Terrella - encyclopedia article about Terrella.

Kristian Birkeland's magnetised terrella. In this experiment, he noted two spirals which he considered may be similar to that of spiral nebulae^[1] .

A terrella (meaning "little earth") is a small magnetised model ball representing the Earth, that is thought to have been invented by Englishman physician William Gilbert while investigating magnetism, and further developed 300 years later by the Norwegian scientist and explorer Kristian Birkeland, while investigating the aurora.

Terrellas had been used up until the late 20th century to attempt to simulate the Earth's magnetosphere, but have now been replaced by computer simulation.

William Gilbert's terrella

William Gilbert, the royal physician to Queen Elizabeth I, devoted much of his time, energy and resources to the study of the Earth's magnetism. It had been known for centuries that a freely suspended compass needle pointed north. Later investigators (including Christopher Columbus) found that direction deviated somewhat from true north, and Robert Norman showed the force on the needle was not horizontal but slanted into the Earth.

William Gilbert's explanation was that the Earth itself was a giant magnet, and he demonstrated this by creating a scale model of the magnetic Earth, a "terrella", a sphere formed out of a lodestone. Passing a small compass over the terrella, Gilbert demonstrated that a horizontal compass would point towards the magnetic pole, while a dip needle, balanced on a horizontal axis perpendicular to the magnetic one, indicated the proper "magnetic inclination" between the magnetic force and the horizontal direction. Gilbert later reported his findings in De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure, published in 1600.

Kristian Birkeland's terrella

Kristian Birkeland and his magnetized terrella experiment, which led him to surmise that charged particles interacting with the Earth's magnetic field, were the cause of the aurora^[2].

Kristian Birkeland was a Norwegian physicist who, around 1895, tried to explain why the lights of the polar aurora appeared only in regions centered at the magnetic poles.

He tried to simulate the effect using a "terrella," a sphere in a vacuum tank to which he directed beams of cathode rays, later identified as electrons, and found they indeed produced a glow in regions around the poles of the terrella. Because of residual gas in the chamber, the glow also outlined the path of the particles. Neither he nor his associate Carl Stoermer (who calculated such paths) could understand why the actual aurora avoided the area around the poles themselves.

We now know this relates to the origin of the auroral electrons, which is actually inside the Earth's Magnetosphere, the space region controlled by the Earth's magnetism. Birkeland believed the electrons came from the Sun, since large auroral outbursts were associated with sunspot activity.

Birkeland constructed several terrellas. One large terrella experiment was reconstructed in Tromsø, Norway.[1].

Other terrellas

Later terella experiments were performed by various scientists, studying various aspects of the interaction of the Earth's magnetic field in space. Brunberg and Dattner in Sweden, around 1950, used a terrella to simulate trajectories of particles in the Earth's field; today such simulations are conducted much more conveniently with computers. Podgorny in the Soviet Union, around 1972, built terrellas at which a flow of plasma was directed (simulating the solar wind), and Hafez u-Rahman at the University of California, Riverside conducted more realistic experiments around 1990. All such experiments are difficult to interpret, and are never able to scale all parameters to properly simulate the Earth's magnetosphere, which is why such experiments have now been completely replaced by computer simulations.

Footnotes

1. ^ Kristian Birkeland., The Norwegian Aurora Polaris Expedition 1902-1903, Section 2. Chapter VI (See page 678) Extract online
2. ^ Kristian Birkeland., The Norwegian Aurora Polaris Expedition 1902-1903

External links

NASA Educational Website on the Terrella

magnet is a material or object that produces a magnetic field. A "hard" or "permanent" magnet is one which stays magnetized for a long time, such as magnets often used in refrigerator doors.
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EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001. Their greatest hit, their debut single "time after time", peaked at #13 in the Oricon singles chart.
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Motto
Dieu et mon droit (French)
"God and my right"
Anthem
No official anthem specific to England — the anthem of the United Kingdom is "God Save the Queen".
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physician applies to a person who practices some type of medicine. Such medical practitioners are concerned with maintaining or restoring human health through the study, diagnosis and treatment of disease and injury, through both an area of knowledge
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William Gilbert, also known as Gilbard (Colchester, England, May 24, 1544 – London, England, November 30, 1603) was an English physician and a natural philosopher. He was an early Copernican, and passionately rejected both the prevailing Aristotelian philosophy and the
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Motto

Royal: Alt for Norge ("Everything for Norway")
1814 Eidsvoll oath: Enige og tro til Dovre faller
("United and faithful until the mountains of Dovre crumble")

Anthem
Ja, vi elsker

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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
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Auroras (or aurorae) [sing: aurora] are natural colored light displays, which are usually observed in the night sky, particularly in the polar zone. Some scientists therefore call them "polar auroras" (or "aurorae polaris").
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A magnetosphere is the region around an astronomical object in which phenomena are dominated or organized by its magnetic field. Earth is surrounded by a magnetosphere, as are the magnetized planets Jupiter, Saturn, Uranus and Neptune.
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Royal College of Physicians of London was the first medical institution in England to receive a Royal Charter. It was founded in 1518 and is one of the most active of all medical professional organisations.
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Elizabeth I (7 September 1533 – 24 March 1603) was Queen of England, France (in name only), and Ireland from 17 November 1558 until her death. She is sometimes referred to as The Virgin Queen, Gloriana, or Good Queen Bess
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Earth's magnetic field (and the surface magnetic field) is approximately a magnetic dipole, with one pole near the north pole (see Magnetic North Pole) and the other near the geographic south pole (see Magnetic South Pole).
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For other uses, see Compass (disambiguation).

COMPASS is an acronym for COMPrehensive ASSembler. COMPASS is a macro assembly language on Control Data Corporation's 3000 series, and on the 60-bit CDC 6000 series, 7600 and
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Christopher Columbus (1451 – May 20, 1506) was a navigator, colonizer and one of the first Europeans to explore the Americas after the Vikings. Though not the first to reach the Americas from Europe, Columbus' voyages led to general European awareness of the hemisphere and
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Robert Norman was a 16th century British mariner, compass builder, and hydrographer.

He is noted for his London publication in 1581 of The Newe Attractive, a pamphlet discussing the lodestone or magnet, as well as practical aspects of navigation.
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Lodestone or loadstone refers to either:
Magnetite, a magnetic mineral form of iron(II), iron(III) oxide Fe₃O₄, one of several iron oxides.
A piece of intensely magnetic magnetite that was used as an early form of magnetic compass.

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Dip circles are used to measure the angle between the horizon and the Earth's magnetic field (the dip angle). They were used in navigation, mining and prospecting as well as for the demonstration and study of magnetism.

Shen Kuo first discovered dip angle in 11th century.
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De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on That Great Magnet the Earth) is a scientific work published in 1600 by the English physician and scientist William Gilbert and also by his partner
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15th century - 16th century - 17th century
1570s 1580s 1590s - 1600s - 1610s 1620s 1630s
1597 1598 1599 - 1600 - 1601 1602 1603

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Subjects: Archaeology - Architecture -
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18th century - 19th century - 20th century
1860s 1870s 1880s - 1890s - 1900s 1910s 1920s
1892 1893 1894 - 1895 - 1896 1897 1898

:
Subjects: Archaeology - Architecture -
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Cathode rays are streams of electrons observed in vacuum tubes, i.e. evacuated glass tubes that are equipped with at least two electrodes, a cathode (negative electrode) and an anode (positive electrode) in a configuration known as a diode.
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Electron

Theoretical estimates of the electron density for the first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density
Composition: Elementary particle
Family: Fermion
Group: Lepton
Generation: First
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Fredrik Carl Mülertz Størmer (1874 – 1957) was a Norwegian mathematician and physicist who studied the movement of charged particles in the magnetosphere and the formation of aurorae.
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The Sun

Observation data
Mean distance
from Earth 1.49610¹¹ m
(8.31 min at light speed)
Visual brightness (V) −26.74^m ^[1]
Absolute magnitude 4.
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sunspot is a region on the Sun's surface (photosphere) that is marked by a lower temperature than its surroundings and has intense magnetic activity, which inhibits convection, forming areas of low surface temperature.
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Tromsø (help info ) (Romsa in Northern Sami, nominative case, Tromssa in Finnish) is a city and municipality in the county of Troms, Norway.
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