Shell star Shell star A shell star is a star having a spectrum that shows extremely broad absorption lines, plus some very narrow absorption lines. They typically also show some emission lines, usually from the Balmer series but occasionally of other lines. The broad absorption lines are due to rapid rotation of the photosphere, the emission lines from an equatorial disk, and the narrow absorption lines are produced when the disc is seen nearly edge-on. Shell stars have spectral types O7.5 to F5, with rotation velocities of 200–300 km/s, not far from the point when the rotational acceleration would disrupt the star.
A Star Is Burns play in the opening moments of the episode is a parody of "U Can't Touch This" by MC Hammer. The opening of Bart's film "The Eternal Struggle" is a reference to The Amazing Criswell's narration in "Plan 9 from Outer Space". Barney's film contains references to "Koyaanisqatsi", and the music of the film, which was composed by Philip Glass. Barney's film also features musical selections from the aria "Un bel di vedremo" from Act II, pt. 1 of Puccini's opera "Madama Butterfly". In its original broadcast, "A Star Is Burns" finished 57th in the ratings for the week of February