Abstract
Observation of auroras at low latitudes is an extremely rare event typically associated with major magnetic storms due to intense Earth-directed Coronal Mass Ejections. Since these energetic events represent one of the most important components of space weather, their study is of paramount importance to understand the Sun-Earth connection. Due to the rarity of these events, being able to access all available information for the few cases studied is equally important. Especially if we refer to historical periods in which current accurate observations from ground-based instruments or space were not available. Certainly, among these events, we must include the great aurora of February 4, 1872. An event whose effects have been observed in different regions of the Earth. What we could consider today a global event, especially for its effects on the communication systems of the time, such as the transatlantic cable that allowed a connection between the United States and Europe since 1866. In this paper, we describe the main results of the observations and studies carried out by Angelo Secchi at the Observatory of the Roman College and described in hisMemoria sull’Aurora Elettrica del 4 Febbraio 1872for the Notes of the Pontifical Academy of new Lincei. This note is extremely modern both in its multi-instrumental approach to the study of these phenomena and in its association between solar-terrestrial connection and technological infrastructures on the Earth. The Secchi’s note definitely represents the first example of analysis and study of an event on a global scale, such as the Atlantic cable, affecting the Earth. What we nowadays call an extreme space weather event.
Highlights
Rapid growth in the realization of heliophysical ground-based instrument networks and space missions has contributed to an awareness of the complexity of the SunEarth system and of the possible impact that extreme space weather events can have on our technological society
As we reported in the previous paragraph, the great aurora of February 4, 1872 was one, if not the most intense geomagnetic event of solar origin of the last 200 years
The Secchi’s note on February 18, 1872 (Secchi, 1872) opens with these words: the superb electric aurora that we witnessed on the 4th of this month, is so extraordinary, for our climates, that it deserves to be handed down to posterity with all the particularities that were reported during his appearance; and this is more necessary since various important facts for the theory of the phenomenon have emerged
Summary
Rapid growth in the realization of heliophysical ground-based instrument networks and space missions has contributed to an awareness of the complexity of the SunEarth system and of the possible impact that extreme space weather events can have on our technological society. Uncommon extreme events, such as those associated with the major auroras of the last two hundred years, represent case studies of capital scientific and historical interest. It is extremely interesting, both from a historical and scientific point of view, to present Secchi’s note which for the first time connects, in a multi-instrument study, solar sources, auroral effects, and the failures of technological infrastructures, like the Atlantic rope, on a planetary scale
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