Lomonosov vs. Wargentin & Mallet vs. Silberschlag

Various key reports from the 1761 Transit of Venus

Translated from German into English by Daniel Fischer on 23/24 June and 8 July 2012

Translation of "Apparition of Venus in front of the Sun observed at the Imperial Academy of Sciences in St. Petersburg on 26 May 1761 # Translated from Russian" beginning at the top of (PDF) page 10 [before that the contact timings and diameter measurements of Venus by other astronomers are discussed, after that only lengthy religious arguments follow]; for the illustrations refer to PDF page 8 of this direct translation from Russian:

Apart from these precise astronomical observations also the Collegien-Rath [an academic title] and professor Lomonosov also observed the celestial event in his house [= institute?] predominantly for physical purposes. He had a telescope of 4 1/2 foot with two lenses [that's how I translate "Gläser" = glasses]. For this telescope glasses only thinly coated were used, since he wanted to observe only the beginning and end [of the transit] and use all of his visual power for that while he wanted to rest his eyes in between. [Does that mean that he deliberately employed filters of insufficient density for the ingress/egrees observations? Yikes!]

Having waited for the ingress of Venus some forty minutes longer that it should have happened according to the ephemeris, the limb of the Sun where ingress should take place did not look as bright as before but appeared somewhat dimmed ["trüb" could also mean ill defined here]; before it had appeared completely clean and clear, see B. fig. 1. Since no real blackness was visible yet, he concluded that his tired eye was to blame and looked away from the tube. Some seconds later he looked into the tube again and noted that at the location which has looked so dimmed just before there was now a really clear black arc of Venus in ingress. With great diligence he then observed the ingress of the following limb of Venus; it had, as it seemed, not quite touched the limb of the Sun yet, but it appeared as if a small part of Venus was still outside the limb of the Sun. But all of a sudden between the following limb of Venus and and the Sun's limb a very bright light appeared, as wide as a hair, which split Venus off from the limb of the Sun, so that both [events] happened in no more than one second.

When Venus during egress from the Sun approached the solar limb and was - roughly estimated - one tenth of its diameter from the limb of the Sun, a bump, A fig. 1, appeared at the Sun's limb which grew ever more visible the closer Venus came to its egress fig. 3 and 4. L S is the limb of the Sun and m m the bump on the same in front of Venus. In one instance this apparent hill vanished and immediately Venus was missing a small but as in fig. 5 n n very obvious part of its limb.

Before the complete egress of this planet from the Sun, i.e. when touching the Sun from the outside, this limb also turned somewhat unclear and dim.

It was also noted that as soon as Venus moved out of the the [optical] axis if the tube and approached the edge of the aperture, immediately refraction caused colors, and the limb [of Venus] became all the more unclear as it moved from the axis X. For this reason the tube was always placed in a way that the planet was constantly in the center of the tube's aperture, so that its limb was alwas visible clearly and without colors.

From these observations Mr. Rath Lomonosov concludes that the planet Venus is surrounded by a significant atmophere [he actually says "Dunstkreis" = haze circle], not larger but as large as our Earth's atmosphere. Because the decrease in clearness at the bright solar limb B even before the true ingress of Venus demonstrates the ingress of Venus' atmosphere into the Sun. This is explained in figure 6. L S [is] the limb of the Sun, P P part of the atmosphere of Venus. During egress an outer bump on the Sun's limb appeared. This can only mean that the Sun's rays were refracted in Venus' atmosphere. L P [is] the end of the diameter [unclear what this means] of the visible solar surface, (fig. 7); s c h the body of Venus; m n n its atmosphere. L O is the light ray as it would hit the observer's eye in a straight line after grazing Venus' body in the case of no atmosphere present. As soon as there is an atmosphere, however, the ray from the Sun's limb L d must refract in d, run against the perpendicular til h, refract again and go to the observer's eye in O. Now it is known from optics that the eye perceives an object in the direction from which its ray hits it; thus the solar limb L must appear in R after being refracted in the straight line O R, and for this reason the superfluous space LR on the solar limb at Venus egress causes a bump in front of its leading limb [the grammar is really convoluted here, but so it makes sense].

Translation of "The distance of the Sun from the Earth, derived from the Transit of Venus of 1761" by J. F. Encke from 1822, from page 101 to page 104 [embedded in a lengthy discussion of how to define and properly observe the inner contacts]:

One minute before interior ingress it seemed to Wargentin as if Venus was completely inside the Sun. He saw her complete round shape clearly, although with a weaker glow on the outside, where Venus would enter last. At first he believed that glow was nothing but the glare of the Sun surrounding the planet from all sides; since that glare however didn't increase as quickly as he expected, he looked intently until he saw another stronger and livelier glare suddenly surrounding the planet. The pointy opposing cusps of the Sun, which before had grasped Venus on the outermost side converged and included her completely.

As Venus approached egress Wargentin saw that Venus made an opening in the solar limb as a fine thread of light, which before had been going around the outermost limb of Venus approaching egress, tore apart in the middle in an instant, and its ends separated markedly. The light now lacking was not the foreign glare that had been seen before complete ingress and also later during egress but the direct light from the Sun; otherwise it couldn't have disappeared so fast and clearly. With a stronger telescope Klingenstierna saw the light thread burst three seconds later.

Now Wargentin let his eye rest until Venus had left the Sun up to one quarter, and now it appeared to him as if he saw a faint glow, like during ingress, around the limb of Venus which had already left the Sun. It looked like a narrow ring outside the Sun which matched the part of Venus on the Sun and kind of completed it. The lower and more southern part of the ring seemed brighter and more obvious than the upper one. Wargentin had doubts at times if he saw something real, because Klingenstierna couldn't notice anything, and after looking for a while for Wargentin the ring got weaker; always however when he let his eye rest he saw it very clearly again; it seemed to him to come from Venus' atmosphere. As complete egress approached Wargentin saw a black dot from Venus at the Sun's edge for 10 to 12 seconds before it disappeared.

Somewhat different is the description of the phenomenon in Upsala. Here Venus had a glow around it as well when she had entered the Sun only by three quarters. She then seemed to enter in her totality and had the same roundness, except where she was closest to the Sun's limb. There the black Venus appeared elongated, as if a bump stretched to the solar limb like a drop of water. Without leaving the edge Venus moved a bit into the Sun, connected to its limb by a black belt that got narrower all the time until it tore apart in the middle, with one end retreating to the solar limb, the other to the dark Venus which H. Mallet now saw standing inside the Sun by the 6th to 8th part of its diameter.

During egress the limb of the Sun seemed at 9h 27' 55" W.Z. so close to the Sun's limb that it would have touched it if the Sun's limb would not have warped and made a bump at the border of the Sun. This lasted some seconds, but the impression faded by and by, so that Mallet could not notice the precise moment when the solar limb opened, which he could time only to within two seconds. At 9h 28' 1" there was still a very weak glow of the narrow rim of the Sun. At 9h 28' 3" it was opened so strongly that Mallet imagined that Venus had already left the Sun a little bit. One could see the opposing cups of the Sun, and a glow surrounded Venus and showed her round shape clearly.

When Venus was about to leave the Sun it appeared to Mallet as if she was clinging more to the Sun as was appropriate for her round shape; in the end he noticed however that the round limb of Venus ended in an angle that was at first obtuse but getting ever more acute; at 46' 23" is was larger as a right angle, at 29" is was as acute as a rapier point and then left the Sun in an instant.

Translation of "The perceived Transit of Venus through the Sun" by G. C. Silberschlag from 13 June 1761 [following a general description and contact timings]:

And finally one should note that, as Venus was about to touch the limb of the Sun from the interior, the latter bulged above its circle in such an arc that it was completely parallel to the limb of Venus. Experts will consider this phenomenon unanimously as an effect of of Venus' atmosphere, in which certainly a strong refraction of light rays must take place. A remarkable circumstance! For now the existence of the atmosphere of Venus, which until now could only be claimed by analogy, has been comfirmed fully by observation.

For comparision: visual reports from the 2012 ToV

Translation of The Transit of Venus on the Morning of 6 June 2012 by B. Schatzmann in a Sternkieker special digital ToV edition, p. 29; he observed with a 9-cm refractor and an ND 3.8 - i.e. unusually bright - filter; this follows a description of 3rd contact approaching:

And when they touched? Til the last moment, there is a thin bridge of light, no black drop like in historical illustrations or descriptions. [...] And then: Indeed, on the rim of Venus, now moving beyond the solar limb, the atmosphere of Venus appears as a thin line, delineating the sphere [of Venus]. At first as a complete arc, then more asymmetrical as a small arc segment more in the East of the Venus sphere [...].

Translation of Transit of Venus on the corn field by M. Ettling in a Sternkieker special digital ToV edition, p. 33; he observed with an 8-cm refractor and an ND 5 - i.e. of recommended density - filter:

As Venus had moved beyond the limb of the Sun, approximately in the interval 30 to 90 seconds after third contact, I could spot, in the moments of best seeing, an extremely thin bridge of light at the rim of Venus. The Ring of Lomonosov! It was really hard to see, not obvious at all. But I could fixate it for moments, now and then, as I said during about a minute. A small, ringlike impression of an arc of light, very faint and extremely thin, but clearly there.