One of the earliest astronomers to ever produce a complete map of the moon, Johann Heinrich von Mädler’s four-quadrant representation of the lunar surface remained an unsurpassed early representation of Earth’s lonely natural satellite for almost half a century.
Known as the Mappa Selenographica, Mädler laboriously poured over the moon on an almost nightly basis through his refractor telescope, not only observing and mapping lunar features but also producing measurements of its various features that included craters and his estimates regarding the height of lunar peaks. Mädler’s collaborations with Berlin banker and fellow astronomer Wilhelm Wolff Beer also resulted in the earliest charts cataloging the surface of Mars.
While Mädler’s contributions to early astronomy remain of significance today, he is also remembered for one of his curious observations involving the planet Venus. Although documented elsewhere in historical accounts detailing observations of the planet, the anomalous occurrence has since become so closely associated with Mädler that astronomers have given it the apt title of “The Mädler Phenomenon.”
During the spring of 1833, prior even to the publication of his Mappa Selenogra, Mädler had been observing Venus’s approach of an inferior conjunction, a period where both Mercury and Venus are positioned on the same side of the sun. At the time, Mädler was observing Venus through a refractor telescope and had noticed a few minor irregularities in the planet’s appearance which may have been influenced by the planet’s position relative to the Sun. However, Mädler might never have guessed how unusual the planet’s appearance would become in the days ahead.
On April 7, as Mädler trained his telescope on Venus, he was surprised by a sudden, significant change in the planet’s appearance. Mädler was able to see long rays or “brushes” of light extending off to the side of the planet, giving it an appearance so curious that had he not known otherwise, the astronomer might have mistaken Earth’s neighbor for being a comet. The observation had not been fleeting either; over the course of the next 20 hours, Mädler was able to continuously observe these unusual beams of luminosity that gave Venus a fan-tailed appearance.
What might have been the cause of this peculiar display? Considering whether the problem had been originating with the telescope itself, Mädler made adjustments but could find no change in the appearance of Venus with adjustments in magnification, angle, or rotation. Mädler also conducted tests to determine if the ghostly rays emanating from Venus could be an illusion, but to no avail; whatever had been producing this curious spectacle appeared to be a real light phenomenon, the likes of which the astronomer had never witnessed before.
The debate has continued as to what might have been the source of the mystery, although not everyone was convinced by Mädler’s account. In his Celestial Objects, the Reverend T.W. Webb discussed Mädler’s observation, noting that “it is an instructive instance of the oversights which may be incidental even to great philosophers, that it never occurred to [Mädler] to try another telescope.” Of the opposite perspective, R. Baum writing in the Journal of the British Astronomical Association would note in 1988 that “it is difficult to credit the greasy finger hypothesis advanced by one modern astronomer without charging Mädler with gross incompetence, a rather unlikely possibility given his later success.” Baum, however, offered his own take on what could account for the phenomena observed by Mädler, pointing to atmospheric conditions described in the weather diary of John Gadbury as being able to account for the unusual observation.
The likely solution would appear to have been some variety of halo or another effect similar to the atmospheric optical phenomena known as a light pillar. Nonetheless, Mädler’s reputation as a detailed chronicler of astronomical data resulted in the phenomena in question bearing his namesake to this day, being recognized as one of the many curious footnotes in the history of human observation of our planetary neighbors.