A Star With Two North Poles

Credit: Brian Grimm and LivingText An artist's concept of the heliospheric current sheet. The rotating Sun is located in the centre.

Ordinarily, the current sheet circles the Sun's equator like a wavy skirt around a ballerina's waist. But during the double north pole event of March 2000, the current sheet was radically altered: The waviness increased. Irregularities appeared. Its topology "morphed" from a ballerina's skirt to a giant seashell.

Interesting to a solar physicist, perhaps...

Ordinarily, the current sheet circles the Sun's equator like a wavy skirt around a ballerina's waist. But during the double north pole event of March 2000, the current sheet was radically altered: The waviness increased. Irregularities appeared. Its topology "morphed" from a ballerina's skirt to a giant seashell.

Interesting to a solar physicist, perhaps...

...but ordinary people should care about this, too. First because of energetic cosmic rays: The current sheet acts as a barrier to cosmic rays traveling through the heliosphere. Cosmic rays can't cross the sheet; instead they flow along it. The shape of the current sheet therefore determines how many cosmic rays strike Earth.

Space weather is another reason: As Earth orbits the Sun, it dips in and out of the undulating current sheet. On one side the Sun's magnetic field points north (toward the Sun), on the other side it points south (away from the Sun). South-pointing solar magnetic fields tend to cancel Earth's own magnetic field. Solar wind energy can then penetrate the local space around our planet and fuel geomagnetic storms.

Photo credit and copyright: LeRoy Zimmerman These auroras appeared over Alaska's Knik Valley during a strong geomagnetic storm on April 8, 2003.

Geomagnetic storms are both good and bad - bad because they can cause electronics on satellites to short circuit and power grids on Earth to fail; good because they spark auroras, which sky watchers enjoy. "If we could make an accurate daily map of the current sheet, then we could do a better job predicting the onset of these storms."