A couple of years ago, I was sent pictures of the front and rear side of an old, early nineteenth century’s playing card by Gejus van Diggele, who is a collector of antique playing cards. These cards sometimes have unusual features, like notes written on the back of the card. These notes may vary from love letters to scientific records.
For years, the note on the back of this particular seven of hearts puzzled Gejus: what was the note about? Apparently, it was a record of some kind of astronomical observation. When Venus transited the sun in 2004, the images of a small, black dot on the sun’s disk appearing in newspapers, magazines and on the Internet were reminiscent of the old card’s drawing. So, Gejus contacted me to see if I could help to solve the mystery.
The text is in French and reads as follows: “Le 16 Juin 1835 à 3 h un seul point presque invisible dans la vapeur blanche. Le matin il soit plus sensible.” Translated: “On June 16 1835 at 3 h a single point almost invisible through the white haze. In the morning it was more sensible.”
Although the sketch accompanying the note does remind us of a planetary transit, the date clearly shows that it cannot be about an inferior planet passing in front of the sun’s disk. Transits of Venus always occur in early June or December, and Mercury always transits the sun in May or November. Then, might this note be a record of a large sunspot on the low sun, wrapped in haze, enabling a naked eye observation? I remember to have seen two large sunspots through haze myself in the early hours of 2003 October 28 (which gave rise to spectacular aurora a few days later).
Of course, it would be nice if this conclusion is supported by other observations of the same sunspot on 1835 June 16. Drawings of sunspots aren’t commonplace in the early nineteenth century. That’s what makes this card so special. The Royal Astronomical Society in London keeps observations of sunspots by Thomas John Hussey. Just a day after our anonymous card player noted his single point on the sun, on 1835 June 17, Hussey recorded a total of three sunspots: a prominent spot on the very southern edge of the solar disc, a quite small spot close to the sun’s northern rim and a large one located at a position similar to the sketch on the back the playing card. See the image to the left.
Also, the RAS keeps observations of Samuel Heinrich Schwabe. This German amateur astronomer started observing sunspots in 1825, expecting to discover a new planet closer to the sun than Mercury. On 1835 June 14 he also recorded three sunspots, which are in similar arrangement as Hussey’s recording. See the image to the right. The sunspot which corresponds with the spot sketched on the playing card is quite large with a broad penumbra and should be visible to the unaided eye under the right conditions.
So, I believe that the back of the playing card indeed shows us the recording of a large sunspot, seen with the naked eye through the haze in the early hours of a summer morning in 1835. Many thanks to Mary Chibnall of the Library of the Royal Astronomical Society for providing me copies of Hussey’s and Schwabe’s sunspot drawings!