Attributions

1. The artwork for the cat sprites is in the public domain and was created by Shepardskin on OpenGameArt.
2. The figure for standard configuration of coordinate systems for Galilean transformations is in the public domain and was created by Gerd Kortemeyer on Wikimedia Commons.
3. The artwork for the observer sprites is in the public domain and was created by devurandom on OpenGameArt.
4. The black hole visualization on the cover is in the public domain and was created by Jeremy Schnittman at NASA's Goddard Space Flight Center.
5. The figure for radial and transverse velocity was created by Brews ohare and CheChe on Wikimedia Commons and is licensed under CC BY-SA 3.0.