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An analysis of the sunspot observations made by Hevelius during 1642-1645 ispresented. These records are the only systematic sunspot observations justbefore the Maunder Minimum. We have studied different phenomena meticulouslyrecorded by Hevelius after translating the original Latin texts. We re-evaluatethe observations of sunspot groups by Hevelius during this period and obtain anaverage value 7% greater than that calculated from his observations given inthe current group database. Furthermore, the average of the active day fractionobtained in this work from Hevelius' records previous to the Maunder Minimum issignificantly greater than the solar activity level obtained from Hevelius'sunspot observations made during the Maunder Minimum (70% vs. 30%). We alsopresent the butterfly diagram obtained from the sunspot positions recorded byHevelius for the period 1642-1645. It can be seen that no hemispheric asymmetryexists during this interval, in contrast with the Maunder Minimum. Heveliusnoted a ~3-month period that appeared to lack sunspots in early 1645 that gavethe first hint of the impending Maunder Minimum. Recent studies claim that theMaunder Minimum was not a grand minimum period speculating that astronomers ofthat time, due to the Aristotelian ideas, did not record all sunspots that theyobserved, producing thus an underestimation of the solar activity level.However, we show the good quality of the sunspot records made by Heveliusindicates that his reports of sunspots were true to the observations.

Sunspot characteristics at the onset of the Maunder Minimum based on the observations of Hevelius