Abstract
Low-latitude auroras are extremely rare. In this work, we study the low-latitude aurora observed on November 14 and 15, 1789. Before this one, several auroras had been studied in the world but no one of low-latitude. As far as we know, this was the first to be studied observationally, physically and mathematically: two explanations were proposed, aurora’s height and overhead were measured, one aurora treatise were published, its observation was predicted in other regions, and, for the first time, an aurora was reproduced in a laboratory. These analyses were carried out by three Mexican scientists, Antonio de León y Gama, José Antonio Alzate and Francisco Dimas Rangel. We used these Eighteenth century works to estimate some parameters of the 1789 aurora. We calculated the height and we confirmed that León y Gama’s value was determined correctly for low latitude auroras, in the range between 460 and 680 km. We also determined the position of the auroral oval, and we found it was almost circular with a radius of approximately 4786 km; probably this aurora manifested along the entire length of the auroral oval, or at least in the arc of the circle between America and Europe. We estimated the geomagnetic latitude of the auroral oval (overhead points) at 47°N (43° from the geomagnetic north pole). We determined, as well, the geomagnetic latitude of the southernmost places where it was seen at ~34° (56° from the geomagnetic north pole). Our result on the relationship between sub-zenith point (overhead) and southernmost point is 30°/17° (geographic latitude), the lowest reported at that time.
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