Comment on time conventions in the recordings of 1859

A variety of time conventions are used in the reports of the solar flare, magnetic disturbances, auroral displays and telegraph effects that occurred in August and September 1859. Civil time was determined by the longitude of the site and is the conventional day starting at midnight. However some reports used astronomical time where the 24 h day starts at noon. Many magnetic observatories around the world reported their data in “Gottingen time” either civil or astronomical. Particularly confusing is the term “Greenwich mean time” which is used in different reports meaning both ‘civil time’ and ‘astronomical time’ at Greenwich. Thus particular care is needed when comparing the observations made at different locations.