Question: Christoph Willibald Gluck and Camille Saint-Saëns, have which occupation in common?
Context: Gluck is a crater on Mercury.  It has a diameter of 105 kilometers.  Its name was adopted by the International Astronomical Union in 1979.  Gluck is named for the Austrian composer Christoph Willibald Gluck, who lived from 1714 to 1787. Déjanire is an opera (tragédie lyrique) in 4 acts composed by Camille Saint-Saëns to a libretto in French by Louis Gallet and Camille Saint-Saëns.  The last of Saint-Saëns' operas, it premiered on 14 March 1911 at the Théâtre de Monte-Carlo.  One of the opera's central characters, Hercule (Hercules), had been the subject of two earlier symphonic poems by Saint-Saëns – "Le Rouet d'Omphale" (1872) and "La Jeunesse d'Hercule" (1877).  The story is based on "The Trachiniae" by Sophocles (also the source for Handel's opera "Hercules"). Paride ed Elena (] ; "Paris and Helen") is an opera by Christoph Willibald Gluck.  It is the third of Gluck's so-called reform operas for Vienna, following "Alceste" and "Orfeo ed Euridice", and the least often performed of the three.  Like its predecessors, the libretto was written by Ranieri de' Calzabigi.  The opera tells the story of the events between the Judgment of Paris and the flight of Paris and Helen to Troy.  It was premiered at the Burgtheater in Vienna on 3 November 1770. L'île de Merlin, ou Le monde renversé (Merlin's Island, or the World Upended) is an opéra comique in one act composed by Christoph Willibald Gluck to a 1753 French libretto by Louis Anseaume based on Alain René Lesage and D'Orneval's 1718 vaudeville comedy "Le monde renversé".  Gluck's version was first performed on 3 October 1758 at the Schönbrunn Palace in Vienna. Charles-Camille Saint-Saëns (] , traditionally pronounced ] in French; (9 October 183516 December 1921) was a French composer, organist, conductor and pianist of the Romantic era.  His best-known works include Introduction and Rondo Capriccioso (1863), the Second Piano Concerto (1868), the First Cello Concerto (1872), "Danse macabre" (1874), the opera "Samson and Delilah" (1877), the Third Violin Concerto (1880), the Third ("Organ") Symphony (1886) and "The Carnival of the Animals" (1886). The city of Paris has been an important center for European music since the Middle Ages.  It was noted for its choral music in the 12th century, for its role in the development of ballet during the Renaissance, in the 19th century it became famous for its music halls and cabarets, and in the 20th century for the first performances of the Ballets Russes, its jazz clubs, and its part in the development of serial music.  Paris has been home to many important composers, to name a few: Jean-Baptiste Lully, Jean-Philippe Rameau, Christoph Willibald Gluck, Niccolò Piccinni, Frédéric Chopin, Franz Liszt, Jacques Offenbach, Georges Bizet, Claude Debussy, Maurice Ravel, Hector Berlioz, Paul Dukas, Gabriel Fauré, César Franck, Charles Gounod, Jules Massenet, Vincent d'Indy, Camille Saint-Saëns, Erik Satie, Igor Stravinsky, Sidney Bechet... Henri-Joseph Rigel (9 February 1741 – 2 May 1799) was a German-born composer of the Classical era who spent most of his working life in France.  He was born in Wertheim am Main where his father was musical intendant to the local prince.  After an education in Germany, where his teachers included Niccolò Jommelli, Rigel moved to Paris in 1767.  He quickly acquired a reputation in musical circles and published harpsichord pieces, string quartets, symphonies and concertos.  He began composing for the Concert Spirituel, most notably four hiérodrames (oratorios on sacred themes): "La sortie d'Egypte" (1774), "La destruction de Jericho" (1778), "Jephté" (1783) and "Les Macchabées" (score lost).  These show the influence of Christoph Willibald Gluck, and Gluck himself praised "La sortie d'Égypte".  Between 1778 and 1799 Rigel also wrote 14 operas, including the "opéra comique" "Le savetier et le financier" (1778). Salieri's opera was first performed at the Vienna Burgtheater on 2 June 1771, and his composition was much influenced by the aesthetics of Christoph Willibald Gluck, who attempted to reform "opera seria" by tying the drama more closely to the music.  Salieri's overture follows the principles set out by Gluck in the preface to "Alceste".  Other Gluckian influences display themselves in the frequent interplay of soloist and chorus, and the heavy use of chorus overall. The following discography for Gluck's opera "Orfeo ed Euridice" is mainly based on the research of Giuseppe Rossi, which appeared in the programme notes to the performance of the work at the 70th Maggio Musicale Fiorentino in 2007, under the title "Discografia – Christoph Willibald Gluck – Orfeo ed Euridice (Orphée et Eurydice)".  Rossi's data has been checked against the sources referenced in the notes. Christoph Willibald (Ritter von) Gluck (] ; 2 July 1714 – 15 November 1787) was a composer of Italian and French opera in the early classical period.  Born in the Upper Palatinate (now part of Germany) and raised in Bohemia, he gained prominence at the Habsburg court at Vienna, where he brought about the practical reform of opera's dramaturgical practices that many intellectuals had been campaigning for over the years.  With a series of radical new works in the 1760s, among them "Orfeo ed Euridice" and "Alceste", he broke the stranglehold that Metastasian "opera seria" had enjoyed for much of the century.
Answer: composer