Kristian Birkeland

Kristian Birkeland (December 13, 1867 - June 15, 1917) was born in Christiania (Oslo today) and wrote his first scientific paper at the age of 18. He organized several expeditions to Norway's high-latitude regions where he established a network of observatories under the auroral regions to collect magnetic field data. The results of the Norwegian Polar Expedition conducted from 1899 to 1900 contained the first determination of the global pattern of electric currents in the polar region from ground magnetic field measurements. The discovery of X-rays inspired Birkeland to develop vacuum chambers to study the influence of cathode rays on magnets. An example of one of his experiments is depicted on the left front of the bank note. It shows a magnetized terrella, simulating the Earth, suspended in an evacuated box. Birkeland noticed that an electron beam directed toward the terrella was guided toward the magnetic poles and produced rings of light around the poles and concluded that the aurora could be produced in a similar way. He developed a theory in which energetic electrons were ejected from sunspots on the solar surface, directed to the Earth, and guided to the Earth's polar regions by the geomagnetic field where they produced the visible aurora. Birkeland was nominated for the Nobel Prize no less than seven times.

Vision of field-aligned currents stirs controversy

Birkeland suggested that polar electric currents -- today referred to as auroral electrojets -- were connected to a system of currents that flowed along geomagnetic field lines into and away from the polar region. He provided a diagram of field-aligned currents in his book, The Norwegian Aurora Polaris Expedition 1902-1903. This diagram is reproduced on the back of the bank note in the lower right corner. This book contains chapters on magnetic storms on the Earth and their relationship to the Sun, the origin of the Sun itself, Halley's comet, and the rings of Saturn. Birkeland's vision of field-aligned currents became the source of a controversy that continued for a quarter of a century, because their existence could not be confirmed from ground-based measurements alone.

Related Topics:
Polar electric currents - Earth - Sun - Halley's comet - Saturn

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The absolute proof of Birkeland's field-aligned currents could only come from observations made above the ionosphere with satellites. A magnetometer onboard a U.S. Navy navigation satellite launched in 1963 observed magnetic disturbances on nearly every pass over the high-latitude regions of the Earth.

Related Topics:
Ionosphere - Satellite - Magnetometer - 1963

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The magnetic disturbances were originally interpreted as hydromagnetic waves, but it was soon realized that they were due to field-aligned or Birkeland currents. The first complete map of the statistical location of Birkeland currents in the Earth's polar region was developed in 1974 by A.J. Zmuda and J.C. Armstrong and refined in 1976 by T. Iijima and T.A. Potemra from satellite-borne magnetic field observations. The ring encircling the magnetic pole depicted on the back of the bank note is similar to the patterns of Birkeland and current derived from satellites.

Related Topics:
Birkeland current - A.J. Zmuda - J.C. Armstrong - T. Iijima - T.A. Potemra

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Birkeland's face appears a second time in a watermark in the blank space above the drawing of the Terrella, and his rudimentary magnetosphere appears on the back but is only visible under ultraviolet light.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The Norwegian 200 krones note is a handsome example of modern currency, and it is a fine tribute to one of the world's greatest space physicists.

Related Topics:
Norwegian 200 krones note - Space physicists

~ ~ ~ ~ ~ ~ ~ ~ ~ ~