AURORAL OBSERVATIONS ON AD 1770 SEPTEMBER 16 - THE EARLIEST KNOWN CONJUGATE SIGHTINGS

Observations of the aurora australis on the night of AD 1770 September 16 have been recorded in the journals of Joseph Banks and Sydney Park inson, written on board HMS Endeavour during the first voyage of Capta in James Cook to Australia. Both descriptions of the aurora australis refer to a red light or glow in the southern sky, accompanied by rays, or stripes, of a brighter coloured light extending directly upwards. Observations of the aurora borealis on the same night have been record ed in Chinese provincial histories, which refer to auroral displays in the northern sky. The Chinese provincial histories also indicate that the aurora borealis was observed each night during the interval 1770 September 16-18, and include several references to a red light in the north or north-west. Japanese histories indicate that red auroral disp lays were also observed from several places in Japan on the night of 1 770 September 17. Assuming that the red light seen in both hemispheres was predominantly 630-nm ('red line') emission from excited atomic ox ygen, the magnetic field model of Bloxham & Jackson, valid for the int erval 1690-1840, is used to show that these early contemporaneous auro ral descriptions are consistent with conjugate auroral observations du ring an intense geomagnetic storm. These observations provide the earl iest example yet known of conjugate auroral sightings.