The third most powerful solar flare ever recorded erupted from the Sun earlier today, and scientists say Earth could feel the effects with communications disruptions and loss of power.

Image from SOHO today showing the eruption. Credit: NASA/ESA/SOHO

At about 6 a.m. EST (1100 GMT), satellites watched as the event occurred. The flare was significantly larger than several unleashed since last week.

"This is the real thing," says John Kohl, a solar astrophysicist at the Harvard-Smithsonian Center for Astrophysics (CfA) and principal investigator for the Ultraviolet Coronagraph Spectrometer on board NASA's Solar and Heliospheric Observatory (SOHO) spacecraft.

"The eruption was positioned perfectly. It's headed straight for us like a freight train, so a major geomagnetic storm is bound to happen when it reaches us on October 29th or 30th."

"It was slightly more powerful that the famous March 6, 1989 flare which was related to the disruption of the power grids in Canada," Dr. Paal Brekke, the European Space Agency SOHO deputy project scientist reported.

Image from SOHO today showing the eruption. Credit: NASA/ESA/SOHO

Today's solar flare was classified as an X18-category explosion, meaning that it can trigger planet-wide radio blackouts and long-lasting radiation storms.

"Last week's (coronal mass ejection) hit the Earth with only a glancing blow," says Kohl, although it was sufficient to disrupt airline communications. "Today's eruption was pointed directly at us, and is expected to have major effects."

"We are waiting for the prediction of the geomagnetic storm level from NOAA (the National Oceanic and Atmospheric Administration)," says Kohl. "What we know at this point is that the flare was nearly perfectly positioned near the center of the Sun, and that a halo coronal mass ejection has left the Sun and is heading toward the Earth. The geomagnetic storm is likely to be a strong one, and will last about 24 hours."

"We may be in for some great aurora," Brekke said.

Such solar storms have the potential for knocking out communications and power grids on Earth, and can be harmful to orbiting satellites and astronauts.

The International Space Station's current resident crew -- commander Michael Foale and flight engineer Alexander Kaleri -- will protect themselves by moving to a portion of the outpost that provides the most shielding from radiation.

Image from SOHO today showing the eruption. Credit: NASA/ESA/SOHO

NOAA classifies geomagnetic storms on a scale from 1 to 5. Initial indications show that this has the potential to be a G5 storm - the top of the scale. The most benign effect of such a storm would be bright auroras visible from more southern latitudes than usual. However, the geomagnetic storm triggered by the CME also could interfere with satellite communications; disrupt power grids (as occurred in the 1989 Quebec blackout); even short out orbiting satellites, rendering them permanently inoperable.

"We've already had to shut down our SOHO instrument for safety reasons. It's getting blasted by high-energy particles from this solar flare," says Kohl. "Of more concern, geosynchronous communications satellites are likely to be affected." In California, where raging wildfires have damaged many microwave communication antennas on the ground, satellite communications have been crucial to emergency efforts. Emergency personnel should be prepared for potential disruptions and communication interference.

"There's no direct danger to people on the ground," Kohl adds, "and I'm sure that NASA is monitoring the situation for any potential effects on the space station crew, and that they are taking appropriate precautions."

According to NOAA, a G5-class geomagnetic storm can have the following effects:

Power systems: Widespread voltage control problems and protective system problems can occur, some grid systems may experience complete collapse or blackouts. Transformers may experience damage.

Spacecraft operations: May experience extensive surface charging, problems with orientation, uplink/downlink and tracking satellites.

Other systems: Pipeline currents can reach hundreds of amps, HF (high frequency) radio propagation may be impossible in many areas for one to two days, satellite navigation may be degraded for days, low-frequency radio navigation can be out for hours, and aurora has been seen as low as Florida and southern Texas (typically 40 degrees geomagnetic lat.).