Given the existing technology at the time, did Johannes Hevelius (1611-1687) able to know more about the Moon in comparison to his astronomy contemporaries?
By: Ringo Bones
Some astronomers think that we only managed to know more about the Moon than Johannes Hevelius did when we had the ability to send robotic spacecraft and manned exploration of the Moon, but is there some truth to this? Even though it was Galileo who first documented the Moon’s topography as seen from his first telescope back in 1610. It was Johannes Hevelius, a notable Polish astronomer born in January 28, 1611 that from his crowded rooftop in Danzig laden with his custom built telescopes – where he gained the fame as the pioneer of Lunar topography a few years later. Hevelius also studied distant celestial objects, but learned little because of dust and other disturbances in the atmosphere over Poland despite using an aerial telescope of his own design that’s 150 feet (46-meter) long – equal to the height of a modern 12-story building.
In collaboration with his wife Elizabeth, they charted the Lunar landscape then published their descriptions in Selenographia back in 1647. During his extensive studies of the Moon, Hevelius got curious of the fact that 59% of the Moon’s surface visible from Earth. During his time, the period between new Moons was already measured with a fair degree of accuracy. And the fact that the same face is always turned toward the Earth with only minor wobbling – the extra 9% of the Moon’s surface seen from Earth – was noted although not explained. The modern explanation is in part that the Moon is not a perfectly symmetrical spheroid. The Moon has a massive bulge, which the Earth’s gravitation attracts like a plumb bob, thus keeping the same hemisphere towards the Earth. With such detailed observations of the Moon, Johannes Hevelus’ contribution to modern selenology was indeed indispensable.
During his lifetime, Johannes Hevelius was also credited for discovering four comets and was noted for his suggestion that the comets revolved around the Sun in a parabola. And his observations on comets were published in Prodromus Commeticus in 1665 and Cometographia in 1688. Hevelius also listed 1,564 stars and in 1661 became the second person on Earth to witness the transit of Mercury – i.e. the planet Mercury moving across the face of the Sun as seen from Earth. Coincidentally, he passed away during his birthday on 1687.