Vladimir Shiltsev, Igor Nesterenko, and Randall Rosenfeld call Mikhail Lomonosov a great Russian polymath (Quick Study, Physics Today, February 2013, page 64), and indeed, he is credited with many important discoveries. In astronomy, however, he is almost exclusively remembered for his putative “discovery” of the atmosphere of Venus at the transit of 1761.
Shiltsev, who is a distinguished physicist and director of the Accelerator Physics Center at Fermilab but not an astronomer, and several colleagues attempted to “experimentally rerun” Lomonosov’s discovery at the June 2012 transit. They equipped themselves with 18th-century instruments similar but not identical to the one Lomonosov used (which seems not to have survived) and sought to make out the luminous arc that fringes the silhouette of Venus edging onto the Sun. This arc, or aureole, is produced by refraction of sunlight in the planet’s atmosphere. Meanwhile, at the same transit, Rosenfeld and colleagues in Saskatchewan made observations using modern doublet lenses and concluded that the aureole could, in principle, be detected with a 50-mm lens, the type Lomonosov most likely used. Putting all this together, Shiltsev, Nesterenko, and Rosenfeld conclude that Lomonosov must have seen the arc and on that basis correctly deduced the existence of the atmosphere.
We disagree with that conclusion. Such an experimental rerunning of Lomonosov’s observations shows only that he could have made out the arc, not that he did. And we don’t think he did, for the following reasons.
Repeating a historic visual observation with a telescope is not exactly analogous to repeating experiments in physics, such as those of Hans Christian Oersted with electricity and magnetism, say, or Robert Boyle’s with an air pump. In those experiments, all the significant experimental conditions can be controlled for and thus duplicated. But in astronomical observations, it is difficult to achieve the same control, since the conditions include not only the aperture and type of the telescope but also atmospheric conditions and subjective factors such as the observer’s preconceptions and beliefs.
Lomonosov held, as did many scholars of his day, that all the other planets were inhabited. Accordingly, Venus must have a considerable atmosphere to support its inhabitants. He therefore would have seized on possible blurring or other distortions as evidence of the existence of an atmosphere.
To establish Lomonosov’s claim as a discovery and not merely a plausible surmise, it is not enough to show that a modern observer with smallish equipment can see the aureole and that Lomonosov must therefore have done so. One must show, as Rosenfeld stresses,1 that “careful analysis of observational records”—and that alone—can explain what Lomonosov saw. We took that approach and tried to do this by translating Lomonosov’s documents and reviewing his drawings.2 Importantly, he himself never referred to an “arc,” but rather to a “bump” or “blister.” Furthermore, he said he saw a “sliver” for one second—another possible atmospheric sighting—but at the recent transit, we could discern the atmosphere for many minutes through small telescopes, one of us (Sheehan) from Flagstaff, Arizona, and the other (Pasachoff) from Haleakala, Hawaii.
A careful analysis of Lomonosov’s writings and drawings shows that what he observed, at least as he recorded it, did not resemble the actual aureole as recorded in later ground- and satellite-based observations. Shiltsev’s drawing (figure 1c in the Quick Study) shows what appears to be a classical “black drop” bordered by a distorted piece of solar limb, which he identifies with Lomonosov’s bump shown in figure 1a. Taken at face value, that analogy suggests that Lomonosov was actually recording a variant of the black-drop effect, which turns out to have nothing to do with Venus’s atmosphere.3,4 The thickish bump is only superficially similar to the hairline arc in figure 1b, Alexandre Koukarine’s drawing, which correctly depicts the aureole.
Although Lomonosov may have assumed that Venus has an atmosphere, then set out to prove it by making direct observations during the transit, and then calculated the atmosphere’s thickness based on its potential refracting effects, we remain unconvinced that he truly observed any of the actual phenomena—such as the aureole—on which the proof that Venus has an atmosphere now securely rests.
