By Tim Carr
At the western edge of the Sea of Storms on the Moon, there is a crater named Hevel. Seventy miles wide, its walls are 6,000 ft high in places and a good telescope will show a fine system of rilles on the crater floor. It is named after a German astronomer called Johannes Hevel (or Hewelcke) who was born in Danzig in 1611.
By day he was a successful brewer and member of the city council but his nights were spent in his rooftop observatory, which was perhaps the best in Europe, using the telescopes he himself made to map the Moon in greater detail than ever before.
The Moon had been studied before of course, most notably by Galileo but the great italian’s drawings were crude compared to the ones Hevelius made. In 1647, he published the Selenographia – an atlas of the Moon based on observations made over a decade. He was the first person to realize that the dark features were low-lying areas which he called maria (seas) and that the brighter ones were uplands. We now know that the maria are as dry as a bone (much dryer, in fact) but he was right about the elevations and measured the heights of the lunar mountains quite accurately. The names of the major plains and mountains he used have survived to this day.
As well as the Moon, he also observed the phases of Mercury, worked out a close value for the rotation of the Sun and discovered what he called ‘faculae’ – the bright regions on the surface of the sun associated with sunspots.
As if all that wasn’t enough, he discovered four comets and published two books on the subject. Like the Italian mathematician Giovanni Borelli, he thought that comets went around the Sun in a parabolic path. In 1657, he began what was to be the most comprehensive mapping of the sky yet undertaken but in 1679 his observatory burned down.
Nevertheless he could still publish ‘Uranographia‘ containing 1500 star co-ordinates. Hevelius did not use his telescopes at all for this work, despite such luminaries as Edmund Halley encouraging him to do so. Even half a century after the invention of the telescope, many astronomers felt that they could not trust it to produce accurate enough images for something as demanding as a map of the stars.
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