MILKY WAY BLUES

Explanation: This musical expression lets you "hear" how our Milky Way Galaxy rotates. Radio telescopes observe different spectral emission lines to probe different phases of gas (atomic, molecular, ionized) in our Galaxy. Astronomers measure the Doppler shifts of these lines to determine gas velocities along the path that the telescope is pointing. To turn one of these observations into musical notes, the measured gas velocities are mapped to a pentatonic minor blues scale.

Every note you hear and circle you see represents gas that is either coming toward us (high notes and blue color) or going away from us (low notes and red color). Different gas phases are played by different instruments and shown by different colored borders on the circles. Each observation is represented by a line showing where the telescope was pointing and the positions of the circles along a line show the locations of the gas in the Galaxy. The star symbol shows the location of the Sun. The intensity of the emission coming from the gas is heard as longer note durations and shown as larger circles. With every new measure, the lines swing around to new observations.

Putting it all together, the variation of musical pitches heard in the Milky Way Blues portrays the motion of gas as it orbits around the center of our Galaxy.

— Sonification by: Mark Heyer — Visualization by: Greg Salvesen — Image by: Robert Hurt — Data Credit: Anderson et al. (2011); Kalberla et al. (2005);