Stars & Constellations

Looking up at the night sky is a humbling experience. You can’t help but wonder about the big questions. The view might be frightening sometimes, but it’s always beautiful. This chart of stars and constellations is my attempt in capturing this feeling while mapping out the heavens.

You can get a high quality print of the map here:

Get it on redbubble

Reading a Star Chart

This map shows the Northern Hemisphere. As an analogy, it’s useful to imagine that there’s a giant sphere around the Earth with all the stars painted on it. If you cut this sphere in half along the equator, take the top part, and flatten it out, you end up with this map. This means the very center of the map shows the sky above the North Pole. Conveniently, there’s a bright star almost exactly at that point — Polaris. Of course, depending on your location on Earth, Polaris will most likely not be directly overhead (but it can serve as a handy point of reference).

To locate certain stars, you can use constellations. For instance, Ursa Major is quite easy to spot. You can then use the lines of the constellation to give you a rough direction for finding other stars and constellations (for example, you can find Arcturus by following the handle of Ursa Major to the left).

To precisely describe the position of a star or celestial object (e.g., galaxies), celestial coordinates are used. These work very similarly to latitude and longitude on Earth and are called declination (Dec) and right ascension (RA). Right ascension uses the unit “hour” — like a clock — to indicate the object’s direction. Declination tells you the distance from the center of the map and is measured in degrees. The North Star is located at about 90° Dec, and the horizon of the Northern Hemisphere (the celestial equator) is at 0° Dec. There’s a grid on the map to help with finding specific locations.

The dashed circle intersecting the grid is the ecliptic. The ecliptic is the path the Sun and other planets follow across the sky. You can see that the ecliptic passes through all the constellations that are zodiac signs. In fact, zodiac signs are determined by the Sun’s position along the ecliptic at the time of birth. The ecliptic is offset from the grid because Earth’s axis is tilted relative to the axis of the solar system. There’s a schematic drawing at the bottom of the map to help visualize this:

In the drawing, you also see the vernal equinox. This is the point where the ecliptic intersects the celestial equator. This is used as a reference point for right ascension: The right ascension at the vernal equinox is 0h. There’s also a second intersection on the opposite side, the autumnal equinox. These points are also used for defining the astronomical seasons: The sun crossing the vernal equinox marks the beginning of the astronomical spring.

The Visuals

My requirements for this project were as follows:

The chart should be easy to read, contain as much information as possible, and look beautiful.

Regarding the layout, I experimented quite a bit, but I ended up with this airy open layout which aims to reflect the feeling you get when looking at the night sky.

For the same reason, I decided to not confine the stars to the grid in the center (just their labels), but to plot them all over the layout. I use a vignette to direct the focus to the center of the chart, which is also the center point of the Northern Hemisphere.

Additional graphic elements like the legend were created in Affinity Publisher. For the drawing at the bottom, I created a 3D-model in Blender and traced it.

Data is beautiful

This is my first big data-visualization project and something I wanted to do for years.

The stars, constellations and celestial objects were plotted with python. I used mathplolib for plotting and cartopy to map the data to a stereographic map projection. The icons for the stars and for the messier objects were created as vectors beforehand. I then imported the SVG-paths and used them as custom markers for my plot (using this tutorial).

The data comes from the openly available HYG Database as well as Stellarium.

Map projections are a rabbit hole – there are numerous possibilities to project a 3D sphere to a flat surface, each with its own advantages and tradeoffs. I chose a stereographic projection as it preserves directions and proportions. The tradeoff here is that the scale gets bigger towards the edges. Stereographic projection has been used in star maps for centuries, as it is well suited for locating stars and constellations in the night sky.

After plotting, there was still a lot of manual work to do. I composited the individual plots (grid, stars, star names, Bayer designations, constellation, constellation names, messier objects) with Affinity Publisher. There I also added the background gradient and repositioned a lot of labels for better readability.

This project owes a lot to Eleanor Lutz’s star map. Eleanor provided the code for her visualization together with a great documentation. Being new to cartography and python scripting, I doubt that I would have been able to complete this project otherwise.

I learned quite a lot about astronomy during this project. It took a while to wrap around my head around different map projections and celestial coordinates in the beginning.