The Prix Jules Janssen is the highest award of the Société astronomique de France, the French astronomical society. The Janssen Medal is an award presented by the French Academy of Sciences to those who have made advances in the area of astrophysics.
The Janssen-prize is an annual prize that is given to a professional French or foreigner astronomer in recognition of astronomical work in general. It was awarded for the first time in 1897 to French astronomer Camille Frammarion. The laureates of both prizes can be found on the respective Wikipedia page.
The Janssen medal was founded in 1886, though the first medal was only awarded in 1887. The award had been intended to be biennial, but in the beginning it was issued in every year. After the passing of the first seven years, in 1894 they returned to biennial or three-years awarding. Bernard Lyot French astronomer got the award pictured here in 1930.
Both awards are named for the French astronomer Pierre Janssen. (Born as Pierre Jules César Janssen, but mostly known as ules Janssen). On the obverse the same right facing portrait of him is visible as on the medal that was issued connecting to his greatest discovery in 1868. All these three medals are the work of the famous medalist Alphée Dubois, whose name can be read on the left side. On the right the inscription is: "J. JANSSEN DE L'INSTITUT".
On the reverse the name of the award is visible: "PRIX J. JANSSEN", that is Janssen-prize. This may be perplexing for the first sight as the medal in our case is a Janssen medal, not the Janssen-prize. The text engraved at the bottom reflects this: "ACADÉMIE DES SCIENCES", that is Academy of Sciences. Obviously both prizes award the same medal, but the academy engraves its name to the bottom for distinction. In the center the name of the awarded person (BERNARD LYOT) and the year of the awarding (1930) is visible in laureate. The gilt silver medal - which has a diameter of 68.5 mm and weight 167 gram - was struck by Paris Mint. Marks hit into the rim reflects this.
Lyot was also awarded by the Janssen-prize two years later in 1932.