COSMOS IoW_20181221 - Gaia

IoW_20181221 - Gaia

Image of the Week

A sonification of Gaia Data

Figure 1: Score of the song: bright stars represent a high pitch, faint stars represent a low pitch Image credit: Thomas Boch (CDS)

A first sonification of Gaia data has been developed during ADASS 2018 at the hackathon. A team of engineers from the Centre de Données astronomiques de Strasbourg (CDS) and a student from the University of Maryland created "the music of light curves", an attempt to generate melodies from the light curves of Gaia Data Release 2 variable stars. The hack results can be found here on github with a PDF containing the detailed explanation. To launch the demo, click here.

Inspired by this first experiment, we decided to make Gaia stars sing to celebrate the festive season.

This application is no longer supported. Please be referred to the video further below.

Gaia song: click on the play button to start the song. Created using Aladin Lite. You can move around the sphere to see all areas of the sky. Credit: Thomas Boch (CDS) using data from ESA/Gaia/DPAC. (There is a known issue with the sound in newer versions of the Safari browser, you can scroll down for the video version)

Data used

Use is made of a Gaia DR2 sample, which contains the 1000 brightest stars that have a good parallax quality. It has been retrieved from the ESA Gaia Archive running the below ADQL query. The result from the query has been retrieved as a VOTable document and is available from github as well. When checking out the sky map above, you will see that clicking on individual sources will display a popup with the Gaia data for the associated source.

select top 1000
ra, dec, source_id, parallax, parallax_error, pmra, pmdec, phot_g_mean_mag, phot_bp_mean_mag, phot_rp_mean_mag, radial_velocity
from gaiadr2.gaia_source
where parallax_over_error > 10
order by phot_g_mean_mag ASC

Assigning music notes to stars

Contrary to the music of the light curves hack, the music notes were set in advance, imposed by the song score. Thus, the aim is to find which stars play a specific note. The "Jingle Bells" score is made of 10 distinct notes: D4, E4, F#4, G4, A4, B4, C5, D5, E5, and G5. We sorted our data sample by descending magnitude (i.e. ascending brightness) and assigned the 100 first (faintest) stars to the lowest pitch note (D4), the following 100 to the second lowest pitch note (E4), and so on until the last group of 100 brightest stars are assigned the highest pitch note (G5).

Creating music in the browser

The Tone JS library has been used to generate sounds in the browser.

Background data

The background imagery is the Gaia DR2 flux map made from the 1.7 billion measurements of the table.

Sky map viewer

The sky map viewer is provided by Aladin Lite, an embeddable sky atlas developed at CDS able to display survey images and to superimpose catalogue data. Aladin Lite documentation explains how to embed it on a web page.

It also comes with a full-featured API allowing one to customize its interface, control the view, change the image survey to display, create catalogues and overlay layers, develop powerful interactions between a web page and Aladin Lite.

As an example, here is a page built on Aladin Lite enabling the exploration of Gaia Data Release 2 data.

How to make it snow!

The Snowstorm project has been used to add some snow effect and tweaked to let the snow accumulate at the bottom of the crystal ball as the song progresses.

Make your own song with Gaia stars!

The source code of the animation is available in this github repository by Thomas Boch. If you want to make the stars play another song, here are the detailed step-by-step instructions:

Clone the repo
Find a MIDI version of the song you would like to play. Midiworld.com is for example a place to search for such versions.
Convert the MIDI file to a ToneJS track, using for example the MidiConvert online tool.
Edit the file `data/midi-track.js` and assign the result of the previous step to a variable of your choosing, for instance:

"var myTrack = { "header": { "PPQ": 240, "timeSignature": [ 4, 4 ], "bpm": 120, "name": "" }, ... "
Open and edit file 'js/app.js' in order to update the definition of variable 'songParams' and assign myTrack as the value of 'data' attribute.
You must also assign the 'trackIdx' and the 'synth' used for 'mainVoice' and possibly for the 'otherVoices'. Available synths are described in 'StarsAnimation.synths': allowed values are 'pulse', 'square', 'triangle', 'drums' and 'poly'. As an example, here is how Jingle Bells track is described:

"var songParams = { data: jingleBells, mainVoice: {
trackIdx: 1, synth: 'pulse' }, otherVoices: [ { trackIdx: 4, synth: 'square' } ] };"
Reload the index.html in your browser
Enjoy!

LYRICS FOR THE SONG

To be extra festive and to wish you all "Happy Holidays", the Gaia team at ESA/ESTEC created some lyrics to go along with the song. So sing along with Gaia: