Editing Terrella (section)

{{Short description|Device that simulates Earth's magnetic field}}
[[File:Birkeland-terrella-spiral-nebula.jpg|thumb|Kristian Birkeland's magnetised terrella. In this experiment, he noted two spirals which he considered may be similar to that of [[spiral nebula]]e.<ref name=NAPE>{{cite book |last=Birkeland|first=Kristian |title=The Norwegian Aurora Polaris Expedition 1902-1903 |year=1908–1913 |publisher=H. [[Aschehoug]] & Co |location=New York and Christiania (now Oslo) |url=https://archive.org/details/norwegianaurorap01chririch|via=[[archive.org]]}} out-of-print, full text online</ref><ref group=note>Section 2, Chapter VI, p. 678</ref>]]
[[File:Aurora borealis in a lab dsc04517.jpg|thumb|An example of an active terrella]]

A '''terrella''' ({{langnf|la||little earth}}) is a small [[magnet]]ised model ball representing the [[Earth]], that is thought to have been invented by the English physician [[William Gilbert (astronomer)|William Gilbert]] while investigating [[magnetism]], and further developed 300 years later by the Norwegian scientist and explorer [[Kristian Birkeland]], while investigating the [[polar aurora|aurora]].

Terrellas have been used until the late 20th century to attempt to simulate the Earth's [[magnetosphere]], but have now been replaced by computer simulations.