Stars in the Milky Way – Celestial Globe

This 3D model provides a novel way of viewing the distribution of stars throughout our Milky Way Galaxy. It presents a 360° view of our sky, inverted to form an inside-out representation across the surface of a sphere.

We reside within the Milky Way galaxy. The stars and dust in our galaxy form a kind of flattened pancake shape, and we are located between its center and edge. From this interior position we see most of our galaxy as a bright band that sweeps across the entire sky. That becomes a ridge running along the equator of this globe.

Models that translate image brightness into 3D printable "terrain" provide us a novel way to experience astronomical images as both a tactile and visual experience. They encourage us to look at the data differently, and often enable us to notice features we would not have picked out in a traditional image.

What data went into this model?

This model uses infrared observations made by NASA’s SPHEREx space telescope. It is a highly accurate map of the glow of stars throughout our galaxy when the obscuring effects of dust have been removed.

SPHEREx images the entire sky in 102 separate colors of light at wavelengths ranging from 0.7 to 5 microns. This globe used a selection of channels around 4.8 microns.

At these longer wavelengths, dark patches of dust that obscure our visible light view of the Milky Way have become transparent, revealing the cumulative glow of stars all the way out to the outer edges of our galaxy.

You can learn more about the original image used for this print on the AstroPix site.

Data from SPHEREx and many other astrophysics projects are available to download from the NASA/IPAC Infrared Science Archive (IRSA).

What does this model show us?

Note that this globe is NOT a 3D model of our galaxy.

Instead it gives us an alternative way to see the brightness of the sky, represented by the elevation of the globe’s surface. Brighter features create higher “terrain.”

The ridge running along the equator of this globe represents the glow of starlight throughout our galaxy. The largest peak is the very center of our galaxy, and the sharp ridges extending to either side side are the glow of stars from the the farthest reaches beyond that. Two of the Milky Way's closest neighbors, the Large and Small Magellanic Clouds, stand out as mounds just below and to the right of the center of our galaxy.

While the data used in this model is only two-dimensional, it does provide clues about the three-dimensional structure of our galaxy. Due to the effects of perspective, the most distant portions of the galaxy’s disk are projected into a very thin stripe which forms the sharpest ridge on the model.

The cumulative glow from stars that are closer to us begin to expand outwards from this equatorial band, with the very closest material approaching the poles due to the same perspective effects. This is like how nearby trees can block our view of the sky, but a distant grove will appear as a thin strip along the horizon.

Data Processing

This model is not an exact representation of the original image data; several steps were take to make it work more effectively as a 3D print.

The source all-sky data were processed and projected into an equirectangular map. A greyscale image was produced by running the data through an inverse hyperbolic sine (asinh) that keeps the fainter features in linear proportions while reducing the brightest features logarithmically. This was needed to keep bright features from turning into sharp spikes.

The image was then filtered to remove isolated points of light (bright stars and galaxies). This keeps the printed globe from turning into a pin cushion, but it also keeps the focus on the bulk distribution of stars rather than a handful of outliers.

The final mesh was created in Blender using a procedural workflow that displaced the surface of a fine mesh using the imported greyscale image, treating brightness as elevation. This mesh was further smoothed procedurally to reduce sharp features.