it would be impossible to see right through the Sun," comments Philip Scherrer of Stanford University, principal investigator for the MDI instrument. "Now we do it regularly in real time. For practical purposes we've made the Sun transparent."

What SOHO Has Uncovered

During the past five years, SOHO has recorded some fascinating discoveries about our Sun, including:

- A pulse-rate of gas currents that occur in a 16-month cycle from the Sun's core to the surface.

- High-energy ultraviolet rays have become stronger; 3 percent in the last 300 years scientists estimate.

- Predicts outbursts of gas from coronal mass ejections effecting Earth.

- Discovered solar tornadoes on the Sun's surface the size of Africa that spiral outward from the polar regions with wind speeds of 31,068 miles per hour.

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