Did Lomonosov see the Venusian atmosphere?

Vladimir Shiltsev (Physics Today, February 2012, page 40 ) properly credits Mikhail Lomonosov with a wide range of scientific achievements. But we have been corresponding with Shiltsev for some months about our realization ¹ that Lomonosov did not discover the atmosphere of Venus. One of us (Pasachoff) analyzed spacecraft observations of the Cytherean atmosphere at the 2004 transit of Venus, ² and we realized that what Lomonosov reported did not match actual atmospheric observations. NASA’s Transition Region and Coronal Explorer spacecraft detected Venus’s atmosphere for about 20 minutes as Venus’s silhouette entered the Sun’s limb, and again for the first 20 minutes of its exit from the solar disk. Lomonosov saw only a bulge of light—shown in figure 4a of Shiltsev’s article—and a brief flash of light. We think that what he saw was an artifact of his relatively primitive and small telescope rather than the aureole that is sunlight refracted toward Earth by Venus’s atmosphere. Our conclusions were reinforced by observations made during the 2012 transit of Venus.

Lomonosov wrote, quoted here from a translation made for us, “I watched with keen attention for the ingress of the trailing limb of Venus, which, it seemed, had not yet taken place, for there seemed to be a small segment not yet entered upon the Sun. However, there suddenly appeared between the trailing limb of Venus and the following [solar] limb a hair-thin luminous sliver. The time that separated the two appearances was not more than a second” (reference , page 5). But the actual aureole is produced by the refraction of sunlight in the Venusian atmosphere, and it is much too thin and faint for 18th-century observers to have seen it with the instruments available to them and from their low-altitude locations. Further, the bulge Lomonosov reported was probably an artifact that resulted from the blurring of the edge between Venus’s dark disk and the bright solar limb on either side of it.

Like most scientists of his time, Lomonosov expected that all planets had life on them and therefore needed atmospheres to nurture that life, so he was inclined to report that he had discovered an atmosphere. Most of his article was philosophical in nature. The fact that he didn’t actually have observations to back the correct conclusion does not diminish his achievement as one of the most important scientists of his time, and it would only dim his luster to credit him with discoveries that he didn’t make.