Auroras observed in Portugal in late 18th century obtained from printed and manuscript meteorological observations
Vaquero J.M., Trigo R.M.
Solar Physics, 231, 157-165, DOI: 10.1007/s11207-005-1583-7
We present a new catalogue of observations of the aurora borealis at Lisbon, i.e., at lowlatitudes, in the late 18th century by Jacob Prętorius and Henrique Schulze, two German artillery officers. Dates of 18 auroras compiled by Prętorius and Schulze are compared with those published in other catalogues for that period. The number of annual auroras observed by the two Germans is then compared with two indices of solar activity showing a very good level of consistency between all time series. Finally, we have assessed the number of auroras observed taking into consideration the phase of the lunar cycle and the geomagnetic latitude of Lisbon.