Interactive HEALPix maps with Bokeh
One of the most common plots in astrophysics is the 'all sky map', which visualises the value of some quantity across the entire sky. For instance, you can visualise the number of stars per square degree catalogued by the European Space Agency's Gaia space telescope by downloading a dataset from CDS and plotting it with the Python healpy library. These visualisations are attractive, but really not that useful. You can compare two points on the sky and tell which has a greater density of stars, but you can't answer detailed questions like 'what are the coordinates of this interesting cluster of stars?' or 'how many stars are at this precise location?' They are also quite large files, requiring a large number of image pixels to represent the shapes of the much smaller number of HEALPix pixels (which are misaligned with the x-y pixels on your screen). I decided to address these issues by creating an interactive version of these plots using the Python Bok...