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From a letter by Leonhard Euler some speculations on the height of auroas in the atmosphere can be derived.
Based on visual noctilucent cloud data, the effect of the autumn transition of winds in the mesosphere is investigated. Following the autumnal transition of the mesospheric winds no noctilucent clouds were observed. The higher temperature of the winter mesosphere can be physically explain the fact that no noctilucent clouds occur during winter of the Northern Hemisphere. Accordingly, noctilucent clouds only occur on the typical summer mesosphere related to the low temperature there and due to the stable condition of the then mesospheric region.
The development of the great aurora of January 18, 1770 has been discussed in a fundamental paper by Silberschlag (1770) and other authors. The aurora was observed in middle and low latitudes and in Northern latitude. In Central Europe it displayed all typical auroral forms, including the Corona.
It is shown that during the Maunder Minimum auroras were observed frequently and the solar cycle was regular.
A new interpretation of celestial phenomena became apparent after the appearance of the great aurora of March 1716. The philosopher Wolff presented a general lecture to the public in which he explained the aurora as a normal celestial phenomenon.
The paper deals with the letters written by Aurora Formentini to his husband, Ádám Batthyány in the 1630s. The documents, which are of rather low historical interest, may be analysed in respect to their language. Nobody knows what the mother tongue of the Countess in fact was. What is known is that she was born in Gorizia (Friuli), was educated in Vienna and married in Hungary. Although she was educated at the emperor's court, her language use is far from any standard grammatical canon.
A compilation of German auroral observation data for 1949-1964 is given. The observations are analysed with respect to the K p-index and seasonal variation. The appendix contains a full list of these observations.
