Donnerstag aus Licht (Thursday from Light) is an opera by Karlheinz Stockhausen in a greeting, three acts, and a farewell, and was the first of seven to be composed for the opera cycle Licht: die sieben Tage der Woche (Light: The Seven Days of the Week). It was written between 1977 and 1980, with a libretto by the composer.

Donnerstag was given its staged premiere on 15 March 1981 by the La Scala Opera in the Teatro alla Scala in Milan, but without the third act, which had to be omitted due to a strike by the opera chorus of La Scala. They had demanded soloists' bonuses because of one brief passage in act 3, and had been turned down by the management. Further performances without the third act followed on 18, 21, 24, and 27 March. An agreement was finally reached and the complete opera was finally performed on 3 April, with two further performances on 5 and 7 April (Kurtz 1992, 213). The stage direction was by Luca Ronconi, with costume and stage design by Gae Aulenti. Scenic realisation was by Giorgio Cristini, lighting by Vannio Vanni, light compositions (act 3) by Mary Bauermeister. Péter Eötvös conducted, and played the Hammond organ in act 3, scene 2. Karlheinz Stockhausen was the sound projectionist.

On 19 December 1981, Donnerstag was awarded the Premio Critica Musicale F. Abbiati for "best new work of contemporary music" (Stockhausen 1989a, 189).

A second staging was given by the Royal Opera, Covent Garden in London, on 16, 18, 20, 24, and 26 September 1985. The stage direction was by Michael Bogdanov, designed by Mari Bjornson, lighting and light compositions by Chris Ellis. Péter Eötvös conducted, and Stockhausen was the sound projectionist.

The second act, Michaels Reise um die Erde (Michael's Journey Around the Earth) was staged separately in 2008, by Carlus Padrissa (es) of La Fura dels Baus, with stage direction by Roland Olbeter. It was performed by Marco Blaauw (trumpet), Nicola Jürgensen (basset horn), and musikFabrik, directed by Peter Rundel. Video was by Franc Aleu, dramaturgy by Thomas Ulrich, lighting by Frank Sobotta, and sound direction by Paul Jeukendrup. This was initially a production of the Wiener Taschenoper in collaboration with the Wiener Festwochen. In 2013, this production was revived for three performances at Avery Fisher Hall in New York as part of the Lincoln Center Festival, beginning appropriately on Thursday, 18 July (Tommasini 2013).

Donnerstag is an opera for 14 performers (3 voices, 8 instrumentalists, 3 dancers) plus a choir, an orchestra, and tapes. It was composed between 1977 and 1980. In the larger context of Licht, Thursday is Michael's day. Thursday's exoteric (primary) colour is bright blue, and its esoteric (secondary) colours are purple and violet (Stockhausen 1989a, 182; Stockhausen 1989b, 200). Thursday is also the day of plants (Stockhausen 1989b, 201).