To Map the Stars: How Star Charts Work
To Map the Stars and Planets Above
Every star chart begins with the impossible task of fitting an infinitely large 3D sphere to paper. Our night sky has no edges, no corners, no single place to be cut open, so there is no solution that does not distort one part or another. However, for thousands of years, people have found ways around this issue. This hub explores these ways. Our resources examine the geometry that flattens the dome with the least possible distortion, explains stellar coordinate systems, and explores how early cultures used the night sky as a calendar.
Astrolabe
The Astrolabe, the thousand-year-old tool that helped ancient cultures navigate by the stars.
What Star Charts Show
What a Star Chart Actually Shows You. Every star chart makes four promises about the sky. Here’s how to read all of them.
Stereographic Projection
The Mathematics of Stereographic Projection. Geometry that lets a round sky lie flat on paper, and why it keeps every circle a circle.
Star Coordinates
Three Ways to Locate a Star. Altitude, right ascension, ecliptic longitude: three coordinate systems, to name a star.
The Stars a Calendar
How the Sky Became a Calendar. Before it was a science, astronomy was a calendar. How watching the sky taught us to count the years.
The Map That Keeps Its Circles
A sphere can’t be flattened onto a plane without breaking something. A light shines down from the top of the sphere, casting every point as a shadow on the plane below. There’s distortion at the edges, but circles stay circles and angles stay true. Explore the model in 3D and see for yourself why it’s so useful for mapping the stars.