STRAUSS: Tour of the Solar System Sonifications
Here we give two examples of how we used our new sonification code STRAUSS to turn data into sound for the show Audio Universe Tour of the Solar System. This information is summarised in Harrison et al., to appear in Communicating Astronomy to the Public Journal. The resulting sonification of the data described below can be heard on our page on this website 'Science Behind the Show'.
Sonification of Earth's Rotation
Fig. 1: Diagram demonstrating our data sonification of the Earth’s rotation. Panel a) shows water covering fraction (left axis) versus longitude (top axis) over two Earth rotations with a world map projection as a grey underlay. These values are used to calculate the low-pass filter cutoff frequency for the sonification (right axis). Panel b) shows the waveform of the sonification as a function of time. Panels c) and d) demonstrate the effect of the filter on the waveform by zooming into 20 milli-second windows around longitudes where the water covering fraction is approximately highest and lowest, respectively (indicated by vertical lines of corresponding colour in Panel a).
We wanted to sonify sunlight bouncing off the spinning Earth through changing timbre as the Sun passes over water (a “brighter” sound) or land (a “darker” sound). For this, we used data of the covering fraction of water as a function of longitude. The data are from the GEBCO 2021 bathymetry, which assigns water or land to each cell of a 15x15 arcsecond grid across the Earth (Fig. 1). To create the sonification, we started with a sustained musical chord, using notes G flat 3, D flat 4, E 4 and B 4. Each note was created from a set of three sawtooth oscillators combined at frequencies on, 2% above and 2% below the target pitch. These choices provide a harmonically rich sound, which is then manipulated by filtering out frequencies (i.e. subtractive synthesis) based on the water covering fraction data.
Sonification of Stars Appearing in the Night Sky
Fig. 2: Diagram demonstrating our sonification of the ‘stars appearing’. Panel a) shows the mapping of V-band magnitude (top axis) and B-V colour (left axis) to triggering time in the audio sequence (bottom axis) and musical note (right axis), respectively. The aligned Panel b) shows the waveform produced for a stereo setup, and the triggering times of the 10 brightest stars (dotted lines). The right panel shows the stellar sky chart, with point size and colour indicating brightness and B-V colour, respectively. In our sonification the observer faces south, with the left and right audio channels corresponding to the east and west cardinal directions, respectively.
The audience ‘listen’ to stars that appear around them at the European Southern Observatory’s Very Large Telescope (VLT). The data we used are presented Fig. 2, which are the magnitudes, colours and coordinates of stars as viewed from the VLT on the 13th September 2019. We only considered stars with V-band magnitudes <6, to roughly correspond to the detection limit of the human eye.