This music was made using Granular Synthesis, a technique developed at IRCAM, in Paris. It's a method of manipulating audio samples. You could think of it as a microscope that focuses on minute grains of audio, in this case, trumpets. So the sounds rendered are basically defined by how you move and focus the microscope around in the audio. There are other techniques used here as well, like Sampling, Formant Filtering (for choir sounds), Subtractive Waveform Synthesis and good old fashioned overdubbing. Happy star gazing
Images courtesy of Spacetelescope.org