The Stellar Choir
The Stellar Choir is an interactive choir of roughly 8,500 "singing" stars that I built from an early data release of star light curves by NASA's Kepler Mission. The Stellar Choir has been recently included in the Official NASA website for this Mission, in both the sections of Education and Audio Gallery.
The original light curves were discarded as targets for the search of extra solar planets because of their high degree of variability. To build the sounds, a day of light measures was compresed into a second of sinusouidal sound; and changes in light flux were translated into changes in the pitch of the sound.
The Kepler spacecraft (launched in March 2009) is the space-based observatory of NASA's Kepler Mission -named after Johannes Kepler, the
17th-century astronomer. The goal of this mission is the discovering of Earth-like planets orbiting other stars. The spacecraft's photometers point to a star-enriched region in the constellations
of Cygnus, Lyra and Draco. The detection of extra solar planets is a challenging task because the blinding
brightness of stars prevents a direct observation of any orbiting planet, even more when the planet is as small as Earth.
Instead, the method used by the Kepler spacecraft involves the detection of the very slight reduction of the apparent star brightness that occurs when a planet transits between the star and Earth. This transit method can not be applied to stars whose magnitude changes intrinsically over time (variable stars). In fact, in the first month of the mission about 7,500 stars where cataloged as variable and dropped from the list of potential targets (a list comprising around 150,000 stars). On November 4, 2009, the light curves for the dropped stars where publicly released. A typical example of such curves is plotted in the next figure.
The irregular shape of this curve, together with its notable degree of smoothness, reminds that of the melograms that we studied in collaboration with Musicologist Teresa Ruiz-Coll in a work
about vocal microtonality. This happened with so many examples within the released set that its potential implications for musical composition could not be avoided. What about translating these curves into sound? Since these curves display the change in brightness along a
time period of almost 10 days, the translation could be made in a very direct way: time was compressed (one day of measure was converted into one second of sound), and the pitch of the evolving
sound was made proportional to the brightness values. So, light curves were converted into melograms, which could be ultimately converted into sound, as we did in our musicological studies.
A toy version of The Stellar Choir is displayed below. The full and big size version of The Stellar Choir can be found here.
The map displays the region of the sky surveyed by the Kepler spacecraft (a gnomonic projection centered on RA: 19h 20m, Dec: +45°). The blue squares plot the limits of the field of vision of Kepler's 42-CCD array. I placed a red marker on the astronomical coordinates of each of the variable stars whose light curve was converted into sound. This version only includes the sound for the first 1001 stars in the released set (those located in the bottom corner of Kepler's field).
Follow the instructions below to listen how the corresponding star "sounds"; or "sounded"!, since, depending on the given star, the light was emitted from 600 to 3000 years ago. This "Stellar Choir" is as old as big!
There are precedents of using astronomical data for musical purposes, but in many cases the data should be exhaustively manipulated to produce an interesting musical result. In the case of the Kepler measurements, the musical content of the data was almost direct: you only have to convert brightness into pitch, and compress the time.
- You'll have to zoom a lot to distinguish the red markers individually!
- Press a marker to play the corresponding sound.
- The sound will start automatically. After a sound is finished, it can be played again by pressing the corresponding button in the player below the sky map.
- Up to 4 sounds can be played simultaneously (4-part polyphony).
- The same sound can be loaded multiple times (round, or unison imitative counterpoint).
- Press the Reset button to go back to the initial state.
Conduct The Stellar Choir by yourself!