Urmas Sisask (born September 9, 1960) is an Estonian composer. One of the major inspirations for his music is astronomy. Based on the trajectories of the planets in the solar system, he created the planetal scale, a mode consisting of the notes C#, D, F#, G#, and A. Later, he discovered to his surprise that this was exactly the same as the Japanese Kumayoshi mode. Apart from choral works Urmas Sisask has written chamber, instrumental and orchestral music.